715CHAPTER 59 Critical Care Considerations for Common Neurosurgical Conditions Management Surgical intervention for arachnoid cysts is reserved for cases with progressive growth or concerning mass eff[.]
CHAPTER 59 Critical Care Considerations for Common Neurosurgical Conditions Management Surgical intervention for arachnoid cysts is reserved for cases with progressive growth or concerning mass effect Asymptomatic small lesions that not enlarge are generally left untreated, regardless of their location and size When an operation is indicated, fenestration into an adjacent cistern is often performed, followed by placement of a cyst-to-peritoneal shunt if this is unsuccessful The development of minimally invasive endoscopic techniques for use in the brain has made treatment of arachnoid cysts less invasive and has raised some controversy over optimal approaches for different lesions For example, sellar/suprasellar arachnoid cysts in the past have required an open craniotomy for fenestration Today, a transventricular or transnasal endoscopic approach can be employed Numerous retrospective reports on the subject have shown variability in safety and efficacy of each approach.21–24 At the present time, the optimal treatment approach is surgeondependent Chiari Malformations Chiari malformation is defined by a spectrum of brain compression at the level of the posterior fossa and foramen magnum Many types of Chiari malformations have been described by anatomists and clinicians, but two are most commonly seen in the pediatric critical care environment.25–30 Chiari I Malformation Chiari I malformation is defined by the presence of cerebellar tonsillar ectopia with the inferior tip of the tonsils at least mm below the level of the foramen magnum (Fig 59.5) The low-lying • Fig 59.5 Chiari I malformation Sagittal T1-weighted magnetic resonance image shows ectopia of the cerebellar tonsils far below the foramen magnum, consistent with a Chiari I malformation Note the peg-like morphology of the tonsils, which are present more commonly in symptomatic lesions (From Tubbs RS, Hankinson TC, Wellons JC The Chiari malformations and syringohydromyelia In: Ellenbogen RG, Abdulrauf SI, Sekhar LN, eds Principles of Neurological Surgery 3rd ed Philadelphia: Elsevier; 2012:157–168.) 715 tonsils can interfere with the normal flow of CSF across the foramen magnum or cause neurologic compression of the cervicomedullary junction The severity of the malformation dictates the symptomatology, ranging from suboccipital headaches (often induced by coughing or Valsalva maneuver) to symptoms of brainstem compression, including central sleep apnea In particularly severe cases, compression of the brainstem by the Chiari I malformation can cause lower cranial nerve dysfunction These patients may experience dysphagia, dysarthria, or tinnitus.31 Headaches that are not posterior and not elicited by provocative maneuvers are unlikely to be due to the Chiari malformation.25 Some patients with Chiari I malformations may also develop syringomyelia The mechanism by which a syrinx develops is not completely understood, but some have hypothesized that blockage of flow at the obex redirects CSF down the central canal of the spinal cord, resulting in cavitation and cyst formation.32,33 Classically, a cervical syrinx results in a cape-like distribution of pain/ temperature sensory loss first With progressive enlargement, these patients can develop myelopathy, including extremity weakness, sensory changes, gait imbalance, and bowel/bladder incontinence Chiari I malformation is best diagnosed with an MRI of the brain, which will show in detail the anatomy of the cerebellar tonsils and brainstem Patients with round-appearing tonsils close to mm below the foramen magnum are less likely to be symptomatic, whereas those who have more profound tonsillar descent with peg-shaped morphology are more likely to be symptomatic and to benefit from surgery A CSF flow study, such a cine MRI, can also demonstrate obstruction to the normal pulsatile flow of CSF at the foramen magnum.34,35 Our practice is to routinely obtain an MRI of the spine on all patients with a Chiari I malformation to rule out syringomyelia The decision to surgically treat a Chiari I malformation is influenced principally by symptomatology Patients with lifestylelimiting headaches and convincing radiographic findings are usually offered an operation Those who are asymptomatic can be observed safely and treated if they develop symptoms.27,31 Patients with syringomyelia are an exception to this rule; we generally recommend surgical decompression for these patients even in the absence of symptoms to prevent syrinx progression and spinal cord damage The goal of surgery is decompression of the cerebellar tonsils and brainstem A midline suboccipital incision is made to access the cervicomedullary