Anterior and lateral images from a radionuclide cisternogram obtained with indium 111 DTPA reveal incomplete migration of radiotracer over the convexities by 24 hours. Lateral ventricular reflux is also noted (arrows). By 48 hours, further but incomplete migration is noted, and persistent reflux is seen in the lateral ventricles.

Differential Diagnosis

•  Obstructive communicating hydrocephalus: Delayed flow over the convexities with reflux into the ventricles is indicative of this diagnosis. Normal-pressure hydrocephalus (NPH) is a subtype of obstructive communicating hydrocephalus.

•  Cerebrospinal fluid (CSF) leak: Although this is another common indication for radionuclide cisternography, there is no evidence of extracranial passage of radiotracer.

•  Normal variant: Persistent reflux of radiotracer into the ventricles is never normal.