Radionuclide shunt patency study for evaluation of suspected ventriculoperitoneal shunt malfunction in adults with normal pressure hydrocephalus

OBJECTIVE: Shunt patency studies are performed to determine whether shunt revision surgery is needed in malfunctioned ventriculoperitoneal shunt. The aim of our study was to develop a simple diagnostic algorithm in the diagnostic workup and identify factors associated with improvement after revision surgery. METHODS: A retrospective review of patients with confirmed shunt obstruction who underwent a revision surgery and were followed for 6 to 12 months was performed. A simpler algorithm to identify shunt obstruction was created and compared with the 4-variable algorithm. RESULTS: Of the 63 patients in whom shunt obstruction was suspected, 39 were diagnosed with complete or partial obstruction. Thirty-seven patients underwent shunt revision surgery that included removal of shunt (n = 2), conversion to a ventriculoatrial shunt (n = 8), and relocation of the distal end of the catheter into a different part of the peritoneal cavity (n = 27). Improvements were seen in 63.3% (n = 19) of patients evaluated at 6 months and 63.6% (n = 14) of patients evaluated at 12 months. The positive predictive value of the study was 80%. A simpler 1-variable algorithm using T1/2 (half-time) could correctly classify 86.9% of patients with shunt obstruction, compared with a 4-variable algorithm that correctly classified 80% of patients. CONCLUSION: Shunt patency studies are very useful for evaluation of shunt patency. Their results can be interpreted using a single-variable (T1/2) algorithm. Patients most likely to respond to a revision surgery are those who had a good response to original placement of a ventriculoperitoneal shunt.