15 -Miscellaneous Tumors ,CYSTS , and METASTASES .

Miscellaneous Tumors, Cysts, and Metastases Tumors of Cranial and Spinal Nerves Schwannoma (Neurilemoma, Neurinoma) Neurofibroma Malignant Peripheral Nerve Sheath Tumors (MPNST) Nonneoplastic Tumorlike Lesions Epidermoid Tumor Dermoid Tumor Lipoma Nonneoplastic Cysts Arachnoid Cyst Colloid Cyst Rathke Cleft Cyst Neuroglial (Neuroepithelial) Cyst Enterogenous Cyst Regional Tumors That Involve the CNS by local Extension Pituitary Adenoma Craniopharyngioma Metastatic Tumors Skull and Dural Metastases Leptomeningeal Metastases Parenchymal Metastases Limbic Encephalitis TUMORS OF CRANIAL AND SPINAL NERVES Schwannoma Etiology and pathology Etiology Schwannomas are benign tumors that originate from schwann cells The schwann cell is a neural crest derivative, and therefore schwannomas are classified as nonglial neuroectodermal tumors.1 Gross pathology Schwarmomas are4nd or lobulated well-delineated encapsulated tumors that arise eccentrically from their parent nerve.2 cystic or fatty degeneration and hemorrhagic necrosis are common (Fig 15-1) (Table 15-1) Microscopic appearance Two histologic types have been identified: Antoni type A and Antoni type B Antoni type A has compact interlacing bundles of fusiform neoplastic Schwann cells, reticulin, and Collagen.2 Well-developed cylindrical structures with palisading nuclei around a central core of cytoplasm, the classic “Verocay bodies,” are seen Antoni type B consists of a loosely textured stroma with widely separated stellate cells and no distinctive pattern.1 Incidence Schwannomas account for approximately 6% to 8% of all primary intracranial tumors.3 Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 627 Table 15-1 Comparison between schwannoma and neurofibroma Neurofibroma Schwannoma (plexiform type) Pathology Schwann cells Encapsulated Focal Round Cysts, necrosis, hemorrhage common Don't undergo ma- Malignant degenerlignant degenera- ation in 5% to tion 13% NF-2 NF-1 Fig 15-1 Gross pathology of a schwannoma with central necrosis and hemorrhage (Courtesy Rubinstein Collection, ed Forces Institute of Pathology.) Acoustic schwannoma is the most common cerebellopontine angle mass, accounting for 75% to 80% of lesions in this location (see Chapter 12) Schwannomas usually occur as isolated lesions Multiple schwannomas are seen in approximately 5% Of cases and are characteristic of neurofibromatosis type (NF-2).4 Approximately 18% of solitary schwannomas occur in the presence of neurofibromasis.5 Age and gender Age Schwannomas are primarily adult tumors They are most prevalent in older age groups (5th to 6th decades) When they occur with NF-2, schwannomas appear earlier, usually by the third decade.6 Schwannomas are rare in children, accounting for approximately 0.1% of pediatric intracranial tumors.6 Schwannomas are especially rare in the absence of neurofibromatosis Gender There is a slight female predominance (1.5-2:1).7,8 Clinical presentation Symptoms depend on the specific cranial nerve affected Vestibulocochlear nerve CN VIII is the most common location for intracranial schwannoma Despite the fact that most acoustic schwannomas originate from the vestibular segment, the earliest symptoms are usually tinnitus and sensorineural hearing loss.9 Vestibular symptoms are late manifestations Other symptoms depend on tumor size and extent These include symptoms of other cranial nerve involvement, brainstem compression, and obstructive hydrocephalus.9 Trigeminal nerve Because the fifth cranial nerve has an extensive intracranial course and traverses several distinct anatomic regions, trigeminal schwannomas have various manifestations.10 Eighty to ninety percent of gasserian ganglion schwannomas cause trigeminal dysfunction Symptoms are pain, Schwann cells + fibroblasts Unencapsulated Infiltrating Fusiform Cysts, necrosis, hemorrhage rare Incidence Common (6% to 8% of primary brain tumors) Uncommon (except in NF-1) Age 40s to 60s Any age Location Cranial nerves (es- Cutaneous and spipecially CN VIII) nal nerves (especially CN V1 peripheral branches, exiting spinal nerves) Imaging Sharply delineated Poorly delineated, infiltrating Heterogeneous Homogeneous (large lesions) T1WI: 67% hypoin- T1WI: mostly isointense, 33% isoin- tense with mustense cle T2WI: hyperintense T2WI: hyperintense Enhance strongly Enhance moderately/ intensely paresthesias, and masticatory muscle weakness, in decreasing order of frequency.11 Occult denervation atrophy can sometimes be identified on imaging studies in these patients (see subsequent discussion) Ophthalmic division (V1) involvement results in exophthalmos and diplopia Posterior fossa trigeminal schwannomas cause ataxia and facial and auditory nerve dysfunction.12 Atypical trigeminal neuralgia, lower cranial nerve palsies, pyramidal signs, and signs of increased intracranial pressure are found in 40% of patients Facial nerve Regardless of location, facial nerve paresis is the most common presenting symptom Schwannoma is nevertheless a rare cause of facial palsy, accounting for only 5% to 6% of cases; 80% are idiopathic (Bell palsy), with herpes zoster, otitis media, and trauma more common than schwannoma.13,14 628 PART THREE Brain Tumors and Tumorlike Processes Location General Excepting the first (olfactory) and second (optic) nerves, all cranial nerves have sheaths that are partially composed of Schwann cells and are therefore potential sites for intracranial schwannomas.5 Cranial nerve sheaths have two anatomically distinct components In one part the sheath surrounding the axons is formed by Schwann cells; in the other the sheath consists of oligodendroglial cells.9 Most schwannomas arise at the point where the axonal sheath switches from glial (oligodendrocyte) to Schwann cell origin.3 Schwannomas arise eccentrically from the outer nerve sheath layer and enlarge away from it, compressing rather than invading the nerve.13 Schwannomas have a distinct propensity to affect sensory nerves more than pure motor nerves CN VIII is the most commonly affected, with the trigeminal nerve root or ganglion next in frequency of occurrence Schwannomas arising from other cranial nerves are very rare.5 Vestibulocochlear nerve Ninety to ninety-five percent of intracranial schwannomas, arise from CN VIII Most all "acoustic schwannomas" originate from the inferior or superior vestibular division; cochlear schwannomas are rare.12 Trigeminal nerve Trigeminal schwannomas represent 0.07% to 0.28% of primary intracranial tumors and account for approximately 5% to 6% of all intracranial schwannomas.7,10 The most common location is the middle cranial fossa, site of nearly half of all trigeminal schwannomas CN V schwannomas that are totally or predominately within the posterior fossa account for another 15% to 20% "Dumbbell" shaped or "hourglass" tumors with significant components in both cranial fossae represent about one quarter of all trigeminal schwannomas Five percent of all schwannomas arise from distal intracranial CN V branches and extend extracranially (see Fig 12-165) These rare tumors commonly originate from the ophthalmic division.7,10,11 Completely extracranial head and neck schwannomas are uncommon They usually arise from the sympathetic chain, cervical plexus, or vagus nerve.1 Facial nerve The facial nerve is the third most common site of intracranial schwannomas Most facial schwannomas are intratemporal; all segments of the intrapetrous facial nerve can be affected, although the geniculate ganglion is the most frequent site.13,14 Involvement of multiple contiguous segments is also common.13 Schwannomas involving the intracranial or intraparotid facial nerve segments are rare Other cranial nerves Pure motor cranial nerves such as the oculomotor, trochlear, and abducens nerves are rarely involved by solitary schwannomas.15 This is particularly true in the absence of NF-2.4,5,16 Schwannomas of mixed XI) are also uncommon.17 These tumors occur as a purely cisternal mass, jugular foramen lesion, or a "dumbbell" lesion with both intra- and extracranial components Multiple schwannomas Multiple cranial nerve schwannomas are common with NF-23 ; bilateral acoustic nerve tumors are pathognomonic for NF-2 (see Chapter 5) Intracerebral schwannoma Schwannomas within the brain parenchyma is an exceedingly rare tumor; only 37 cases have been reported These tumors may arise from perivascular nerve plexi in the tela choroidea.18,18a Natural history Schwannomas are very growing benign neoplasms Despite their potential for regrowth following incomplete excision, schwarnnomas rarely, if ever, undergo malignant degeneration.2,19 Neurofibromas are much more likely than schwannomas to become malignant (see subsequer discussion) Imaging Plain