Imaging description

Hydrocephalus in adults is usually non-communicating secondary to obstruction of cerebrospinal fluid (CSF) pathways by tumor, mass effect, infection/inflammation, or blood by-products. Normal-pressure hydrocephalus (NPH) is a communicating form of hydrocephalus and usually seen in the elderly. Hydrocephalus secondary to aqueductal stenosis (AS) is a well-known entity in pediatric populations but it is not widely recognized in adults despite the fact that primary AS is responsible from 10% of the adult hydrocephalus cases [1]. The majority of adult-onset AS cases remain idiopathic, while X-linked recessive inheritance has been reported in some cases. It is not clear whether AS in adults exists since birth but symptoms are delayed, or if it develops later in life, although some evidence suggests that patients exhibit ventriculomegaly long before they develop symptoms.

Typically, a diagnosis of communicating hydrocephalus is suggested in an adult with ventriculomegaly and no obstructing lesion demonstrated on MRI. In this setting, standard MRI sequences show enlargement of the third and lateral ventricles with relative normal size of the fourth ventricle. Addition of a high-resolution T2-weighted sequence, such as CISS, FIESTA, or DRIVE, to standard imaging protocols, however, may allow positive demonstration of aqueductal webs and establish the diagnosis of non-communicating hydrocephalus (Fig. 47.1). Phase contrast CSF flow studies may demonstrate lack of flow through the cerebral aqueduct, but sensitivity and specificity of this technique are limited.