Topographic diagnosis and surgical treatment of insulinoma

Controversy continues to reign with regard to the need for preoperative localization of insulinomas and to which are the most sensitive and accurate diagnostic imaging modalities. Our aim was to determine the role of diagnostic procedures and suggest which of them are really useful.

Over a 12-year period 34 patients underwent several preoperative diagnostic procedures to localize the insulinoma: ultrasonography (US) in 20 cases, computed tomography (CT) in 26, magnetic resonance imaging (MRI) in 28, selective angiography in 8, arterial stimulation venous sampling (ASVS) in 23 and Octreoscan in 26. All patients underwent surgical palpation and in 32 cases intraoperative ultrasonography (IOUS) was performed. Twenty-six cases underwent enucleation, six had distal pancreatic resections and two patients had only exploratory laparotomy with liver biopsies. We compared the findings of the diagnostic procedures and analyzed the surgical treatment chosen according to the pancreatic site of the tumor.

In 32 (94.1%) of the 34 patients with clinically suspected pancreatic insulinoma the tumor was found at surgery. Preoperative US achieved 5.2% sensitivity, CT 29.1%, selective angiography 28.5% and MRI 76.9%. ASVS achieved 91.3% sensitivity and diagnostic accuracy whereas Octreoscan achieved only 65.3% diagnostic accuracy. Surgical palpation performed before IOUS identified the tumors in 30/34 patients: in the other four cases, one was a false-positive result (a cyst in the pancreatic head), two were true negatives and one was a false negative. Surgical palpation therefore yielded 88.2% diagnostic accuracy. IOUS was performed in 32 cases and localized the tumors in 29/32 cases (sensitivity: 96.6%) with one false-negative result (diagnostic accuracy: 96.8%). The operative mortality was 2.9% and the morbidity 24.6% (30.7% in patients treated by tumor enucleation).

No single diagnostic imaging modality is reliable for localizing insulinoma. We therefore suggest combined MRI, ASVS and IOUS. ASVS provides particularly useful information for planning manual palpation and intraoperative ultrasonography.