film radiographs Bone changes on film radiographs are comparatively late manifestations of intracranial schwannomas Imaging vary with tumor location Widening of the auditory canal can be seen with moderate-sized acoustic schwannomas; smooth, sharply mar anteromedial petrous apex erosion is the most common plain film manifestation of trigeminal schwannoma.7 The middle cranial fossa floor may also be affected with enlarged foramen ovale, foramen rotundum, or superior orbital fissure.10 Hyperostosis and bone sclerosis are rare Angiography Reported angiographic findings in schwannoma vary, and a typical pattern is not clearly established.20 Many schwannomas are avascular or hypovascular lesions that are identified by focal displacement, stretching, and draping of adjacent vessels One quarter of reported cases show hypervascularity, contrast pooling, and prominent capsular veins.20 Diffuse vascular blush and arteriovenous shunting with early draining veins are uncommon Benign and malignant nerve sheath tumors cannot be distinguished by their angiographic patterns alone.21 CT Schwannomas are iso- or slightly hypodense to adjacent brain on NECT scans Calcification and hemorrhage are uncommon Virtually all schwannomas enhance strongly following contrast administration Small tumors usually show uniform enhancement, whereas larger lesions may have a heterogeneous pattern This is due to cystic degeneration, xanthomatous change, or areas of relative hypocellulari,7 adjacent to densely cellular or Chapter 15 Miscellaneous Tumors, Cysts, and Metastases pools of trapped CSF are sometimes associated with schwannomas.9 Trigeminal schwannomas with longstanding denervation cause atrophy and fatty infiltration of the masticatory muscles MR Large acoustic schwannomas demonstrate the characteristic findings of an extraaxial mass (Fig 15-2, A) There is a distinct CSF/vascular "cleft" between tumor and brain, the corticomedullary junction of the cerebellum is displaced, and the brainstem appears rotated (see Figs 12-61, B, and 15-2, B and 629 C) Most acoustic schwannomas form an acute angle with the petrous temporal bone The cisternal portion is typically larger than the intracanalicular segment, giving this particular tumor the appearance of ice cream on a cone (see Fig 12-63) Approximately two thirds of acoustic schwannomas are slightly hypointense to brain on T1WI (Fig 15-3); one third are isointense Most schwannomas have mild to markedly increased signal intensity on proton density- and T2-weighted sequences Foci of Fig 15-2 Axial gross pathology (A) of a vestibulocochlear schwannoma with fatty degeneration and small hemorrhagic foci (small arrows) Note the distinct cleft (large arrows) between the extraaxial mass and the brain (compare with Figs 12-61, B and 15-2, B and C) Axial postcontrast T1-weighted (B) and T2-weighted (C) MR scans in another patient show a typical large acoustic schwannoma The tumor (large arrows) enhances strongly but heterogeneously It is slightly hyperintense to brain on T2WI and has numerous intratumoral cysts (open arrows) Intracanalicular part of the tumor (curved arrow) Also note the compressed fourth ventricle (arrowheads) and rotated brainstem (A, Courtesy B Horten.) Fig 15-3 Sagittal T1- (A) and axial T2-weighted (B) MR scans of a large trigeminal schwannoma (large black arrows) show intratumor cysts (small arrows) and hemorrhage (open arrows) (Courtesy Timothy J Miller.) 630 PART THREE Brain Tumors and Tumorlike Processes cystic degeneration are common in larger lesions (Figs 1572, C and 15-3, Q, but frank hemorrhage is rare (Fig 15-3, A).22a Nearly all schwannomas show intense enhancement following contrast administration (see Fig 12-75) Enhancement patterns are homogeneous in 67% (see Fig 12-63, B), mildly inhomogeneous in 10%, and heterogeneous with areas of intratumoral cystic degeneration in 22% (Fig 15-2, B) Peritumoral edema is seen in 37%, and associated arachnoid cysts are present in 7% of cases (see Fig 12-63, B).23 The major differential diagnosis of - acoustic schwannoma is cerebellopontine angle meningioma The latter is typically a broad-based lesion that forms an obtuse angle with the adjacent dura (see Fig 1264) A dural "tail" is highly suggestive of, but not diagnostic for, meningioma (see Chapter 14) Other lesions that can mimic acoustic schwannoma include metastasis, hemangioma (see Fig 12-74, Q, postoperative fibrosis (see Fig 12-76), and inflammatory disease (see Fig 12-79).9,24 Neurofibroma Head and neck neurofibromas are usually plexiform tumors Plexiform neurofibromas are a unique feature of neurofibromatosis type (von Recklinghausen disease) and are considered pathognomonic of that neurocutaneous syndrome (see Chapter 5) Neurofibromas are not native to the intracranial cavity but occur in posterior ganglia as central extensions of peripheral tumors.2 Pathology Gross pathology Plexiform neurofibromas are unencapsulated tumors that diffusely infiltrate the affected subcutaneous tissue or nerve (Fig 15-4) Fusiform enlargement of multiple nerve fascicles and branches is characteristic In contrast to schwannomas, neurofibromas rarely undergo fatty degeneration, cystic necrosis, or hemorrhage2 (see Table 15-1) Microscopic appearance Plexiform neurofibromas contain a mixture of Schwann cells, fibroblasts, reticulin, and collagen fibers, and a loose mucoid matrix interspersed between axons of the parent nerve.2 In schwannomas, Schwann cells are the only proliferating cell type, mucopolysaccharide matrix is scanty or absent, and nerve fascicles are displaced rather than assimilated within the tumor.19 Incidence Plexiform neurofibromas occur only with NF-1 Age and gender Plexiform neurofibromas can be found at any age Both genders are equally affected Location Neurofibromas can extend along cranial Fig 15-4 Gross pathology specimen of the eyelid and adjacent scalp in a patient with an extensive plexiform neurofibroma The unencapsulated tumor diffusely infiltrates the soft tissues (arrows) (Courtesy Rubinstein Collection, Armed Forces Institute of Pathology.) nerves from peripherally located tumors The ophthalmic division of the trigeminal nerve is most commonly affected; the facial nerve is a less frequent site Natural history Between 5% and 13'% of plexiform neurofibromas undergo malignant degeneration Imaging Plexiform neurofibromas are poorly delineated, diffusely infiltrating masses that can expand foramina and erode bone (Fig 15-5, A) These lesions are typically isodense with muscle on NECT scans and show variable enhancement following contrast administration (Fig 15-5, B) Most neurofibromas are isointense on Tl-weighted MR scans, hyperintense on T2WI, and enhance moderately to intensely (see Figs 12-164 and 12-183) Malignant Peripheral Nerve Sheath Tumors Malignant transformation of schwannomas is extremely rare Between 5% and 13% of neurofibromas in von Recklinghausen disease become malignant Malignant nerve sheath tumors can also arise de novo within an otherwise normal nerve These so-called malignant peripheral nerve sheath tumor (MPNSTs) typically affect the retroperitoneum, mediastinum, and viscera, as well as large nerves of the neck and proximal extremities Malignant tumors can arise from the eighth nerve, but the trigeminal nerve is the most commonly affected cranial nerve.19 Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 631 Fig 15-5 Bone (A) and soft tissue windows (B) from an axial CECT scan in a patient with neurofibromatosis type (NF-1) show an extensive plexiform neurofibroma (arrows) that erodes the skull base The tumor enhances moderately NONNEOPLASTIC TUMORLIKE LESIONS Epidermoid Tumor Etiology Both congenital and acquired epidermoid cysts occur Congenital epidermoid "tumor" is actually a nonneoplastic inclusion cyst Epidermoid cysts probably arise from inclusion of ectodermal epithelial elements at the time of neural tube closure or during formation of the secondary cerebral vesicles24,25 (Table 15-2, p 632) Acquired epidermoid cysts develop as a result of trauma Here, epidermis is implanted into deeper underlying tissues and forms a cyst that continues to desquarnate keratin.26 Intracranial implantation epidermoid cysts are uncommon; most epidermal inclusions cysts are found in the lumbosacral spine following nonstylet needle puncture (see Chapter 21) Pathology Gross pathology Intracranial epidermoid tumors are well-delineated cystic lesions that insinuate along CSF cisterns They have an irregular lobulated, or "cauliflower-like" outer surface that often has a shiny "mother of pearl" appearance (Fig 15-6) The cyst interior is filled with soft, waxy, or flaky keratohyalin Fig 15-6 Two gross pathology cases illustrate the typical appearance of epidermoid tumors A, This suprasellar epidermoid tumor (arrows) is seen from below Note the shiny mother of pearl" appearance The tumor insinuates throughout the suprasellar subarachnoid space, engulfing vessels and cranial nerves at the base of the brain B, Close-up view of an epidermoid tumor that was removed from the cerebellopontine angle in another patient Note the lobulated, "cauliflower-like" surface to the tumor CSF is present between the tumor interstices (A, Courtesy E Tessa Hedley-Whyte B, From Gao P-Y, Osborn AG et al: AJNR 13:863-872, 1992.) 