Specific Imaging Findings

Neuroimaging of aqueductal stenosis (AS) is characterized by a variable, often severe dilation of the supratentorial ventricles and a normal fourth ventricle. Enlargement of the frontal and temporal horns is commensurate; this is an important differential sign from ex-vacuo ventriculomegaly, especially in newborns in whom, owing to compensatory macrocrania, the subarachnoid spaces may remain prominent or even frankly enlarged even with hydrocephalus. The site of stenosis or complete obstruction (either proximal or distal) is best depicted with high-resolution 3D heavily T2WI. Absence of normal aqueductal flow-void on T2WI can be confirmed with flow-sensitive MR techniques (phase-contrast). Periventricular edema is not usually prominent in infants, but becomes more frequent once the cranial sutures have closed, and indicates uncompensated hydrocephalus requiring surgical attention. Septum pellucidum may become fenestrated or even undiscernible with severe long-standing hydrocephalus. Following successful endoscopic third ventriculostomy, T2-weighted and flow-sensitive images will show turbulent CSF flow through the floor of the third ventricle.

Pertinent Clinical Information

Clinical manifestations of AS vary depending on patient age and duration of raised intracranial pressure. Patients with prenatal diagnosis of ventriculomegaly are seen immediately after birth before significant symptoms ensue. During the first two years, presentation is with abnormally accelerated head growth: disproportionately large forehead, wide sutures, tense fontanel, and engorged scalp veins. At this age, neurological signs are insidious including difficulty feeding and laryngeal stridor. Downward gaze deviation (“setting-sun sign”) occurs in the most severe cases.