748 SECTION VI Pediatric Critical Care Neurologic Intracranial Hemorrhage and Vascular Malformations Intracranial hemorrhage can be readily detected using noncon trast CT or MRI with SWI and GRE seque[.]
748 S E C T I O N V I Pediatric Critical Care: Neurologic Intracranial Hemorrhage and Vascular Malformations aneurysms, and generally will be required before surgical or endovascular intervention In the appropriate clinical setting, however, such as a spontaneous SAH without etiology, a negative MRI, MRA, or CTA should not exclude a catheter angiogram Arterial aneurysms are much less common in children than in adults, with many of those seen likely being congenital or due to infection in contrast to the typical acquired berry aneurysms seen in adults As in adults, all but the smallest aneurysms can be seen on MRA or CTA, with CTA sensitivity for berry aneurysms in adult series reported in the range of 80% to 97%.18 These studies, though, need to be of optimum resolution, are generally targeted to the high-risk locations for aneurysms in adults, and may not include less common aneurysm locations, which are seen with greater frequency in children Angiographically occult lesions—including capillary telangiectasia, cavernous malformation, and developmental venous anomalies—are seen on MRI but usually are not of consequence except in cases of the occasional large cavernous malformation A vein of Galen aneurysmal malformation (VGAM) is a misnomer because it is not the vein of Galen but rather is a persistent embryonic vein that is dilated in association with a large fistula.42 Intracranial hemorrhage can be readily detected using noncontrast CT or MRI with SWI and GRE sequences The presence of nontraumatic intracranial hemorrhage could indicate hemorrhagic conversion of an ischemic stroke, underlying coagulopathy, hemorrhagic neoplasm, or vascular malformation A large study found an incidence of hemorrhagic stroke of 1.4 per 100,000 person years in those younger than 20 years of age An underlying aneurysm was found in 13%, including 57% of those with pure SAH, 2% of those with a pure parenchymal hemorrhage, and 5% of those with a mixed hemorrhage.41 Etiologic workup of hemorrhagic stroke in children includes a broad differential In the setting of hemorrhagic stroke of unknown obvious cause, MRA and CTA are important imaging tests Most arteriovenous malformations and aneurysms can be detected with a combination of MRI and MRA or CTA, although small lesions can be missed (Fig 61.14) Catheter angiogram remains the gold standard for arteriovenous malformation diagnosis, confirming flow dynamics and the presence of intranidal A R A L P B C • Fig 61.14 A 14-year-old child with a left occipital arteriovenous malformation (AVM) (A) Axial T2weighted magnetic resonance imaging shows multiple flow voids in the left occipital lobe (arrow) (B) Lateral view from catheter angiogram confirms the presence of an AVM (arrow) and early draining veins (curved arrow) (C) Lateral maximum-intensity projection image from a magnetic resonance angiogram shows an enlarged posterior cerebral artery branch (arrows), which feeds the tangle of abnormal vessels 749 CHAPTER 61 Neuroimaging S A A B C P I • Fig 61.15 Vein of Galen aneurysmal malformation (A) Axial noncontrast computed tomography scan shows the dilated embryonic vein (arrows) Axial T2 (B) and sagittal T1 (C) magnetic resonance imaging demonstrates the dilated embryonic vein (arrows) and the draining vein (arrowheads) VGAMs presenting in the newborn period can manifest with cardiac symptoms resulting from the large shunt and high-output congestive cardiac failure VGAM can be identified on cranial ultrasound and head CT (Fig 61.15) In the presence of a VGAM, MRI with MR angiography will give an overall vascular road map for planning endovascular intervention, because the limited amount of iodinated contrast that can be used in a neonate necessitates directed intervention Venous Infarct Dural venous sinus thrombosis and venous infarct can produce a range of clinical presentations ranging from headache due to intracranial hypertension to herniation syndromes, such as those related to intraparenchymal hemorrhage Intraparenchymal hemorrhage or imaging evidence of edema in a nonarterial distribution raises suspicion of a venous stroke In the setting of suspected dural venous sinus thrombosis or venous stroke, evaluation of the cerebral venous system should be undertaken Ultrasound has limited utility in this setting, although evaluation of superior sagittal sinus flow can be undertaken in the young infant with an open fontanelle CT evidence of a venous clot can be detected as