632 PART THREE Brain Tumors and Tumorlike Processes Table 15-2 Comparison between epidermoid and dermoid tumors Epidermoid Pathology Ectodermal inclusion cyst Dermoid Ectodermal inclusion cyst (no mesoderm) Squamous epithelium Keratinaceous debris Liquid cholesterol Squamous epithelium Keratinaceous debris Solid crystalline cholesterol No dermal append- Dermal appendages ages (hair, sebaceous glands) Grow by epithelial Grow by epithelial desquamation desquamation + glandular secretion Rarely rupture Commonly rupture Incidence 0.2% to 1% of pri- Uncommon (0.04 mary brain tuto 0.6% of primors mary brain tu4-9x more commors) mon than der moid Age 20 to 60 years M=F Location Imaging CT MR 30 to 50 years Slight male predominance Off-midline Midline 40% to 50% in cer- Parasellar, frontoebellopontine basal most comangle cistern; mon intracranial 10% to 15% para- sites sellar, middle Vermis, fourth fossa space; 10% ventricle most diploic space common infraInsinuates along tentorial sites CSF spaces Subarachnoid spread from ruptured cyst NECT: low density NECT: very low (like CSF); calcifi- density (like fat); cation uncomcalcification common mon; ± dermal sinus tract CECT: periphery CECT: no enhanceoccasionally enment hances T1-, T2WI: often Hyperintense on like CSF T1-, hypointense on T2WI material that results from progressive desquamatio of the cyst wall.27 Epidermoid cysts encase vesse6 and engulf cranial nerves (Figs 15-6, A, and 15-7) In some cases they invaginate deeply into adjacent, brain Microscopic appearance The cyst wall is composed of simple stratified cuboidal squamous epithelium, and the center is filled with keratinaceous debris and solid crystalline cholesterol The keratin, produced in successive layers by desquamated epithelium from the cyst wall, has a laminated appearance In contrast to dermoid cysts, epidermoid tumors not contain hair follicles or sebaceous glands.27 Incidence Epidermoid tumors represent 0.2% to 1% of all primary intracranial tumors.3 Age and gender Epidermoid tumors typically occur between the ages of 20 and 60 The peak incidence is the fourth decade 25 There is no gender predilection Location Ninety percent of cranial epidermoid tumors are intradural Intradural epidermoid tumors occur primarily in the basal subarachnoid spaces; offmidline sites are the common locations Between 40% to 50% are found in the cerebellopontine angle cisterns, making epidermoid the third most common CPA mass (after acoustic schwannoma and meningioma) Supra- and parasellar (cavernous sinus or middle cranial fossa) regions account for 7% each (see Fig 12-128) Intraaxial epidermoid tumors are uncommon The fourth ventricle is the most common site.28 Rarely, these tumors occur in the cerebral hemispheres or brain stem.27 Ten percent of epidermoid cysts are extradural, mostly intradiploic Primary intradiploic epidermoid cysts occur in the frontal, parietal, or occipital bones; the sphenoid bone is an uncommon site.29 Cranial dermoids and epidermoid cysts are the most common scalp lesions in children26 (see Chapter 12) Natural history The epithelium of epidermoid tumors proliferates at a rate comparable to normal epidermis, suggesting that these are not true neoplasms but benign cysts.19 Although malignant degeneration does not take place, local recurrence following subtotal resection is common Imaging Plain film radiographs Diploic space epidermoid tumors can affect any part of the skull: the scalp, diploe (inner or outer table alone or both), and sometimes the epidural space as well.30 Diploic e0der Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 633 Fig 15-7 Anatomic drawing of a typical posterior fossa epidermoid tumor The lobulated tumor insinuates throughout the CSF cisterns, engulfing the basilar artery and its branches, as well as the trigeminal nerve The tumor deeply invaginates the adjacent pons (From Gao P-Y, Osborn AG et al: AJNR 13:863-872, 1992.) moid cysts typically have round or lobulated, welldelineated focal bone erosions with sclerotic margins Angiography Cerebral angiography is usually normal or discloses avascular mass effect CT NECT scans show most epidermoid tumors are well-defined lucent-appearing lobulated masses with attenuation similar to CSF (Fig 15-8) Calcification is present in 10% to 25% of cases.27,31 Occasionally, epidermoid tumors appear hyperdense on NECT, possibly due to hemorrhage, high protein content, saponification of cyst debris to calcium soaps, or deposition of iron-containing pigment.25,32,33 Most epidermoids not enhance following intravenous contrast administration, although enhancement at the tumor margin is sometimes observed.27 Intrathecal contrast delineates the irregular, multilobulated tumor surface (see Fig 12-65, D) MR Most intracranial epidermoid tumors are confined to, and insinuate along, the basilar CSF cisterns (Fig 15-9; see Fig 12-128) Epidermoid tumors typically have long T1 and T2 relaxation times, signal characteristics that are similar to CSF s 15-8, B and C, and 15-9; and see Fig 12-65, B and C) Some epidermoid tumors have a lobulated rim that gives slightly higher signal than the hypointense central portion of the cyst (Fig 15-10) A thin hyperintense rim that probably represents CSF trapped around the mass or within its frondlike interstices is sometimes seen on proton densityweighted sequences.34 Some epidermoid cysts appear iso- or even hyperintense to brain on T1WI These so-called "white epidermoids" have high lipid content on magnetic resonance spectroscopy, whereas epidermoids with long T1 values (black epidermoids) have reduced lipid content on spectroscopy.28,35 Rarely, epidermoids show mixed signal intensities on both CT and MR.36 Differential diagnosis Although completely cystic schwannomas can sometimes mimic epidermoid tumor,37 the major differential diagnostic consideration is arachnoid cyst (see Fig 12-135).31 Steady-state freeprecession (SSFP) MR imaging is useful in differentiating tumors such as epidermoid from simple or complex benign cysts (see subsequent discussion) Diffusion-weighted MR can also be useful in distinguishing between arachnoid cysts and epidermoid 634 PART THREE Brain Tumors and Tumorlike Processes Fig 15-8 Axial CECT scan (A) of a cerebellopontine angle epidermoid tumor shows the lesion (large arrows) is very low density and difficult to differentiate from CSF The right trigeminal nerve (open arrow) is displaced and engulfed by the tumor Axial T1- (B) and T2-weighted (C) MR scans in the same case show the tumor (large arrows) extends inferiorly along the cerebellopontine angle cistern, deeply invaginating into the adjacent medulla (open arrows) (From Gao P-Y, Osborn AG et al: AJNR 13:863-872, 1992.) Fig 15-9 Coronal T1-weighted MR scan in a patient with an epidermoid tumor shows the mass (large arrows) fills; the cerebellopontine angle cistern and displaces the pons and medulla toward the opposite side This case nicely demonstrates tumor insinuation into the adjacent ambient and quadrigeminal cisterns (curved arrows) This epidermoid tumor is nearly isointense with CSF Fig 15-10 Coronal T1-weighted MR scan in a 52-year-old woman with a right cerebellopontine angle epidermoid tumor shows the lobulated tumor rim (large arrows) isointense with gray matter, whereas the center (open arrows) is very low signal and is nearly isointense with CSF Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 635 Fig 15-11 Gross pathology of a dermoid cyst is demonstrated A, The frontal mass (large arrow) ruptured into the lateral ventricles, filling both ventricles with an oily, cheesy fluid (small arrows) Note ependymitis (open arrows) B, Basal view of the cisterna magna shows opaque, thickened meninges (arrows), caused by the intense chemical meningitis (From archives of the Armed Forces Institute of Pathology.) tumors The apparent diffusion coefficient (ADC) of arachnoid cysts is similar to stationary water, whereas the ADC of epidermoid tumors is similar to brain parenchyma.38 Cystic astrocytomas, hemangioblastomas, and other low density cisternal masses such as enteric cyst are rarely confused with epidermoid tumors addition, dermoid cysts contain dermal appendages (hair follicles and sebaceous and sweat glands) Liquid