The diagonal ventricular dimension: a method for predicting shunt malfunction on the basis of changes in ventricular size.

Abstract

Serial computed tomographic and magnetic resonance imaging studies are critical in the evaluation of patients who present with symptoms and signs of recurrent hydrocephalus or possible ventricular shunt malfunction. Subtle changes in ventricular volume or complex variations in ventricular anatomy often make subjective assessment of changes in ventricular size difficult, and no previously described method relates these changes to intracranial pressure or shunt system function. The purpose of this study was to develop an objective, reproducible, simple linear method of detecting changes in ventricular size that provides an accurate reflection of shunt function on the basis of serial imaging studies. We developed a simple, linear estimate of ventricular volume--the diagonal ventricular dimension--to objectively assess changes in ventricular size on serial computed tomographic scans and magnetic resonance imaging scans. Serial imaging studies for 14 patients ages 1.6 to 71 years who underwent evaluation for shunt malfunction were used in this study. The sensitivity and specificity of this method in predicting shunt malfunction was compared with other well-established linear estimates of ventricular size as well as with a radiologist's interpretation of the same studies. The "gold standard" for measuring the status of ventricular shunt system function in this study was the measurement of intracranial pressure via shunt tap or surgical exploration results. The sensitivity (100%) and specificity (100%) of the diagonal ventricular dimension in detecting changes in ventricular size consistent with shunt malfunction was superior to that of any other linear estimate and to a radiologist's interpretation of the same films. The diagonal ventricular dimension provides an objective, simple linear method of assessing changes in ventricular size that correlates well with shunt system function in the context of a collaborative examination.