Encephaloceles

An encephalocele is a protrusion of brain and meninges beyond the confines of the skull. Most are covered by skin although this is not always the case. They are usually divided into anterior and posterior groups. The anterior group is further subdivided into those encephaloceles that extend between the frontal bone and other facial bones, and those that can extend inferiorly through the skull base. This latter group may not have any obvious visible anomaly, and only come to attention when

other neurological deficits are detected. The cause of encephaloceles is believed to arise from arrested closure of mesodermal tissue, with early protrusion of brain neural tissue through the defect.

While closed lesions may be observed, open lesions and lesions with symptomatic mass affect (e.g., airway obstruction) may need early closure. Repair of an en-cephalocele is similar to a myelomeningocele repair. The external sac is opened and nonfunctional extracranial tissue is excised. The dura is closed or a pericranial graft is used to form a watertight closure. Long-term outcome is usually dependent upon the amount of nervous tissue within the encephalocele and the presence of hydro-cephalus. Small encephalocele are compatibles with normal cognitive function.

Congenital Tumors

Congenital tumors are extremely rare, representing 2% to 5% of all childhood brain tumors. They are detected either antenatally during a screening ultrasound or postnatally in the setting of hydrocephalus. The pathology of these tumors is diverse, but most are primitive neuroectodermal tumors (PNET), teratomas, astrocy-tomas, or choroid plexus neoplasms.

Vascular Malformations

Cerebral vascular malformations are divided into four types: arteriovenous malformations (AVM), cavernous angiomas, capillary telangiectasias and developmental venous anomalies. These malformations are discussed in greater detail in Chapter 12. AVMs are congenital malformations formed in the sixth to eleventh week of gestation and are located within the brain parenchyma. The physiological abnormality is a low-resistance shunt directing blood from the high-pressure arterial tree to the low-pressure venous system. These malformations can present in a variety of ways in the neonatal period, including macrocephaly secondary to hydrocephalus, spontaneous hemorrhage, or high-output cardiac failure. Hydrocephalus may occur secondary to intraventricular hemorrhage or from venous hypertension.

Vein of Galen malformations (VOGM) are a rare type of arteriovenous malformation, that are usually diagnosed during the first year of life. An arteriovenous shunt directs arterial blood directly into the vein of Galen, which can become enormously dilated. If the shunt is large, high-output cardiac failure can develop and is the most common presenting sign in the neonatal age group.

Suggested Readings

1. Frim DM, Madsen JR. Neurosurgery of the neonate. Neurosurg Clin N Am 1998; 9.

2. Madsen JR, Frim DM. Neurosurgery of the newborn. In: Avery GB, Fletcher M, MacDonald MG, eds. Neonatology: Pathophysiology and Management of the Newborn. 5th ed. Lippincott, 1999

3. Resch B, Gedermann A, Maurer U et al. Neurodevelopmental outcome of hydrocephalus following intra-/periventricular hemorrhage in preterm infants: short-and long-term results. Childs Nerv Syst 1996; 12:27-33.

Chapter 6

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