secretions and breakdown products of these dermal appendages result in an oily mixture that contains lipid metabolites.39 Calcifications are common, representing dystrophic changes or dental enamel, another ectodermal derivative.40 Dermoid Tumors Etiology A common misconception about the origin and content of dermoid cysts is that they arise from inclusion of both ectodermal and mesodermal elements This so-called myth of the mesoderm derives from the misconception that hair, sebaceous, and sweat glands are mesodermal in origin They are not.39 These elements lie within mesodermal connective tissue, but their origin is the embryonic ectoderm Therefore both epidermoid and dermoid cysts are ectodermal inclusion cysts.39 Incidence Intracranial dermoids are rare, accounting for 0.04% to 0.6% of primary intracranial tumors Intradural dermoid cysts are four to nine times less common than epidermoid cysts.42 Pathology Gross pathology Dermoid cysts are well-defined, lobulated cystic masses that contain a thick, viscous oily fluid with lipid metabolites and liquid cholesterol derived from decomposed epithelial cells.40 A dermal sinus be present with spinal and posterior fossa lesions.2 If the cyst has ruptured, its fatty contents can spread into the ventricles and subarachnoid spaces, inciting intense meningeal inflammatory response (Fig 15-11).41 Microscopic appearance The outer cyst wall is composed of a dense fibrous capsule; the interior is lined with squamous epithelium, hair, and dermal appendages (see subsequent discussion) Desquamated debris containing cholesterol and keratin is common to both epidermoid and dermoid cysts In Location Dermoid tumors typically occur in or near the midline The lumbosacral spinal canal is the most common site (see Chapter 21), followed by the parasellar, frontobasal, and posterior fossa regions.41-43 The midline vermis or the fourth ventricle are the most frequent infratentorial locations Following rupture, dermoid contents can disseminate widely throughout the subarachnoid space and ventricles Age and gender Spinal dermoid tumors typically present during the first two to three decades of life (see Chapter 21); intracranial lesions become symptomatic during the third decade There is a slight male predilection.27 Clinical presentation and natural history Seizures and headaches are the most common symptoms of uncomplicated supratentorial dermoids.42,44 Dermoids increase in size through both epithelial desquamation and glandular secretion.45 Cyst rupture can result in chemical meningitis, seizure, vasospasm with infarction, and death.40 656 PART THREE Brain Tumors and Tumorlike Processes Fig 15-34 This 54-year-old man complained of visual difficulties Pre- (A) and postcontrast (B) coronal T1-weighted MR scans show a mixed signal suprasellar mass (A, arrows) that shows both nodular and rim enhancement (B, arrows) following contrast administration Craniopharyngioma Fig 15-35 Coronal pre- (A) and postcontrast (B) MR scans demonstrate the strikingly heterogeneous signal observed with some craniopharyngiomas Both hyper- (large arrows) and hypointense areas (small arrows) are present on the precontrast study, A Following contrast administration a thin enhancing rim is seen (B, small arrows) The solid tumor nodule enhances intensely but very heterogeneously (B, large arrows.) (Courtesy J Zahniser.) Intracranial Metastases Common Skull Leptomeninges (arachnoid/subarachnoid) Parenchyma (gray-white junction most common) Less common Dura Pia/subpial Rare Carcinomatous encephalitis Limbic encephalitis (paraneoplastic disease) Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 657 Nodular or rim calcification is present in nearly all pediatric craniopharyngiomas (Fig 15-33, A) and is identified in 50% of adult cases Cyst contents are typically slightly higher in attenuation than CSF Postcontrast studies demonstrate nodular or rim enhancement in more than 90% of all cases (Fig 15-33, B) MR Of all sellar region masses, craniopharyngiomas have the most heterogeneous MR imaging spectrum.96 Signal is highly variable (Fig 15-33, C and D) The most common pattern is a cyst that is hypointense on T1- and hyperintense on T2-weighted sequences (see Fig 12-125).105 Studies analyzing the craniopharyngioma fluid content conclude that the increased signal intensity on T1WI seen in some tumors is caused by high protein concentration, blood degradation products in free solution, or both.107 Craniopharyngiomas enhance strongly but heterogeneously following contrast administration (Figs.15-34 and 15-35) (see box, p 655) The differential diagnosis of craniopharyngioma includes Rathke cleft cyst, necrotic pituitary adenoma, thrombosed aneurysm, and cystic hypothalamic opticochiasmatic glioma.107a METASTATIC TUMORS CNS metastatic disease from extracranial primary tumors has many manifestations (see box, left) Direct geographic extension from nasopharyngeal and skull base malignancy was delineated in Chapter 12 Here we discuss the numerous manifestations of hematogenous metastases to the skull and dura, leptomeninges, and brain parenchyma We close our discussion of CNS metastatic disease by discussing an uncommon but important entity: limbic encephalitis Skull and Dural Metastases Skull metastases Calvarial metastases are common (see box) Breast and lung are the most frequent primary sites.2 Lesions range from subtle intradiploic metastases to large masses with extensive areas of bone destruction CT scans with bone algorithm reconstructions and wide window settings best delineate the osseous components Contrast-enhanced MR studies are superior for detecting subtle intradiploic lesions, delineating lesion extent, and determming involvement of underlying dura or brain (Fig 15-36).108 Dural metastases Dural metastases are less common than skull lesions Calvarial metastases commonly also involve the adjacent dura (Fig 15-37).2 Occasionally, focal dural metastases occur without associated calvarial lesions In some cases a solitary focal dural metastasis can be indistinguishable on imaging studies from a typical benign meningioma (Fig 15-38; see Fig 14-31).109 Fig 15-36 This middle-aged woman with metastatic renal cell carcinoma has extensive diploic metastases Coronal (A) and axial (B) T1-weighted scans show the large tumor mass (large arrows) Note intratumoral hemorrhage (open arrows) and prominent foci of high-velocity signal loss (curved arrows) The dura (small arrows) is largely intact and the mass remains mostly extradural However, a small subdural tumor focus (arrowheads) is present near the vertex The underlying cortex appears compressed and edematous 658 PART THREE Brain Tumors and Tumorlike Processes Fig 15-37 This patient has lung carcinoma metastatic to the calvarium Sagittal T1-weighted MR scans without (A) and with (B) contrast show an extensive enhancing mass (large arrows) that extends through the calvarial vault and under the galea Some subacute thrombus is seen in the distal SSS (curved arrow) The ISS, ICVs, vein of Galen, and torcular herophili show intense enhancement (B, open arrows), indicating flow is present and possibly even increased as a result of collateral drainage Fig 15-38 A, Gross pathology specimen in a patient with metastatic breast carcinoma shows a focal dural mass (arrow) that resembles meningioma B, Axial CECT scan in a 67-year-old woman with headaches and decreasing mental status shows an enhancing anterior falcine mass (large arrows) with extensive bifrontal edema (small arrows) Because the patient had no known malignancy, the preoperative diagnosis was meningioma Metastatic lung cancer was found at surgery (A, Courtesy Rubinstein Collection, University of Virginia.) Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 659 Fig 15-39 Pathology and imaging manifestations of pachymeningeal (dural) carcinomatosis A, Coronal gross specimen in this patient with disseminated breast carcinoma shows extensively thickened dura (arrows) with sparing of the brain and subarachnoid space B and C, Axial postcontrast T1-weighted MR scans in another patient with breast carcinoma show diffusely thickened meninges (arrows) Biopsy disclosed pachymeningeal carcinomatosis (A, From Okazaki H: Fundamentals of Neuropathology, ed 2, lgaku-Shoin Medical Publishers, New York, 1989.) Isolated dural or pachymeningeal carcinomatosis is a rare form of intracranial metastatic disease The meningeal fibrous layer of the dura is diffusely infiltrated by neoplastic cells, forming a thickened, somewhat nodular-appearing membrane that covers the brain and spares the underlying subarachnoid space (Fig 15-39).110 the leptomeninges (Fig 15-40) Focal tumor nodules are less common.111,112 The subarachnoid space can be diffusely involved with metastatic tumor The basal cisterns are the most common site.2 Subtle leptomeningeal and subarachnoid metastatic disease is best delineated on contrast-enhanced MR scans (Fig 15-41).113 Leptomeningeal Metastases Leptomeningeal metastases are more common than pachymeningeal metastases Although solitary leptomeningeal disease is rare, between 6% to 18% of CNS metastases also involve the arachnoid and subarachnoid space, pia, or both.110 Pial metastases Pial metastases typically occur in combination with arachnoid and subarachnoid tumor Isolated subpial tumor spread is more common with extension of anaplastic astrocytoma and glioblastoma multiforme than with extracranial primary tumors A rare form of metastatic disease, carcinomatous encephalitis, occurs when there is diffuse tumor spread to the cortex and meninges without formation of macroscopic masses.114 Diffuse tumor infiltration Arachnoid/subarachnoid metastases Diffuse or widespread multifocal tumor infiltrates and thickens 660 PART THREE Brain Tumors and Tumorlike Processes Fig 15-40 Axial postcontrast T1-weighted MR scans show diffuse leptomeningeal and subarachnoid enhancing tumor (arrows) in this elderly woman with breast carcinoma Fig 15-41 Coronal (A) and axial (B) postcontrast T1-weighted MR scans in this 37-yearold man with end-stage acute myelogenous leukemia (AML) show subtle enhancing lesions in the cerebral sulci (arrows) Lumbar puncture disclosed AML in a subpial perivascular distribution produces innumerable tiny tumor nodules with a miliary appearing pattern (Fig 15-42).115 Parenchymal Metastases Parenchymal metastases are by far the most common CNS manifestation of extracranial primary neoplasms (see box) Etiology and pathology Etiology In descending order, the most common primary tumors to metastasize to brain are lung, breast, and malignant melanoma Gastrointestinal and genitourinary primary tumors represent fourth most common primary source.116 Pathology Grossly, parenchymal metastases are typically well-defined circumscribed nodules of varying size that can be solid or partially cystic (filled with mucinous material, necrotic debris, or hemorrhagic-fluid).2 Extensive perifocal edema is common and frequently , disproportionate to the size of the metastases focus.2 The microscopic appearance of metastases reflects the primary tumor source Age and incidence Parenchymal metastases are uncommon in children Intracerebral metastases in Chapter 15 Miscellaneous Tumors, Cysts, and Metastases Fig 15-42 Sagittal postcontrast T1-weighted MR scan in this patient with disseminated malignant melanoma shows innumerable tiny tumor nodules (arrows) in the vermis and occipital cortex Carcinomatous encephalitis adults are common, representing between one quarter and one third of all brain tumors 116,117 Brain metastases are found in 10% to 25% of autopsied patients with extracranial malignant neoplasms.116,118 Between 60% and 85% of metastases are multiple.118a Location All areas of the brain may be affected, but the corticomedullary junction is the most common site (Fig 15-43).2 Clinical presentation and natural history Clinical presentation varies from asymptomatic patients whose intracranial lesions are identified during evaluation for therapeutic protocols to nonambulatory patients with severe neurologic deficits Despite treatment with standard whole-brain radiation therapy, median survival time is a dismal to months.118 Aggressive treatments such as brachy- and neutron therapy, stereotactic gamma knife and linear accelerator radiosurgery, various radiationchemotherapy combinations, and surgical resection for solitary metastases have had mixed results and remain controversial Imaging Because detection of even a single brain metastasis in a cancer patient dramatically alters prognosis and may change therapy, the detection and characterization of cerebral metastases has received significant attention in the imaging literature.119 661 Fig 15-43 Axial gross pathology specimen of metastatic melanoma shows numerous hemorrhagic tumor implants (arrows) at the corticomedullary junction, the most typical site for parenchymal metastases from extracranial primary tumors (Courtesy B Horten.) Parenchymal Metastases Etiology Lung > breast > melanoma > GI/GU tumors Pathology Rounded solid/partially cystic mass ±edema Incidence Most common site of CNS metastases from extracranial primary tumor One quarter to one third of brain tumors 10% to 25% of autopsied cancer patients >80% multiple Age Rare in children, most common in older adults (>40 years) Location Anywhere; gray-white junction most common site Imaging NECT: iso/hyperdense; Ca+ + rare in untreated metastases CECT: strong solid/ring enhancement MR: most hypointense on T1-, hyperintense on T2WI; most enhance moderately intensely following contrast administration (dose of at least 0.1 mmol/kg recommended) 662 PART THREE Brain Tumors and Tumorlike Processes Fig 15-44 A, Axial NECT scan in this patient with breast carcinoma appears nearly normal A mass in the left basal ganglia (large arrow) is apparent only because the adjacent brain is edematous (small arrow) A hyperdense left occipital lesion (curved arrow) is present B, CECT scan shows numerous enhancing masses consistent with multifocal metastases Fig 15-45 A, Axial NECT scan in this middle-aged man with small cell lung cancer shows multifocal high density lesions (arrows) B, CECT scan shows numerous enhancing masses Note solid (large arrows), ring (curved arrow) and ependymal (small arrows) enhancing patterns Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 663 Fig 15-46 Axial NECT scans in this patient with melanoma show multiple high density lesions (arrows) Autopsy disclosed hemorrhagic metastases (compare with Fig 15-43) CT Attenuation of cerebral metastases on NECT scans varies Most metastases are isodense with adjacent brain (Fig 15-44) Hyperdense metastases are seen with small round cell tumors or other neoplasms with high nuclear to cytoplasmic ratios (Fig 15-45) Hemorrhage can occur in virtually any metastatic tumor, but renal and breast carcinomas, melanoma, and choroicarcinoma are the most likely metastases to bleed (Fig 15-46) Cystic (Fig 15-47) and calcified (Fig 15-48) untreated metastases are rare, representing approximately 1% to 6.6% of reported cases.120,120a Lung and breast carcinoma are the most common primary sources.120,121 Edema associated with metastases can be striking and in some cases is the only abnormality seen on NECT scans Most-but not all-parenchymal metastases enhance strongly following contrast administration Both solid and ringlike patterns are seen (Fig 15-45) Double-dose delayed CT scans significantly improve the sensitivity and specificity of cerebral metastatic disease detection.117 False-negative studies occur in 11.5% of patients if scans are obtained immediately following administration of the standard contrast dose.122 MR Signal intensity of brain metastases varies Most nonhemorrhagic intracerebral metastases are slightly hypointense relative to brain on T1-weighted scans (Fig 15-49, A).116 Some nonhemorrhagic metastases, most noticeably malignant melanoma, are often hyperintense on T1WI (Fig 15-50) T1 shortening in these cases correlates with melanin content, not hemorrhage or the presence of chelated metal ions.123 Fig 15-47 Axial CECT scan in this patient with adenocarcinoma of the lung shows a solitary thin-walled left occipital lobe mass (arrows) No other lesions were present, and the patient had no known metastases elsewhere Stereotactic biopsy disclosed metastatic tumor times and are therefore hyperintense on T2weighted sequences (Fig 15-49, B) Multifocal white matter and corticomedullary lesions on T2WI are common manifestations of metastatic disease (see Chapter 17) They therefore resemble the punctate high signal foci that are often observed on T2-weighted scans in normal elderly patients If multifocal hyperintense foci not enhance following con- 664 PART THREE Brain Tumors and Tumorlike Processes Fig 15-48 Axial pre- (A) and postcontrast (B) CT scans in this patient with untreated metastatic breast carcinoma show some of the lesions (arrows) are calcified Same case as Fig 15-44 Fig 15-49 A typical brain metastasis is demonstrated in this 47-year-old man with renal cell carcinoma and seizure A, Axial precontrast T1WI shows a tumor nodule (large arrow) that appears mixed iso- and slightly hypointense to adjacent brain Note gyral swelling and surrounding edema (small arrows) B, Axial T2WI shows the mixed signal lesion (large arrow) is mostly hyperintense to brain Note surrounding edema (small arrows) A second, subtle hyperintense focus is noted in the left frontal lobe (curved arrow) C, Following standard-dose contrast administration (0.1 mmol/kg), the tumor nodule (large arrow) enhance strongly The left frontal lesion (curved arrow) also enhances Several other metastases (arrowheads) are identified that were not apparent on the T2Wl Chapter 15 Miscellaneous Tumors, Cysts, and Metastases trast administration, the probability that they represent metastases rather than small vessel disease or other benign entities is low.119 Some metastatic tumors are hypointense on T2WI Examples are mucin-secreting neoplasms such as metastatic gastrointestinal adenocarcinoma.116 and densely cellular tumors with high nuclear to cytoplasmic ratios (Fig 15-51) Hemorrhage can also complicate the appearance of metastases (Fig 15-52; see Figs 7-50 to 7-52) Contrast-enhanced MR scans are the most sensitive imaging procedure for evaluating intracranial metastatic disease.117 Most-but not all-metastases enhance strongly following contrast administration Multifocal lesions located at the gray-white junction are typical (Fig 15-49, C) Solid, rim, and mixed- Fig 15-50 Axial T1-weighted MR scan in a patient with metastatic melanoma shows multifocal corticomedullary junction lesions (arrows) The lesions are hyperintense on this unenhanced study The lesions were not seen on the T2WI (not shown) (Courtesy J Stears.) 