junction The posterior arch of C1 and rim of the foramen magnum are identified and removed In most patients the dura is then opened and a dural patch is sewn in place to expand the posterior fossa dura.36 If the cerebellar tonsils are particularly low lying, bipolar cautery can be used to shrink them This latter maneuver does not typically result in neurologic deficits, although patients may experience a subtle, temporary ataxia Although the postoperative course is generally uneventful, patients are commonly admitted to the ICU overnight to be monitored for neurologic decline or respiratory depression, the latter of which can occur in up to 14% of cases.31 Some controversy exists as to the optimal treatment for Chiari I malformation in the operating room Historically, posterior fossa decompression with duraplasty has been the norm, but ongoing debate has raised the possibility of posterior fossa decompression without duraplasty having similar efficacy when applied in the correct population of patients The optimal population for this less extensive operation (with consequently less risk of CSF leak, meningitis, and wound complications) is not yet clear but is the subject of ongoing trials 716 S E C T I O N V I Pediatric Critical Care: Neurologic Chiari II Malformation By definition, Chiari II malformation associated with myelomeningocele is characterized by low-lying cerebellar tonsils with caudal displacement of the brainstem and fourth ventricle Hydrocephalus is present in most cases because of the associated myelomeningocele Many developmental abnormalities may be associated with a Chiari II malformation, including a small posterior fossa, polymicrogyria, gray matter heterotopias, and hypoplastic brainstem nuclei.25 When symptomatic, neonates and young infants tend to present with signs and symptoms referable to the brainstem and lower cranial nerve dysfunction Neonates may have apneic episodes, which can be due to untreated hydrocephalus or to maldevelopment or compression of the medullary respiratory center Inspiratory stridor and neurogenic dysphagia may also result from brainstem abnormalities.37–39 In general, younger patients with more rapid presentations tend to have worse outcomes In older children, syringomyelia can cause myelopathy and extremity weakness Surgical management of Chiari II malformation is similar to that of Chiari I malformation However, the posterior fossa venous anatomy tends to be atypical in these patients, and our experience is that the expansion duraplasty carries much higher risk in this group As such, open dura is not routinely pursued in these patients Furthermore, decompression in Chiari II patients must be considered in the context of their other potential confounding abnormalities, including the possibility of a tethered spinal cord or malfunctioning CSF diversion Attention to detail and thorough consideration of all diagnostic avenues is critical prior to proceeding with posterior fossa decompression Other Chiari Malformations A subset of patients will present with classic symptoms of Chiari I malformation, syringomyelia, but less than mm of cerebellar tonsillar herniation These patients have been labeled as having Chiari malformation, and frequently have obstruction of CSF flow at the obex when explored surgically.40 A B Chiari 1.5 malformations are those that have characteristics of both Chiari I and II malformations They have no association with neural tube defects but have herniation of both cerebellar tonsils and the cervicomedullary junction through the foramen magnum These patients frequently also have syringomyelia.25 Chiari III malformations account for fewer than 1% of all Chiari malformations.25 They are characterized by occipital or cervical encephaloceles containing tissue from the cerebellum and, in some cases, the brainstem Hydrocephalus is very common, and severe developmental problems are nearly universal Surgical treatment for these patients involves repair of the encephalocele.25 Unlike types I, II, and III, the Chiari IV malformation is not characterized by herniation of brain tissue but is instead an extreme form of cerebellar hypoplasia Maldevelopment of the brainstem is occasionally seen in this condition Surgical decompression is not required Other rarer forms of Chiari malformation have been described but are sufficiently uncommon that their inclusion in this discussion is of limited utility Dandy-Walker Complex The Dandy-Walker complex is a spectrum of posterior fossa malformations characterized by cystic dilation of the fourth ventricle and vermian hypoplasia or aplasia (Fig 59.6) It occurs with a frequency of approximately per 100,000, and between 70% and 90% of patients have hydrocephalus, which is the presenting feature in most.2,41,42 About two-thirds of patients have associated CNS malformations, with agenesis of the corpus