Radioiodinated Serum Albumin (RISA) Cisternography in the Diagnosis of Incisural Block and Occult Hydrocephalus

Abstract
The usefulness of radioiodinated serum albumin (RISA) cisternography as a supplemental diagnostic procedure in patients with incisural block is discussed. After lumbar intrathecal injection of RISA, the radioactivity will appear in the basal cisterns on a 3-hour scan. At 24 hr., a scan will show the gradual migration of the radioactivity to the subarachnoid spaces of the convexity of cerebral hemispheres through the tentorial incisura. If there is retention of radioactivity in the basal cisterns and no radioactivity can be detected over the convexity of the brain on 24- and 48-hr. scans, incisural block as the cause of hydrocephalus is established.