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EVALUATION OF CAUSES OF FALSE POSITIVE Tc‐99m-IDA SCINTIGRAPHY IN BILIARY ATRESIA

Fourty-three patients were evaluated by Tc-99m-IDA scintigraphy for possible biliary atresia. Thirty-four earlier scans were done with Tc-99m-PIPIDA and nine scans were done with Tc-99m-DISIDA. There were sixteen true positives, defined as no gastrointestinal activity by twenty-four hours after pre-treatment with phenobarbital 5 mg/kg/day for three days. There were seventeen true negatives, ten false positives and no false negatives. Causes for false positives included two studies done without phenobarbital, five neonatal hepatitis and three cases of cholestasis associated with septo-optic dysplasia. If the two cases done without phenobarbital are excluded, sensitivity is 100% and specificity is 68%. Recognizing septo-optic dysplasia and cholestasis clinically further increases specificity to 77%. In the remaining false positives with neonatal hepatitis, four of five had poor hepatic uptake however two of sixteen biliary atresia cases also had poor hepatic uptake. If reduced hepatic activity is used as a criterion against biliary atresia, specificity increases to 94% but sensitivitiy decreases to 88%. Septo-optic dysplasia is an unusual syndrome characterized by absent septum pellucidum, hypoplasia of one or both optic nerves, and hypothalamic pituitary dysfunction. False positive biliary atresia interpretation can be reduced by careful physical examination and recognition of this entity. Poor hepatic uptake in cases with no twenty-four hour gastrointestinal activity can be helpful in ruling against biliary atresia.