callosum being most common Meningoceles, encephaloceles, agyria, polymicrogyria, intrinsic brainstem malformations, and other conditions are also seen.41,43 Some,44–46 but not all,47,48 authors have found a correlation between the presence of these structural abnormalities and intelligence, which is normal in approximately 40% of patients.45 Epilepsy and sensory disturbances may occur as well, which have been consistently shown to correlate with worse cognitive outcome.44 Outside of the CNS, Dandy-Walker malformations are associated with a number of systemic anomalies that can be particularly relevant to the pediatric intensivist For example, cardiac C • Fig 59.6 Dandy-Walker syndrome (A) Prenatal sagittal T2-weighted magnetic resonance image (MRI) shows a large posterior fossa cyst and abnormal cerebellum consistent with Dandy-Walker syndrome. (B) The black arrow indicates a large posterior fossa cyst; the white arrow indicates an abnormal cerebellar vermis (C) Sagittal T2-weighted MRI shows a large posterior fossa cyst with upward displacement of the tentorium (From Choutka O, Mangano FT Dandy-Walker syndrome In: Winn HR, ed Youmans Neurological Surgery Philadelphia: Elsevier; 2011:1906–1910.) CHAPTER 59 Critical Care Considerations for Common Neurosurgical Conditions abnormalities—including tetralogy of Fallot, congenital valve disease, coarctation of the aorta, ventriculoseptal defects, and a patent ductus arteriosus—may cooccur with Dandy-Walker malformations Feeding can be complicated by duodenal atresia, intestinal malrotation, and anorectal malformations Dysplasia of the kidneys and lungs may also occur Finally, DandyWalker malformation is seen in many children with syndromic disorders.43 Neurosurgical management of Dandy-Walker is primarily directed at the treatment of associated hydrocephalus If present, hydrocephalus should be treated by placement of a CSF shunt or ETV.42,49–54 Fenestration of the fourth ventricular cyst has fallen out of favor as a primary treatment because it is associated with unacceptable morbidity and mortality It is generally not performed for patients whose hydrocephalus is adequately treated by a shunt However, several authors have had satisfactory results in patients with recurrent shunt malfunctions.55–57 Encephalocele and Meningocele Encephalocele and meningocele are two related malformations that are characterized by herniation of CNS contents through a skull defect In an encephalocele, the herniated tissue comprises the brain, CSF, and meninges (Fig 59.7); in a meningocele, only CSF and meningeal tissue are involved Encephaloceles occur in approximately to per 10,000 live births and account for 10% to 15% of all neural tube defects.58–60 Primary encephaloceles are developmental in origin, whereas secondary encephaloceles are acquired, most commonly because of trauma, infection, malignancy, or surgery.61 Primary lesions are generally classified based on their location: at the skull base, in the anterior cranial fossa, or along the convexities The relative frequency of these lesions varies with the population studied; occipital encephaloceles (along the calvaria at the occiput) account for 80% of all cases in North America and Western Europe, whereas anterior encephaloceles are more common in Southeast Asia and Africa.61–64 They may occur in isolation Se:3 Im:10 [H] [R] [L] [F] • Fig 59.7 Encephalocele Sagittal T1-weighted magnetic resonance im- age shows an occipital encephalocele with herniation of brain contents through a skull defect and into the sac (From Ghatan S Encephalocele In: Winn HR, ed Youmans Neurological Surgery 6th ed Philadelphia: Elsevier; 2011:1898–1905.) 717 or in conjunction with other anomalies as part of a syndrome, such as in Meckel syndrome or amniotic band syndrome.65–67 Most of these lesions are now diagnosed prenatally with routine ultrasound examinations, prompting delivery of the fetus by cesarean section If not seen on prenatal ultrasound, they are frequently obvious at birth.61 Because clinically significant associated abnormalities are commonly seen throughout the neuraxis, patients with suspected or confirmed encephaloceles should be imaged with an MRI of the brain and spine.61 As many as one-fifth will have an additional neural tube defect, and hydrocephalus is present in 16% to 65% of cases.63,68–70 Neurologic function varies with the location of the lesion and the amount of brain matter in the encephalocele Children with small lesions may have no obvious neurologic findings, whereas more significant cases can present with severe deficits, including brainstem dysfunction not compatible with life Among patients with occipital encephaloceles, approximately 17% will have normal neurologic outcomes.61 Spinal Dysraphism Spinal dysraphism describes a spectrum of related malformations that range in severity from clinically insignificant