Intraventricular "RISA" as a diagnostic aid in pre- and postoperative hydrocephalus.

Abstract

A technique is described for evaluating the presence of hydrocephalus by measurement of the decrease in RISA concentration in ventricular cerebrospinal fluid from the 1-hr level at 4 hr and 24 hr following injection of a 5-mC test dose. The technique was found satisfactory in classifying normal. active hydrocephalic, and arrested hydrocephalic patients. Concentration of radioactivity in blood was found to be too low to be generally useful. In patients with ventriculoatrial shunts, radioactivity in blood frequently showed a sudden surge indicating a functioning shunt. The variable finding depended apparently on time of sampling and rate of flow in the shunt. The 1-hr concentration of RISA in ventricuiar cerebrospinal fluid was an unreliable index of activity of hydrocephalus. Concentrations of RISA in lumbar cerebrospinal fluid were an unreliable index of concentration of RISA in ventricular cerebrospinal fluid. A model is proposed for the dynamic characteristics of the cerebrospinal fluid-protein system. It is proposed that the most common basic defect in hydrocephalus is a critical reduction in area of available subarachnoid space where interfaces allow cerebrospinal fluid-brain mechanisms of transfer to take place. (H.H.D.)