Localization of small islet-cell tumors. Preoperative and intraoperative ultrasound, computed tomography, arteriography, digital subtraction angiography, and pancreatic venous sampling.

A total of 42 islet-cell tumors were examined between 1972 and 1984. Problems of localization were only encountered in 31 tumors less than 2 cm in diameter. Of 31 small tumors, 27 were correctly localized using a combined diagnostic approach: ultrasound was successful in 12/20 tumors, CT in 9/21, angiography in 20/31, intraarterial digital subtraction angiography in 1/2, and pancreatic venous sampling in 13/16. The smallest tumor found by ultrasound and CT was 7 mm in diameter. Intraoperative ultrasound demonstrated all 9 insulinomas examined. Currently, the most useful techniques for localizing small islet-cell tumors are ultrasound, CT, and angiography. CT is particularly useful for tumor staging. Improvement of non-invasive diagnostic techniques will obviate the need for transhepatic blood sampling.