665 enhancement patterns occur (Fig 15-53) The optimum cost-effective contrast dosage has not been clearly established The standard contrast dose (0.1 mmol/kg) is adequate in most cases; low-dose studies (0.05 mmol/kg) are suboptimal (Fig 15-54) High-dose (0.2-0.3 mmol/kg) studies are even more sensitive than standard-dose (0.1 mmol/kg) examinations and may be helpful in detecting early, small, or additional metastatic lesions.124,125 In contrast to CT, delayed postcontrast studies not improve lesion-to-brain contrast.125 Limbic Encephalitis Paraneoplastic syndromes are defined as clinical manifestations associated with cancer that are not due to tumor in the affected organ126 (see box, p 666) Etiology and pathology Etiology The precise etiology of paraneoplastic syndromes is unknown, but autoimmune disorder and viral infection have been proposed as the most likely mechanisms.126 Small cell lung cancer (SCLC) is the extracranial malignancy most commonly associated with a range of neurologic paraneoplastic syndromes These include Lambert-Eaton myasthenic syndrome, subacute sensory neuropathy, myelopathy, cerebellar degeneration, and encephalopathy.127 Limbic encephalitis is a subacute encephalitis that predominately involves the limbic system and is frequently associated with malignant tumors, especially oat cell carcinoma.128,129 Other tumors associated with specific paraneoplastic syndromes include female genital tract tumors with cerebellar degeneration, neuroblastoma with opsoclonus, and Hodgkin's disease with demyelinating neuropathy.127 Pathology Gross abnormalities are usually absent, and biopsy findings are nonspecific Mononu- Fig 15-51 Metastatic germ cell tumor is seen in this 38-year-old man This densely cellular tumor (arrows) is hypointense on both T1- (A) and T2-weighted (B) scans 666 PART THREE Brain Tumors and Tumorlike Processes Fig 15-52 This 50-year-old man with no known primary tumor had decreasing mental status Axial T1- (A) and T2-weighted (B) MR scans show a right frontal lesion (large arrows) that is mostly isointense with cortex on both sequences A hypointense rim (open arrows) surrounds the mass Moderate peripheral edema (small arrows) is present Surgery disclosed extensive acute hemorrhage Underlying foci of metastatic hypernephroma were present on pathologic examination Limbic Encephalitis Paraneoplastic syndrome Clinical manifestations associated with cancer but not due to tumor in affected organ Etiology Unknown (?autoimmune/viral) Small cell lung cancer most commonl ssociate Fig 15-53 Axial postcontrast T1-weighted MR scan in this patient with squamous cell lung cancer shows a left frontal rim-enhancing mass This cystic metastasis resembles an abscess clear perivascular and parenchymal infiltrates with reactive gliosis, microglial proliferation, and neuronal loss have been reported.128,129 No tumor cells or viral inclusion bodies are present Incidence The exact incidence of paraneoplastic syndromes is unknown Limbic encephalitis has been identified in 2% to 3% of patients with SCLC.127 Age and gender The mean age of patients with SCLC is 64 years; nearly 80% of patients are men.127 Pathology Gross: usually normal/mild nonspecific temporal lobe swelling Microscopic: nonspecific inflammatory changes without viral indusions/tumor Incidence (Rare, 2% to 3% of patients with small cell lung cancers) Age and gender Older men most commonly affected by paraneoplastic syndromes; M = F in limbic encephalitis Location Limbic system (temporal lobes, insula, cingulate gyri) Imaging Nonspecific (indistinguishable from viral encephalitis, especially herpes) Chapter 15 Miscellaneous Tumors, Cysts, and Metastases 667 Fig 15-54 Contrast-enhanced T1-weighted MR scans in this patient with parenchymal metastases were performed using standard (0 mmol/kg) and low dose (0 05 mmol/kg) Multile lesions are clearly identified on the standard dose study (A, arrows) but are barely seen on the low dose sequence (B, arrows) (Courtesy W.T.C Yuh.) Fig 15-55 This 68-year-old man with known malignancy had decreasing mental status Axial T2-weighted MR scan (A) shows bitemporal hyperintense lesions (arrows) Postcontrast axial (B) and coronal (C) T1WI show extensive gyriform enhancement along both temporal lobes and the left insular cortex (arrows) CSF cytology disclosed pleocytosis but no malignant cells Biopsy showed nonspecific inflammatory changes, but no viral inclusions or tumor were identified Presumed limbic encephalitis 668 PART THREE Brain Tumors and Tumorlike Processes Reported cases of limbic encephalitis are equally divided between both genders.129 Location Hippocampal formations, amygdalae, and other medial temporal lobe structures are the most commonly involved sites in limbic encephalitis Other paraneoplastic syndromes affect different anatomic areas such as the cerebellum or spinal cord Clinical presentation and natural history The clinical hallmarks of limbic encephalitis are changing mental status with affective symptoms and memory impairment.129 Treatment of the primary malignancy may reverse the course of this syndrome in some cases Imaging Imaging findings are nonspecific CT scans are usually normal.128 High signal intensity in the medial temporal lobes can sometimes be identified on T2-weighted MR scans (Fig 15-55, A).129 Enhancement following contrast administration varies (Fig 15-55, B and C) The major differential diagnosis of limbic encephalitis is viral encephalitis (e.g., herpes encephalitis) REFERENCES AI-Ghamadi S, Black MJ, Lafond G: Extracranial head and neck schawannomas, J Otolaryngol 21:186-188, 1992 Okazaki H: Fundamentals of Neuropathology, ed 2, New York, Igaku-Shoin, 1989 Russell DS, Rubinstein LJ: Pathology of Tumors of the Nervous System, ed 5, Baltimore, Williams and Wilkins, 1989 Gentry LIZ, Mehta RC, Appen RE, Weinstein JM: MR imaging of primary trochlear nerve neoplasms, AJNR 12:707-713, 1991 Tung H, Chen T, Weiss MH: Sixth nerve schwannomas, J Neurosurg 75:638-641, 1991 Allcutt DA, Hoffman HJ, Isla A et al: Acoustic schwannomas in children, Neurosurg 29:14-18, 1991 McCormick PC, Bello JA, Post KD: Trigeminal schwannoma, J Neurosurg 69:850-860, 1988 Lizak PF, Woodruff WW: Posterior fossa neoplasms: multiplanar imaging, Sem US, CT, MR 13:182-206, 1992 Bilaniuk LT: Adult infratentorial tumors, Sem Roentgenol 25:155-173, 1990 10 Pollack IF, Sekhar LN, Jannetta PJ, Janecka IP: Neurilemmomas of the trigeminal nerve, J Neurosurg 70:737-745, 1989 11 Beges C, Revel MP, Gaston A et al: Trigeminal neuromas: assessment of MRI and CT, Neuroradiol 34:179-183, 1992 12.Brogan M, Chakeres DW: Gd-DTPA-enhanced MR imaging of cochlear schwannoma, AJNR 11:407-408, 1990 13 Liclov M, Som PM, Stacy C, Catalano P: Eccentric cystic facial schwannoma: CT and MR features, J Comp Asst Tomogr 15:1065-1067,1991 14 Martin N, Sterkers 0, Mompoint D, Nahum H: Facial nerve neuromas: MR imaging, Neuroradiol 34:62-67, 1992 15 Celli P, Ferrante L, Acqui M et al: Neurinoma of the third, fourth and sixth cranial nerves: a survey and report of a new fourth nerve case, Surg Neurol 38:216-224, 1992 16 Katsumata Y, Maehara T, Noda M, Shirouzu I: Neurinoma of the oculomotor nerve: CT and MR features, J Comp Asst Tomogr 14:662-664, 1990 17 Sigal R, D'Anthouard F, David P et al: Cystic schwannoma mimicking a brain stem tumor: MR features, J Comp tomogr 14:662-664, 1990 18 Casadei GP, Komori T, Scheithauer BW et al: Intracranial parenchymal schwannoma, J Neurosurg 79:217-222,1993 19 Burger