Duodenal somatostatinoma: a case report and review of 31 cases with special reference to the relationship between tumor size and metastasis.

Somatostatinomas are rare functioning neoplasms usually arising in the pancreas and duodenum. We report a case of somatostatinoma in a 42-year-old male with neither neurofibromatosis nor somatostatinoma syndrome. A large tumor in the descending duodenum had given rise to multiple lymph node metastases. An additional 31 duodenal somatostatinoma cases were also reviewed. Most originated in the descending part of the duodenum, with the ampulla and peri-ampullary area as the most common sites (60%). Frequent manifestations were abdominal pain (25%), jaundice (25%), or cholelithiasis (19%), the latter two reflecting obstruction of the bile duct by tumors. Only two cases showed a possible somatostatinoma syndrome (6%). The tumors with metastases, lymph nodes (10) and liver (2), were significantly larger than average than those without (2.91 +/- 1.49 cm vs 1.36 +/- 0.71 cm, P < 0.05). With a cut-off point of 2.0 cm, diagnostic accuracy for metastasis was 77.78% with 87.50% specificity and 63.64% sensitivity. The smallest tumor with metastases was 0.8 cm and the largest without metastases was 3.0 cm. These results indicate that duodenal somatostatinomas are malignant by nature and the risk of metastasis significantly increases with tumors larger than 2.0 cm.