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Key Points

  • Hydrocephalus is usually due to obstruction of CSF flow, either within (noncommunicating hydrocephalus) or outside (communicating hydrocephalus) the ventricles.

  • Ventriculomegaly simply refers to enlargement of intracranial ventricles. It can be associated with hydrocephalus or abnormal brain development.

  • Ventriculomegaly is commonly defined as a measurement of 10 mm or greater in the posterior horns of the lateral ventricles noted on an axial brain scan, irrespective of gestational age.

  • Approximately 40% of cases of ventriculomegaly have associated CNS or extra-CNS abnormalities, and 12% have an abnormal karyotype.

  • Underlying causes include aqueductal stenosis, meningomyelocele, intrauterine infection (CMV, toxoplasmosis, syphilis), agenesis of corpus callosum, X-linked hydrocephalus syndromes, intracranial hemorrhage, Dandy–Walker malformation, and intracranial tumors.

  • L1CAM gene mutations account for up to 25% of male cases of isolated congenital hydrocephalus.

  • Recurrence risk, in the absence of a positive family history, or a known L1CAM mutation, is approximately 4%.


Hydrocephalus is a pathologic increase in intracranial cerebrospinal fluid (CSF) volume, whether intraparenchymal or extraparenchymal, independent of hydrostatic or barometric pressure (Raimondi, 1994). CSF is formed within the ventricular system—50% from the choroid plexus and 50% from the cerebral capillaries. The circulation of CSF is unidirectional (Vintzileos et al., 1983). It flows from the lateral ventricles through the foramen of Monro into the third ventricle. It then flows from the third ventricle to the aqueduct of Sylvius through the fourth ventricle into the spinal subarachnoid space (foramen of Magendie) or to the basal cisterns (foramen of Luschka) over the cerebral hemispheres. CSF is reabsorbed by arachnoid villi in venous sinuses. The flow of CSF is partially derived by arterial pulsations of the choroid plexus (Vintzileos et al., 1983).

Hydrocephalus may result from either fluid production that exceeds absorption or primary atrophy of the cerebral parenchyma. Most cases are due to mechanical obstruction to the flow of CSF at some level (DeLange, 1977). The site of obstruction may be inside the ventricular system (noncommunicating or internal hydrocephalus) or outside the ventricles (communicating or external hydrocephalus). Aqueductal stenosis comprises one-third of the cases of hydrocephalus in postnatal series; it is less common in prenatal studies. The aqueduct of Sylvius is the narrowest portion of the spaces through which the CSF flows, and aqueductal stenosis can be diagnosed following the finding of dilation of both lateral, and the third, ventricles (Raimondi, 1994; Davis, 2003).

Ventriculomegaly is a descriptive term of a pathologic process that has many causes. It may occur due to obstruction of CSF flow, or as a consequence of maldevelopment of the ventricle in anomalies such as agenesis of the corpus callosum (colpocephaly) or as an ex vacuo (destructive) phenomenon secondary to cerebral atrophy (Cardoza et al., 1988a). Ventriculomegaly is an indicator of underlying central nervous system (CNS) anomalies. It may also be the first sign of associated ...

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