to life-altering The mildest form, spina bifida occulta, is defined by a congenital absence of all or part of the posterior elements of a lumbar vertebral body Many of these are found incidentally and cause the patient no harm, although some are associated with other abnormalities that predispose the patient to tethered cord syndrome Other forms of spinal dysraphism include meningocele, a cystic dilation of the meninges through a defect in the posterior vertebral elements into the subcutaneous tissues with underlying normal neural structures,71 and lipomyelomeningocele, in which a lipoma attached to the spinal cord herniates through a posterior bony defect Both of these are associated with spinal cord tethering and neurologic dysfunction Spina bifida aperta, or myelomeningocele, lies at the other end of this spectrum Myelomeningocele is the most severe of the malformations of caudal neuropore closure, in which the spinal cord and dura are fused to the skin through a bony defect and the neural placode of the spinal cord is exposed to the outside world There is a resulting loss of function distal to the affected spinal level (Fig 59.8) The malformation is caused by failure of the posterior neuropore to close properly, which, in turn, prevents proper migration of the adjacent ectodermal tissues As a consequence, the involved segment of the spinal cord is exposed as a placode surrounded by fragile arachnoid membranes that tether the neural tissue to the adjacent skin These membranes frequently rupture, leading to loss of CSF and increased risk of infection Chiari malformations are present in most of these children.72 Timely closure of the myelomeningocele is imperative to reduce the risk of infection, which increases after 24 to 36 hours of life because of bacterial colonization.73 To prevent further loss of function, the newborn should be positioned prone to keep pressure off the lesion In addition, the site should be kept moist with saline and covered with saline-soaked nonstick gauze (Telfa) pads.72 We commonly place a “donut” of soaked, sterile sponges around the placode, which ensures that the overlying dressing does not apply pressure to the lesion Surgical techniques used for repair vary from center to center At our institution, the procedure is carried out by a combined team of neurosurgeons and plastic surgeons The neurosurgeon 718 S E C T I O N V I Pediatric Critical Care: Neurologic Central canal Placode Zona epitheliosa CSF Skin Fascia Dura Muscle Vertebral body • Fig 59.8 Axial cross-sectional anatomy of a myelomeningocele Due to failure of primary neurulation, the spinal cord herniates through defects in the vertebrae and soft tissue and is exposed as the placode The placode is surrounded by the zona epitheliosa, a thin layer of epithelial tissue CSF, Cerebral spinal fluid (From Sutton LN, Bauman JA, Macyszyn LJ Spinal dysraphism and tethered spinal cord In: Ellenbogen RG, Abdulrauf SI, Sekhar LN, eds Principles of Neurological Surgery 3rd ed Philadelphia: Elsevier; 2012:89–103.) 2 1 unusually susceptible to the respiratory suppression that these agents cause because of either intrinsically hypoplastic brainstem nuclei or extrinsic compression from associated Chiari malformations As many as 85% of children with myelomeningocele have comorbid hydrocephalus, with more proximal lesions conferring a higher risk of shunt dependence.72,75 Thus, these children should undergo intracranial imaging to evaluate for ventriculomegaly Practice patterns vary among surgeons and centers In general, children with overt hydrocephalus on imaging undergo placement of either a temporary EVD or a permanent shunt at or around the time of their myelomeningocele closure If the neurosurgeon elects not to place an EVD or a shunt, the child must be watched closely for signs and symptoms of untreated hydrocephalus, including a tense fontanelle, splayed sutures, rapidly increasing head circumference, ventricular enlargement on serial ultrasounds, or leakage of CSF from the site of myelomeningocele closure The presence of any of these conditions signals the need for shunt placement Ultimately, outcomes are dependent on the level of the lesion and presence of hydrocephalus Proximal lesions at T12 or L1 cause complete or nearly complete paralysis of the lower limbs, whereas distal lesions at S1 or S2 may cause only mild distal motor symptoms and sphincter dysfunction About half of patients have the ability to ambulate with a brace Seventy percent of patients achieve normal IQ, although that rate is far lower among children who have a shunt infection.73 Recent advances in myelomeningocele management include the advent of intrauterine fetal repair The pathogenesis of ongoing in utero neurologic injury secondary to exposed neural placode has driven the development of clinical trials of fetal repair Participants in