Anterior, posterior, and lateral head and neck images are obtained 48 hours after the intrathecal administration of indium 111-DTPA (cerebrospinal fluid [CSF] cisternography). Abnormal extracranial nasal activity is noted bilaterally (circle), most intensely in the left upper portion (arrow).

Differential Diagnosis

•  Anterior CSF leak: Extracranial passage of CSF is abnormal and makes this the correct diagnosis.

•  Arachnoid cyst: This can also appear as an abnormally increased collection of CSF if it communicates with the remainder of the CSF space. However, it should appear intracranial.

•  Normal pressure hydrocephalus: Although this is the other common indication for radionuclide cisternography, no reflux into the third or lateral ventricles is present.