PC, Scheithauer BW, Vogel FS: Surgical Pathology of the Nervous System and its Coverings, ed 3, New York, Churchill Livingstone, 1991 20.Abramowitz J, Dion JE, Jensen ME et al: Angiographic diagnosis and management of head and neck schwannona AJNR 12:977-984, 1991 21 Moscow NP, Newton TH: Angiographic features of hypervascular neurinomas of the head and neck, Radiol 114:635-640, 1975 22 Cohen LM, Schwartz AM, Rockoff SD: Benign schwannomma pathologic basis for CT inhomogeneities, AJR 147:141-143, 1986 22a Asari S, Katayama S, Itoh T et al: CT and MRI of haemorrhage into intracranial neuromas, Neuroradiol 35:247-250, 1993 23 Mulkens TH, Parizel PM, Martin J-J et al: Acoustic schwannoma: MR findings in 84 tumors, AJR 160-395-398, 1993 24 Vion-Dury J, Vincentelli F, Jiddane M et al: MR imaging of epidermoid cysts, Neuroradiol 29:333-338, 1987 25 Braun IF, Naidich TP, Leeds NE et al Dense intracranial dermoid tumors, Radiol 122:717-719, 1977 26 Ruge JR, Tomashitas T, Naidich TP et al Scalp and calvarial masses of infants and children, Neurosurg 22:1037-1042,1988 27 Gao P-Y, Osborn AG, Smirniotopoulos JG, Harris CP: Epidermoid tumor of the cerebellopontine angle, AJNR 13:863872, 1992 28 Wagle WA, Jaufmann B, Mincy JE: Magnetic resonance imaging of fourth ventricular epidermoid tumors, Arch Neurol 48:43840,1991 29 Bejarano PA, Burderick DF, Gado MH: Infected epidecyst of the sphenoid bone, AJNR 14:772-773, 1993 30.Pumar J, Otero E, Castfieira A et al: Intradiploic epidermoid tumor of the occipital bone X-ray, CT, MR finding; Eur Radiol 3:183-185, 1993 31 Tatler GLV, Kendall BE: The radiological diagnosis of epidermoid tumors, Neuroradiol 33(suppl):324-325, 1991 32 Tekkok IH, Cataltepe O, Saglam S: Dense epidermoid cyst the cerebellopontine angle, Neuroradiol 33:255-257,1991 33 Gualdi GF, Biasi C Di, Trasimeni G et al: Unusual MR and CT appearance of an epidermoid tumor, AJNR 12:771-772 1991 34 Tampieri D, Melanson D, Ethier R: MR imaging of epidermoid cysts, AJNR 10:351-356, 1989 35 Horowitz BL, Chari MV, James R, Bryan RN: MR in intracranial epidermoid tumors: correlation of in vitro imaging J, in vitro 13C spectroscopy, AJNR 11:299-302, 1990 36 Shen WC, Yang CF: Epidermoid cyst with variable contents shown on CT and MRI, Neuroradiol 33(suppl):317-318, 1991 37 Kawamura Y, Sze G: Totally cystic schwannoma of the cranial nerve mimicking an epidermoid, AJNR 134:13331334, 1992 38 Tsurucla JW, Chew CM, Moseley ME, Norman D: Diffusion weighted MR imaging of the brain: value of differentiating between extraaxial cysts and epidermoid tumors, AJNR 11:925-931, 1990 39 Smith AS: Myth of the mesoderm: ectodermal origin of dermoids, AJNR 10:449, 1989 40 Smith AS, Benson JE, Blaser Sl et al: Diagnosis of ruptured intracranial dermoid cyst: value of MR over CT, AJNR 12:175-180, 1991 41 Wilms G, Casselman J, Demaerel Ph et al: CT and MRI of uptured intracranial dermoids, Neuroradiol 33:149-151, 1991 41a Markus H, Kendall BE: MRI of a dermoid cyst containing hair, Neuroradiol 35:256-257, 1993 Chapter 15 Lunardi P, Missori P: Supratentorial dermoid cysts, J Neurosurg 75:262-266, 1991 43.Searce TA, Shaw C-M, Bronstein AD, Swanson PD: Intraventricular fat from a ruptured sacral dermoid cyst: clinical, radiographic, and pathological correlation, J Neurosurg 78:666-668, 1993 44.Ahmad I, Tominaga T, Ogawa A, Yoshimoto T: Ruptured suprasellar dermoid associated with middle cerebral artery aneurysm case report, Surg Neurol 38:341-346, 1992 45.Rubin G , Scienza R, Pasqualin A et al: Crartiocerebral epidermoids and dermoids, Acta Neurochir (Wien) 97:1-16, 1989 46.Drolshagen LF, Standefer M: Dense dermoid cyst of the posterior fossa, AJNR 12:317, 1991 47.Ulno A, Hasuo K, Matsumoto S, Masuda K: Solitary choroid plexus lipomas: CT and MR appearance, AJNR 14:116 1993 48.Rorke LB: Demystifying malformations, AJNR 11:675, 1990 49.Truwitt CL, Barkovich AJ: Pathogenesis of intracranial lipoma: an MR study in 42 patients, AJNR 11:665-674, 1990 50.Tart RP, Quisling RG: Curvilinear and tubulonodular varieties of lipoma of the corpus callosum: an MR and CT study, Compt Asst Tomogr 15:805-810, 1991 50a Britt PM, Bindal AK, Balko MG, Yeh H-SH: Lipoma of the cerebral cortex: case report, Acta Neurochir (Wieh) 121:88-92 1993 51.Donati F, Vassella F, Kaiser G, Blumberg A: Intracranial lipomas, Neuropediatr 23:32-38, 1992 52.RDuhart F, Goas JY, Neriot P, Zagnoli F: Le lipome du corps calleux, Sem Hop Paris 68:331-335, 1992 53.Eghwrudjakpor PO, Kurisaka M, Fukuoka M, Mori K: Intracranial lipomas, Acta Neurochir (Wien) 110:124-128, 1991 54.Nhfin GI, Keller MS: Pericallosal lipoma extending through the choroidal fissure: US/CT/MRI correlation, Neuroradiol 34:402-403, 1992 55.Uchino A, Hasuo K, Matsumoto S, Masuda K: MRI of dorsa mesencephalic lipomas, Clin Imaging 17:12-16, 1993 56.Wolpert SM, Barnes PD: Encephalocraniocutaneous lipoma t6sis In MRI in Pediatric Neuroradiology, p 329, St Louis Mosby Year-Book, 1992 57.Cohen TI, Powers SK, Williams DW III: MR appearance of intracanalicular eighth nerve lipoma, AJNR 13:1188-1190 1992 58.Belfinger C, Saule H: Imaging of lipoma of the corpus callosum and intracranial dermoids in the Goldenhar syndrome Pediatr Radiol 18:72-73, 1988 59.Dean B, Drayer BP, Berisini DC, Bird CR: MR imaging of pericallosal lipoma, AJNR 9:929-931, 1988 60.Georgy BA, Hessilink JR, Jernigan TL: MR imaging of the corpus callosum, AJR 160:949-955, 1993 61.van Burken, Sarioglu AC, O'Donnell HD: supratentorial arachnoidal cyst with intracystic and subdural hematoma Neurochir 35:199-203, 1992 62.LuAacc S, Toland J, Stack J: CT and MRI of arachnoid cyst with complicating intracystic and subdural hemorrhage, J Comp Asst Tomogr 16:995-997, 1992 62a Garcia Santos JM, Martinez-Lage J, Ubeda AG et al: Arachnoid cysts of the middle fossa: a consideration of their origins based on imaging, Neuroradiol 39:395-358, 1993 63.Becker T, Wagner M, Hofmann E et al: Do arachnoid cyst grow? A retrospective CT volumetric study, Neuroradiol 33:341-345, 1991 64.Flodmark 0: Neuroradiology of selected disorders of the menengis, calvarium and venous sinuses, AJNR 13:483-491 1992 65.Robertson SJ, Wolpert SM, Runge VM: MR imaging of middle cranial fossa arachnoid cysts: temporal lobe agenesis syndrome revisited, AJNR 10:1007-1010, 1989 66.Ciricillo SF, Cogen PH, Harsh GR, Edwards MSB: Intracra- Miscellaneous Tumors, Cysts, and Metastases 669 nial arachnoid cysts in children: a comparison of the effects of fenestration and shunting, J Neurosurg 74:230-235, 1991 67 Wester K: Gender distribution and sidedness of middle fossa arachnoid cysts: a review of cases diagnosed with computed imaging, Neurosurg 31:940-944, 1992 68 Dhooge C, Govaert P, Martens F, Caemaert J Transventricular endoscopic investigation and treatment of suprasellar arachnoid cysts, Neuropediatrics 23:245-247, 1992 68a Garcia Santos JM, Martinez-Lage J, Gilabert Ubeda A et al: Arachnoid cysts of the middle cranial fossa: a consideration of their origins based on imaging, Neuroradiol 35:355-358, 1993 69.Quint DJ: Retroclival arachnoid cysts, AJNR 13:1503-1504, 1992 70 Tien RD, MacFall J, Heinz ER: Evaluation of complex cystic masses of the brain: value of steady-state free-precession MR imaging, AJR 159:1049-1055, 1992 71 Maeda M, Kawamura Y, Tamagawa Y et al: Intravoxel incoherent motion (IVIM) MRI in intracranial, extraaxial tumors and cysts, J Comp Asst Tomogr 16:514-518, 1992 72.Kondziolka D, Bilbao JM An immunohistochernical study of neuroepithelial (colloid) cysts, J Neurosurg 71:91-97, 1989 73 Lach B, Scheithauer BW, Gregor A, Wick MP: Colloid cyst of the third ventricle: a comparative immunohistochernical study of neuraxis cysts and choroid plexus epithelium, J Neurosurg 78:101-111, 1993 74.Waggenspack GA, Guinto FC Jr: MR and CT of masses of the anterosuperior third ventricle, AJNR 10:105-110, 1989 75.Hine AL, Chui MS: Hypodense colloid cyst of the third ventricle, J Can Assoc Radiol 38:288-291, 1987 76 Shuangshoti S, Pitakdamrongwong N, Poneprasert B et al Symptomatic neuroepithelial cysts in the posterior cranial fossa, Surg Neurol 30:298-304, 1988 77.Sener RN, Jinkins JR: CT of intrasellar colloid cysts, J Comp Asst Tomogr 15:671-672, 1991 78 Mathiesen T, Grane P, Lindquist C, von Holst H: High recurrence rate following aspiration of colloid cysts in the third ventricle, J Neurosurg 78:748-752, 1993 79 Wilms G, Marchal G, Van Hecke P et al: Colloid cysts of the third ventricle: MR findings, J Comp Asst Tomogr 14:527-531, 1990 80.Crenshaw WB, Chew FS: Rathke's cleft cyst, AJR 158:1312, 1993 81 Ross DA, Norman D, Wilson CB: Radiologic characteristics and results of surgical management of Rathke's cysts in 43 patients, Neurosurg 30:173-179, 1992 82 Voelker JL, Campbell RL, Muller J: Clinical radiographic and pathological