hyperdense venous sinuses acutely on noncontrast scans and as the empty delta sign (lower density in area of clot surrounded by enhancing blood) in the superior sagittal sinus on contrast-enhanced scans This assessment can be problematic in the newborn in whom the normal low-density unmyelinated brain and typically higher hematocrit make the venous sinuses appear dense normally on CT Classically, the venous phase of a catheter angiogram has been used to look for venous sinus thrombosis Catheter evaluation of the venous sinuses, however, has been effectively replaced with MRV techniques MRV uses flow-sensitive sequences that can delineate the major venous sinuses quite effectively without the need for IV contrast (see Fig 61.5) A subacute clot in a venous sinus also can be evident on standard T1- and T2-weighted MRI as bright areas in the venous sinuses, although an acute clot can be more difficult to appreciate On MRI, GRE and SWI sequences may demonstrate low signal, and T1 contrast-enhanced sequences may demonstrate areas of nonenhancement of thrombosed venous sinuses • Fig 61.16 Posterior reversible encephalopathy syndrome Axial fluidattenuated inversion recovery magnetic resonance imaging showing subcortical foci of hyperintensity (arrows) associated with cyclosporin toxicity Note that abnormalities may have a variable distribution and are frequently, but not always, posterior in location Posterior Reversible Encephalopathy Syndrome Posterior reversible encephalopathy syndrome (PRES) results from a loss of autoregulation in the older infant and child as seen in hypertensive encephalopathy, cytotoxic and immunosuppressive drug neurotoxicity, and thrombotic thrombocytopenia purpura Typically, PRES preferentially involves a posterior and parasagittal distribution of the brain with T2 and FLAIR hyperintensities and, less frequently, can involve the frontal lobes and brainstem.43,44 Lesions often are relatively symmetric, confluent, centered in the subcortical white matter, and, rarely, demonstrate patchy enhancement (Fig 61.16) Frequently, because the underlying pathology causes only vasogenic edema, these lesions will not be restricted on DWI However, ischemia can be triggered by 750 S E C T I O N V I Pediatric Critical Care: Neurologic III * A * B C • Fig 61.17 Obstructive hydrocephalus Axial (A) and midline sagittal (B) T2 magnetic resonance imaging (MRI) shows dilated lateral (asterisks) and third (III) ventricles that result from aqueductal obstruction (arrow) (C) Chiari II malformation with hydrocephalus Image demonstrates utility of heavily T2-weighted, halfFourier acquisition, single-shot, turbo spin-echo MRI in evaluation of ventricles Sequence can be obtained rapidly without the need for sedation; this avoids the radiation associated with repeated computed tomography scans a severe increase in blood pressure, resulting in superimposed cytotoxic edema and therefore diffusion-restricted lesions that usually result in infarctions, the severity of which often correlates with prognosis In children, PRES can have less typical imaging patterns than those observed in adults Central Nervous System Infection Imaging findings and the role of imaging in cerebral infection will depend on the organism and location of the infection.45,46 The appearance will also depend on the cell type infected and the host immune response Infection can involve the subarachnoid spaces and meninges, parameningeal spaces, or the brain parenchyma itself, either primarily or secondarily With bacterial meningitis the appearance on CT and MRI may range from normal to diffuse swelling with loss of gray-white differentiation and obliteration of ventricular and cisternal CSF spaces Coxsackievirus, echovirus, and mumps infect the meninges more than the neurons, whereas poliovirus infects the neurons, particularly the motor neurons Herpes simplex virus type has a predilection for the limbic system, most commonly affects the temporal lobes, and is the most common sporadic viral encephalitis.47 Herpes simplex virus type encephalitis is most commonly acquired at birth and does not display a predilection for the temporal lobes Although MRI is more sensitive than CT, a normal MRI still does not entirely exclude viral encephalitis In the clinical setting of suspected meningeal infection, CT may be indicated prior to lumbar puncture to exclude hydrocephalus or swelling that potentially would preclude lumbar puncture without neurosurgical consultation Imaging alone should not be used to exclude meningeal infection, however Particularly early in the setting of meningitis, contrast-enhanced CT is often normal Although MRI with gadolinium is more