Radionuclide shunt patency study for suspected ventriculoatrial shunt malfunction

OBJECTIVE: Radionuclide shunt studies have been used for decades to evaluate intracranial shunt patency (SP); however, the methodology is neither standardized nor well validated. The purpose of this study was to determine the clinical utility of radionuclide ventriculoatrial (VA) SP study for diagnosis of suspected shunt malfunction. METHODS: A retrospective review was undertaken of all patients who had a VA radionuclide SP study between 2001 and 2009. All had a 20-minute gamma camera acquisition (1 min/frame) immediately following injection of Tc DTPA into the shunt reservoir. Time-activity curves were generated and a half-time (T1/2) of emptying quantified. The results were correlated with the final clinical diagnoses. RESULTS: Forty-nine studies in 40 adult patients with a minimum of 6 months' follow-up were analyzed. Thirteen shunt studies had a T1/2 of 3.9 to 8.0 minutes, had final diagnosis of normal functioning shunt, and did not need revision surgery for a mean follow-up of 15.1 months. Fourteen patient studies had a T1/2 of less than 3.9 minutes; 13 had final diagnosis of overdraining shunts, and 1 required revision surgery. Twenty-two had a T1/2 longer than 8 minutes: 13 had final diagnosis of shunt obstruction, 4 had overdrainage, and 5 had underdrainage. CONCLUSIONS: The radionuclide SP study is valuable for evaluation of VA SP. Results can be interpreted using a single variable (T1/2). T1/2 of 3.9 to 8 minutes indicates a patent shunt; T1/2 less than 3.9 minutes is consistent with overdrainage. T1/2 of >8 requires further evaluation to differentiate between obstruction and overdrainage/underdrainage.