Anatomopathology of non-tumoral aqueductal stenosis.

The aqueduct (A) is the most common site of intraventricular blockade of CSF flow. There are multiple causes of its obstruction which can be classified as congenital or acquired, but their morphological differentiation is often impossible, since in both human and experimentally induced obstructions of the A. various histological changes (narrowing, forking, gliosis) may occur. Occlusion of the A. results in internal hydrocephalus that may arise before or after birth, but in some forms of communicating hydrocephalus stenosis of the A. occurs as a secondary phenomenon due to compression of midbrain or other functional CSF block. The major types of non-tumoral stenosis of the A. include: Hereditary varieties occurring as X-linked recessive trait often as part of a malformation syndrome (Edwards et al., 1961) and rarely without sex-linkage. A. stenosis may be a cause or a consequence of hereditary hydrocephalus. Congenital obstruction of A. co-existing with other CNS malformations, e.g. with spina bifida and the Arnold-Chiari malformation often associated with hydrocephalus, or with hydranencephaly where A. stenosis is primary or secondary in origin. Gliotic obstruction as a common part of widespread ependymitis or sequelae of pre-, neonatal and infantile meningitis, toxoplasmosis or viral infections, less often due to organized intraventricular hemorrhage. Rare septum formation at the caudal end of the A. as minimal form of stenosis. Rare compression of A. by vascular malformations, retrocerebellar cysts (Dandy-Walker syndrome), etc. Experimentally induced obstructions of the A. due to nutritional (vitamin deficiencies), infectious (intrauterina, postnatal infections with rheo-, paramyxo-, arboviruses, etc.) causing non-inflammatory obstructions, and hereditary factors (congenital A. stenosis in mouse mutants) often show parallels to human disease. Their value in etiologic research on non-tumoral aqueductal stenosis is discussed.