DIFFERING SCINTIGRAPHIC PATTERNS OF LUMBOPERITONEAL SHUNT DYSFUNCTION IN PATIENTS WITH NORMAL-PRESSURE HYDROCEPHALUS AND PSEUDOTUMOR CEREBRI

The scintigraphic patterns of dysfunctioning lumboperitoneal shunts (LPS) may vary with the underlying disease. The authors reviewed 22 LPS studies performed on 15 patients during the past 2 years and correlated the findings with the patency status of the shunt as determined by brain CT/MRI and surgical revision. Most of the patients also had cerebrospinal fluid (CSF) pressure monitoring. Fifteen studies were performed in patients with LPS for the treatment of normal pressure hydrocephalus (NPH) and 7 were performed in patients with LPS for pseudotumor cerebri (PTC). After intrathecal administration of 0.5-1 mCi of In-111 DTPA, sequential 1 minute images of the abdomen were obtained for 20 minutes. Static images of the abdomen were then obtained at 30 minutes and 1, 2, 4, and 24 hours with imaging of the head at 4 and 24 hours. All NPH patients with partial obstruction had tracer activity in the peritoneal cavity with little or no shunt tubing visualization. However, all had marked penetration of the tracer into the lateral ventricles. Pseudotumor cerebri patients with partial obstruction also showed tracer entry into the peritoneal cavity. Shunt tubing and tracer extravasation into the needle tract, at the site of lumbar puncture was seen only in patients of PTC, probably because of high intracranial pressure. Although the tracer flowed quickly into the basal cistern in all patients with PTC, it entered the lateral ventricles. Complete shunt obstruction was characterized by nonvisualization of activity in the peritoneal cavity and flow of the tracer into the basal cistern within 1 hour after injection. Head imaging patterns in completely obstructed shunts were similar to those seen with partial obstruction. In summary, the diagnosis of the patients of totally obstructed shunts is relatively simple, but diagnosis of partial LPS obstruction may be difficult. Peritoneal activity was seen in all shunts with partial obstruction and does not imply normal patency. Rapid and marked accumulation of the tracer in the basal cistern or into the ventricles should suggest malfunction. Also, the scintigraphic pattern of shunt dysfunction in patients with NPH differs from that seen in patients with PTC.