C. Selected congenital malformations associated with hydrocephalus

1. Arnold-Chiari malformation. The term "Chiari malformation" encompasses a complex of abnormalities of the brainstem and cerebellum. Four types have been described. Type II, called the Arnold-Chiari malformation, is the most common and is almost always associated with polymicrogyria, meningomyelocele, and hydrocephalus. There is a probable pattern of multifactorial inheritance. The Arnold-Chiari malformation is characterized by:

a) tongues of gliotic cerebellar tissues extending along medulla and cervical spinal cord

b) elongation of medulla, pons and 4th ventricle, with kinking of medulla.

c) "beak"-shaped malformation of colliculi

d) acqueductal stenosis

e) small posterior fossa, large foramen magnum

Example of features of Arnold-Chiari malformation

 

2. The Dandy-Walker malformation has a high recurrence risk (1.5%) reported in first cousin matings. It is associated, in some cases, with congenital heart. Pathological characteristics include:

a) cystic dilatation of 4th ventricle, with wall of cyst composed of ependyma and leptomeninges

b) lateral displacement of cerebellar hemispheres by 4th ventricle

c) malformation of vermis (anterior vermis displaced rostrally, inferior vermis reduced to abnormal white matter on medial surfaces of hemispheres.

d) increased volume of posterior fossa, with upward displacement of lateral venous sinuses.

e) obstruction of foramina of Luschka and Magendie

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