features of Rathke's cleft cysts, J Neurosurg 74:535-544, 1991 83.Itoh J, Usui K: An entirely suprasellar symptomatic Rathke's cleft cyst: case report, Neurosurg 30:581-585, 1992 83a.Whyte AM, Sage MR, Brophy BP: Imaging of large Rathke's cleft cysts by CT and MRI: report of two cases, Neuroradiol 35:258-260, 1993 94 Hua F, Asato R, Miki Y et al: Differentiation of suprasellar nonneoplastic cysts from cystic neoplasms by Gd-DTPA MRI, J Comp Asst Tomogr 16:744-749, 1992 85 Numaguchi Y, Foster RW, Gum GK: Large symptomatic noncolloid neuroepithelial cysts in the lateral ventricle: CT and MR features, Neuroradiol 31:98-101, 1989 86.Nakase H, Ishida Y, Tada T et al: Neuroepithelial cysts of the lateral ventricle, Surg Neurol 37:94-100, 1992 87 Sherman JL, Camponovo E, Citrin CM: MR imaging of CSFlike choroidal fissure and parenchymal cysts of the brain, AJNR 11:939-945, 1990 88.Ciricillo SF, Davis RL, Wilson CB: Neuroepithelial cysts of the posterior fossa, J Neurosurg 72:302-305, 1990 89.Numaguchi Y, Kumra A, Schmidt RD, Martino C: Noncol- 670 PART THREE Brain Tumors and Tumorlike Processes loid neuroepithelial cysts in the lateral ventricles: magnetic resonance features, CT: J Comp Tomogr 12:174-181, 1988 90 Wilkins RH, Burger PC: Benign intraparenchymal brain cysts without an epithelial lining, J Neurosurg 68:378-382, 1988 91 Ito S, Fujiwara S, Mizoi K et al: Enterogenous cysts at the cer- ebellopontine angle: case report, Surg Neurol 37:366-370, 1992 92 Gao P-Y, Osborn AG, Smirniotopoulos JG et A Intraspinal and posterior fossa enterogenous cysts: imaging and pathologic spectrum, AJNR, in press 93 Brooks BS, Durall ER, El Garnmal T et al: Neuroirnaging features of neurenteric cysts: analysis of nine cases and review of the literature, AJNR 14:735-746, 1993 94 Malcolm GP, Symon L, Kendall B, Pires M: Intracranial neurenteric cysts, J Neurosurg 75:115-120, 1991 95 Elster AD: Modern imaging of the pituitary, Radiol 187:1-14, 1993 95a Elster AD: Imaging of the sella: anatomy and pathology, Sem US, CT, MR 14:182-194, 1993 96.Johnsen DE, Woodruff WW, Allen IS et A MR imaging of the sellar and juxtasellar regions, RadioGraphics 11:727-758, 1991 97 Schwartzberg DG: Imaging of pituitary tumors, Sem US, CT, MR 13:207-223, 1992 98 Hall WA, Luciano MG, Doppman JL et al: A prospective double-blind study of high resolution pituitary MRI in normal human subjects: occult pituitary adenomas in the general population, J Neurosurg 72:342A, 1990 99 Schubiger O, Haller D: Metastases to the pituitary hypothalamic axis, Neuroradiol 34:131-134, 1992 100.Juneau P, Schoene WC, Black P: Malignant tumors in the pituitary gland, Arch Neurol 49:555-558, 1992 101.Popovic EA, Vattuone JR, Siu KH et al: Malignant prolacti- nomas, Neurosurg 29:127-130, 1992 102.Lundin P, Nyman R, Burmas P et al: MRI of pituitary neuroadenomas with reference to hormonal activity, Neuroradiol 34:43-51, 1992 102a Bartuska DG, Kleinman DS, Kodroff KS, Piatok DJ: The sellar/parasellar endocrinopathies: a brief clinical overview, Sem US, CT, MR 14:178-181, 1993 102b Davis DH, Laws ER Jr, Ilstrup DM et al: Results of surgical treatment for growth hormone-secreting pituitary adenomas, J Neurosurg 79:70-75, 1993 102c Yamada S, Aita T, Sano T et al: Growth hormone-producing pituitary adenomas: correlations between clinical characteristics and morphology, Neurosurg 33:20-27, 1993 103.Hsu DW, Hakim F, Biller BMK et al: Significance of proliferating cell nuclear antigen index in predicting pituitary adenoma recurrence, J Neurosurg 78:753-761, 1993 103a Bonneville J-F, Cattin F, Gorczyca W, Hardy J: Pituitary microadenomas: early enhancement with dynamic CT implications of arterial blood supply and potential importance, Radiol 187:857-861, 1993 103b Dina TS, Feaster SH, Laws ER Jr, Davis DO: MR of the pituitary gland postsurgery: serial MR studies following transsphenoidal resection, AJNR 14:763-769, 1993 104.Lundin P, Bergstrom K, Nyman R et al: Macroprolatinomas: serial MR imaging in long-term bromocriptine therapy, AJNR 13:1279-1291, 1992 105.Zimmerman RA: Imaging of intrasellar, suprasellar and parasellar tumors, Sem Roentgenol 25:174-197, 1990 106.Hoffman HJ, de Silva M, Humphries RP et al: Aggressive surgical management of craniopharyngiomas in children, J Neurosurg 76:47-52, 1992 106a Demaerel P, Moseley IF, Scaravilli F: Recurrent craniopharyngioma invading the orbit, cavernous sinus, and skull base: a case report, Neuroradiol 35:261-263, 1993 107.Ahmadi J, Destian S, Apuzzo MLJ et al: Cystic fluid in craniopharyngiomas: MR imaging and quantitative analysis, Radiol 182:783-785, 1992 107a Hershey BL: Suprasellar masses: diagnosis and differential diagnosis, Sem US, CT, MR 14:215-231, 1993 108.West MS, Russell EJ, Breit R et al: Calvarial and skull base metastasis: comparison of nonenhanced and Cd-DTPAenhanced MR images, Radiol 174:85-91, 1990 109 Buff BL Jr, Schick RM, Norregaard T: Meningeal metastasisof leiomyosarcoma mimicking meningioma: CT and MR findings, J Comp Asst Tomogr 15:166-167, 1991 110.Tyrrell RL, Bundschuh CV, Modic MT: Dural carcinomatosis: MR demonstration, J Comp Asst Tomogr 11:329-332,1987 111.Sze G, Soletsky S, Bronen R, Krol G: MR imaging of the cranial meninges with emphasis on contrast enhancement and meningeal carcinomatosis, AJNR 10:965-975, 1989 112.Sze G: Diseases of the intracranial meninges: MR imaging features, AJR 160:727-733, 1993 113.Rodesch G, Van Bogaert P, Mavroudakis N et A Neuroradiologic findings in leptomeningeal carcinomatosis: the value interest of gadolinium-enhanced MRI, Neuroradiol 32:26-32, 1990 114.Olsen WL, Winkler ML, Ross DA: Carcinomatous encephalitis: CT and MR findings, AJNR 8:553-554, 1987 115.Nemzek W, Poirier V, Salamat MS, Yu T: Carcinomatous encephalitis (miliary metastases): lack of contrast enhance AJNR 14:540-542, 1993 116.Egelhoff JC, Ross JS, Modic MT et al: MR imaging of meta- static GI adenocarcinoma in brain, AJNR 13:1221-1224,1992 117.Davis PC, Hudgins PA, Peterman SB, Hoffman JC Jr: Dignosis of cerebral metastases: double-dose delayed CT vs contrast-enhanced MR imaging, AJNR 12:293-300, 1991 118.Smalley SR, Laws ER Jr, O'Fallon JR et al: Resection for solitary brain metastasis, J Neurosurg 77:531-540, 1992 118a Bindal RK, Sawaya R, Leavens ME, Lu JJ: Surgical treatment of multiple brain metastases, J Neurosurg 79:210-216, 199 119.Elster AD, Chen MYM: Can nonenhancing white matter lesions in cancer patients be disregarded? AJNR 13:13091315, 1992 120.Fukuda Y, Homma T, Kohga H et al: A lung cancer case the numerous calcified metastatic nodules of the brain, Neuroradiol 30:265-268, 1988 120a Hwang T-L, Valdivieso JG, Yang C-H, Wolin MJ: Calcified brain metastasis, Neurosurg 32:451-454, 1993 121.Yamazaki T, Harigaya Y, Naguchi O et A Calcified miliary brain metastases with mitochondrial inclusion nodules of the brain, J Neurol Neurosurg Psychiatr 56:110-111, 1993 122.Shalen PR, Hayman LA, Wallace S et al: Protocol for delayed contrast enhancement in computed tomography of cerebral neoplasia, Radiol 139:397-401, 1981 123.Atlas SW, Braffman BH, LoBuitto R et al: Human malignant melanomas with varying degrees of melanin in nude mice MR imaging, histopathology, and electron paramagnetic resonance, J Comp Asst Tomogr 14:547-554, 1990 124.Yuh WTC, Engelken JD, Muhonen MG et A Experience with high-dose gadolinium MR imaging in the evaluation of brain metastases, AJNR 13:335-345, 1992 125.Haustein J, Laniado M, Nienclorf H-P et al: Triple-dose versus standard-dose gadopentetate dimeglumine: a randomized study in 199 patients, Radiol 186:855-860, 1993 126.Hansen RA, Urich H: Cancer and the Nervous System pp, 311-621, Oxford, Blackwell Scientific, 1982 127.Elrington GM, Murray NMF, Spiro SG, Newsom-Davis J: Neurological paraneoplastic syndromes in patients, with small cell lung cancer: a prospective survey of 150 patients, J Neurol Neurosurg Psychiatr 54:764-767, 1991 128.Lacomis D, Koshbin S, Schick RM: MR imaging of paraneoplastic limbic encephalitis, J Comp Asst Tomogr 14:115- 1990 129.Kodama T, Numagredri Y, Gella FE et A Magnetic resonance imaging of limbic encephalitis, Neuroradiol 33:520-523, 1991 .. . gadolinium-enhanced MRI, Neuroradiol 32:26-3 2, 1990 114.Olsen WL, Winkler ML, Ross DA: Carcinomatous encephalitis: CT and MR findings, AJNR 8:553-55 4, 1987 11 5. Nemzek W, Poirier V, Salamat MS, Yu T: Carcinomatous .. . analysis, Radiol 182:783-78 5, 1992 107a Hershey BL: Suprasellar masses: diagnosis and differential diagnosis, Sem US, CT, MR 14: 215- 23 1, 1993 108.West MS, Russell EJ, Breit R et al: Calvarial and. .. Timothy J Miller.) 630 PART THREE Brain Tumors and Tumorlike Processes cystic degeneration are common in larger lesions (Figs 157 2, C and 15- 3, Q, but frank hemorrhage is rare (Fig 15- 3, A ).2 2a Nearly