sensitive, only 55% to 70% of persons with proved meningitis have abnormal CT or MRI scans.8 Some investigators believe that CSF hyperintensity on the FLAIR sequence is more sensitive than gadolinium-enhanced T1-weighted sequence for meningitis However, CSF hyperintensity on FLAIR associated with supplemental oxygen and anesthesia as well as noninfectious meningeal irritation and leptomeningeal tumor render this finding less specific.48,49 Complications associated with meningeal infection include compromise of the BBB leading to vasogenic edema, arterial spasm that can cause ischemia with cytotoxic edema and eventual infarction, and hydrocephalus potentially with the development of transependymal CSF flow/interstitial edema Hydrocephalus can be obstructive, typically at the level of the cerebral aqueduct (Fig 61.17) or outlet of the fourth ventricle, or more commonly communicating because of impaired CSF resorption from arachnoid granulation obstruction with exudates This impairment of CSF resorption can become permanent because of leptomeningealependymal fibrosis and require shunting Ultrasound can be used in very young patients; otherwise, CT and more recently half Fourier acquisition single-shot turbo spin echo (HASTE) or other rapid, heavily T2-weighted MRI sequences usually are used to follow ventricular dilation A primary role for imaging in meningitis is to evaluate for these complications Two patterns of abnormal meningeal enhancement are seen on MRI with meningitis A pachymeningeal pattern appears as diffuse linear thickening of the normal dural lining However, this appearance is not specific because the same pattern can be seen in other settings, including after surgery and occasionally following shunt revision, in some cases because of intracranial hypotension The other pattern is a leptomeningeal enhancement in which enhancement is seen along the pia-arachnoid membranes following the sulcal grooves This pattern also is not specific, with a similar appearance being seen at times with leptomeningeal spread of tumor Extraaxial collections can develop in association with meningitis, including subdural effusions and, less commonly, subdural abscesses or empyema Effusions are crescentic collections that typically are isodense to CSF on CT and isointense to CSF on most MRI sequences, although because the protein level may be increased, the collections may be hyperintense on T1 and FLAIR (Fig 61.18) Subdural abscesses can be crescentic or lentiform when larger and typically slightly denser than CSF on CT A rim CHAPTER 61 Neuroimaging 751 • Fig 61.18 Chronic subdural effusions following meningitis Axial T2weighted magnetic resonance imaging shows mass effect with sulcal compression associated with bifrontal subdural collections (arrows) Note that these subdural collections can be differentiated from enlarged subarachnoid spaces because the latter would have bridging vessels crossing the cerebrospinal fluid in the subarachnoid spaces of enhancement of variable thickness is generally better detected on MRI (Fig 61.19) DWI can demonstrate restricted diffusion in subdural empyemas due to the relatively restricted movement of water molecules in purulent material Subdural (and brain) abscess also can occur as a direct extension of paranasal sinus or mastoid infection Infection of the brain parenchyma can take the form of an abscess or a more diffuse encephalitis Encephalitis in isolation or associated with meningitis generally will produce nonspecific cerebral parenchymal changes or cerebritis that appear bright on T2 and FLAIR sequences Differentiation by imaging of cerebritis from ischemic changes associated with meningoencephalitis is problematic, especially because cerebritis also can demonstrate restricted diffusion Areas of cerebritis evolve into focal abscesses that will generally demonstrate a central focus of low density on CT and low T1, high T2, and FLAIR signal on MRI, with a ring of enhancement and variable surrounding edema (Fig 61.20) More commonly in adults with a ring-enhancing lesion, there can be uncertainty in differentiating between a brain abscess and necrotic tumor The brain abscess generally will have a thinner rim of enhancement, and on DWI a pyogenic abscess will demonstrate restricted diffusion The necrotic tumor often shows a thick, irregular rim with increased diffusion or T2 shine-through In differentiating pyogenic, tubercular, and fungal abscesses, some studies have described a greater likelihood of homogeneous diffusion restriction with pyogenic and tubercular abscesses but a variable pattern with fungal abscesses.50,51 Exclusion of a meningeal or parameningeal abscess