A critical analysis of 'normal' radionucleotide shuntograms in patients subsequently requiring surgery

Background: Shuntograms are performed when patients present with symptoms suggestive of, but inconclusive for, shunt malfunction, without confirmatory radiological evidence. Methods: Shuntograms over the past 3.5 years were reviewed. Patient records were reviewed for revision in proximity to a negative (normal) study. Results: One hundred and fifteen out of 149 tests were negative. Thirty-four surgeries (in 31 patients) occurred subsequent to a negative shuntogram. In 18 out of 34 revisions the shunt was functional: 13 surgeries were for overdrainage, 4 were for unrelated reasons with shunt function confirmed incidentally and 1 was an exploration for cognitive deterioration. In 16 cases (13 patients) the shunt was not functional: 12 had proximal catheter occlusion in which, on subsequent review, there was no ventricular reflux present and the remaining had distal malfunctions. Conclusions: The false negative rate for shuntograms was 16 out of 115 (14%) with proximal occlusion most common. This estimate of the predictive value of a normal flow study may influence the decision to revise a shunt.