the Women in the Management of Myelomeningocele Study were randomized to prenatal repair before 26 weeks’ gestation or standard postnatal repair Outcomes included fetal or neonatal death or the need for CSF shunting by the age of 12 months The trial was halted early due to the efficacy of fetal surgery for reducing the need for shunting and improving motor outcomes at 30 months However, due to increased maternal and fetal perinatal risks, extensive counseling and patient autonomy in deciding on pre- or postnatal repair remains the norm.76 The field of fetal repair remains relatively new and is evolving rapidly; ongoing studies will help guide family counseling going forward Conclusions A B • Fig 59.9 Closure of the myelomeningocele (A) Once the placode is released and the dura is closed, creation of tissue flaps may be required to close larger defects Here, an S-shaped incision surrounds the lesion (B) The tissue flaps are rotated, facilitating a multilayered closure (From Sutton LN, Bauman JA, Macyszyn LJ Spinal dysraphism and tethered spinal cord In: Ellenbogen RG, Abdulrauf SI, Sekhar LN, eds Principles of Neurological Surgery 3rd ed Philadelphia: Elsevier; 2012:89–103.) releases the placode, reapproximates the spinal cord and closes the dura in a watertight fashion to prevent leakage of CSF The plastic surgery team then mobilizes adjacent soft-tissue flaps to perform a layered closure (Fig 59.9).74 As in the preoperative period, the patient is kept prone postoperatively to prevent pressure on the wound Use of narcotics should be limited; many patients are Congenital anomalies of the brain create unique challenges for pediatric critical care providers General principles apply, but an understanding of the basic embryology and physiology of each developmental malformation is essential in providing the appropriate care for these often complex patients Key References Adzick NS, Thom EA, Spong CY, et al A randomized trial of prenatal versus postnatal repair of myelomeningocele N Engl J Med 2011; 364(11):993-1004 Al-Holou WN, Yew AY, Boomsaad ZE, Garton HJ, Muraszko KM, Maher CO Prevalence and natural history of arachnoid cysts in children J Neurosurg Pediatr 2010;5(6):578-585 Garton HJ The Dandy-Walker complex and arachnoid cysts In: Albright AL, Pollack IF, Adelson PD, eds Principles and Practice of Pediatric Neurosurgery 3rd ed New York, NY: Thieme; 2015:145-161 CHAPTER 59 Critical Care Considerations for Common Neurosurgical Conditions Greenberg MS Developmental anomalies In: Greenberg MS, ed Handbook of Neurosurgery 7th ed New York, NY: Thieme; 2010: 222-261 Jimenez DF, Barone CM Encephaloceles, meningoceles and dermal sinuses In: Albright AL, Pollack, IF, Adelson, PD, eds Principles and Practice of Pediatric Neurosurgery 3rd ed New York, NY: Thieme; 2015:205-229 Kahle KT, Kulkarni AV, Limbrick Jr DD, Warf BC Hydrocephalus in children Lancet 2016;387(10020):788-799 Kestle JR, Riva-Cambrin J, Wellons JC III, et al A standardized protocol to reduce cerebrospinal fluid shunt infection: the Hydrocephalus Clinical Research Network Quality Improvement Initiative J Neurosurg Pediatr 2011;8(1):22-29 Kulkarni AV, Drake JM, Kestle JR, et al Predicting who will benefit from endoscopic third ventriculostomy compared with shunt insertion in childhood hydrocephalus using the ETV Success Score J Neurosurg Pediatr 2010;6(4):310-315 719 Kulkarni AV, Riva-Cambrin J, Butler J, et al Outcomes of CSF shunting in children: comparison of Hydrocephalus Clinical Research Network cohort with historical controls: clinical article J Neurosurg Pediatr 2013;12(4):334-338 Kulkarni AV, Riva-Cambrin J, Rozzelle CJ, et al Endoscopic third ventriculostomy and choroid plexus cauterization in infant hydrocephalus: a prospective study by the Hydrocephalus Clinical Research Network J Neurosurg Pediatr 2018;21(3):214-223 Strahle J, Muraszko, K Spinal meningoceles In: Albright AL, Pollack IF, Adelson PD, eds Principles and Practice of Pediatric Neurosurgery 3rd ed New York, NY: Thieme; 2015:286-293 Tubbs RS, Griessenauer CJ, Oakes WJ Chiari malformations In: Albright AL, Pollack, IF, Adelson, PD, eds Principles and Practice of Pediatric Neurosurgery 3rd ed New York, NY: Thieme; 2015: 192-204 The full reference list for this chapter is available at ExpertConsult.com ... occasionally seen in this condition Surgical decompression is not required Other rarer forms of Chiari malformation have been described but are sufficiently uncommon that their inclusion in this discussion... Principles and Practice of Pediatric Neurosurgery 3rd ed New York, NY: Thieme; 2015: 192-204 The full reference list for this chapter is available at ExpertConsult.com ... and 90% of patients have hydrocephalus, which is the presenting feature in most.2,41,42 About two-thirds of patients have associated CNS malformations, with agenesis of the corpus callosum being