in the head can be accomplished largely with contrast-enhanced CT, looking for a fluid collection • Fig 61.19 Subdural abscess or subdural empyema Axial T1-weighted magnetic resonance imaging with gadolinium demonstrates a small rimenhancing right frontal paramedian subdural abscess (arrows) This area was restricted on diffusion-weighted imaging (not shown) with a surrounding enhancing rim, although occasionally a small collection may be missed on CT but detected by MRI Evaluation for meningeal or parameningeal abscess in the spine should be approached with MRI Demyelinating Disease Multiple sclerosis (MS) is much less common in children than in adults, whereas ADEM primarily occurs in children ADEM can manifest with symmetric involvement of central gray matter at times (Fig 61.21), with an imaging picture that overlaps with some metabolic diseases In other cases of ADEM, lesions, typically in the cerebral white matter, can be scattered with a picture similar to vasculitis or embolic infarction The appearance of MS and ADEM can be similar, though some features, such as the perivenule orientation (Dawson fingers) of lesions, are more characteristic of MS The presence of lesions of multiple ages would be consistent with MS (Fig 61.22) rather than ADEM Demyelinating lesions are seen most commonly in white matter but appear in gray matter as well Acute demyelinating lesions demonstrate enhancement Acute lesions also can demonstrate restricted diffusion, with an appearance on DWI that mimics an acute ischemic lesion Often, however, the pattern of involvement is useful in distinguishing demyelinating disease from ischemic disease The spinal cord can be involved with MS or ADEM (Fig 61.23), although relatively rarely in isolation Hence, imaging the brain to look for additional involvement can be useful in some cases to distinguish between a cord demyelinating process and infarct, which can have a similar imaging appearance 752 S E C T I O N V I Pediatric Critical Care: Neurologic A B C D • Fig 61.20 Frontal brain abscesses (A) Axial T2-weighted magnetic resonance imaging (MRI) demonstrates a right frontal ring-enhancing lesion with a T2 hypointense capsule that has considerable surrounding vasogenic edema and leftward midline shift The lesion is bright on diffusion (B) and dark on the apparent diffusion coefficient map (C), suggesting that it is diffusion restricted (D) In another patient, axial postcontrast T1-weighted MRI demonstrates a right frontal periventricular ring-enhancing lesion with T1 hypointense vasogenic edema surrounding it Trauma CT remains the primary imaging modality in persons with acute traumatic brain injury (TBI) and has the advantage of relative ease of scanning compared with MRI, including speed of scanning and allowing non-MRI-compatible monitoring and life support equipment to be used during imaging CT is usually sufficient for evaluation of most TBI requiring intervention, including assessment of swelling and acute hemorrhage within the intraaxial and extraaxial compartments CT is generally more sensitive than MRI in detecting acute SAH and in the evaluation of bony injury (Fig 61.24) CT is generally sufficient to detect cerebral swelling associated with herniation syndromes and therefore can identify the potential need for neurosurgical intervention (Fig 61.25) MRI is more sensitive for the detection of parenchymal injury and for more subtle extraaxial collections, including more chronic subdural hematomas, a hallmark of abusive head trauma associated with child abuse MRI is indicated when there is doubt as to the presence of a subdural blood collection in the setting of suspected trauma Also, in the setting of abusive head trauma, MRI can detect evidence of old parenchymal or extraaxial hemorrhage not seen with CT using the GRE sequence (see Fig 61.8D) In particular, gradient sequences and susceptibilityweighted imaging can reveal evidence of old parenchymal hemorrhages Bony injury of the spine is better evaluated with CT, although cord compression and injury are better assessed with MRI ... on MRI with meningitis A pachymeningeal pattern appears as diffuse linear thickening of the normal dural lining However, this appearance is not specific because the same pattern can be seen in... brain abscess generally will have a thinner rim of enhancement, and on DWI a pyogenic abscess will demonstrate restricted diffusion The necrotic tumor often shows a thick, irregular rim with increased... midline sagittal (B) T2 magnetic resonance imaging (MRI) shows dilated lateral (asterisks) and third (III) ventricles that result from aqueductal obstruction (arrow) (C) Chiari II malformation