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Surgical management, pre-operative tumor localization and histopathology of 80 patients operated for insulinoma.

INTRODUCTION
Diagnosis and pathological classifications is challenging in insulinomas.


AIM
To characterize insulinoma patients with regard to localization of tumors, surgery outcomes and histopathology.


METHODS
All patients with surgical resected sporadic insulinoma were included.


RESULTS
Eighty patients were included. Seven had a malignant tumor. 312 diagnostic examinations were performed: Endoscopic ultrasonography (EUS, n=59, sensitivity 70%), magnetic resonance imaging (n=33, sensitivity 58%), computed tomography (CT, n=55, sensitivity 47%), transabdominal US (n=45, sensitivity 40%), somatostatin receptor imaging (n=17, sensitivity 29%), 18F-FDG positron emission tomography/CT (n=1, negative), percutaneous transhepatic venous sampling (n=10, sensitivity 90%), arterial stimulation venous sampling (n=20, sensitivity 65%) and intra-operative US (n=72, sensitivity 89%). Fourteen tumors could not be visualized despite the use of numerous different imaging modalities. Invasive methods were used in 7 of these 14 patients and localized the tumor in all cases.Median tumor size was 15 mm (range 7-80 mm). All tumors tested were positive for chromogranin A and synaptophysin. Tumors with malignant vs. benign behavior showed less staining for insulin (3/7 vs. 66/73, p=0.015) and for proinsulin (3/6 vs. 58/59, p<0.001). Staining for glucagon was seen in 2/6 malignant tumors vs. none in benign tumors (p<0.001). Forty-three insulinomas stained negative for SSTR-2a. Amyloid, somatostatin, pancreatic polypeptide and CD117 staining were negative in the vast majority of tumors.


CONCLUSION
Localization of insulinomas require a substantial number of different diagnostic procedures. The majority of tumors can be localized by conventional imaging including EUS. In case of non-visible tumors, invasive methods may be a useful diagnostic tool. Malignant tumors showed reduced staining for insulin and pro-insulin and increased staining for glucagon.