Islet Cell Tumor of the Pancreas

George M Wu, MD
Gregory T Sica, MD

April 26, 1996

Presentation

UGI images courtesy of Harvard Community Health Plan, Boston.

Imaging Findings

An upper gastrointestinal (UGI) examination demonstrates shelf-like deformity (arrow) of the medial wall at the junction of the first and second portions of the duodenum. A double contour (arrow) is visible on a spot view of this area. The frontal view of the abdomen demonstrates widening of the duodenal C-sweep and Frostberg's inverted three sign (arrow).

Abdominal computed tomographs (CT) obtained after administration of oral and intravenous contrast media show a 4 cm homogeneously enhancing mass (arrow) in the head of the pancreas. No calcifications are visible within this mass. There is no evidence of pancreatic or biliary ductal dilatation. The duodenal wall is not clearly distinct from the mass. No vascular encasement or invasion, lymphadenopathy, or liver metastasis are apparent.

Differential Diagnosis

In contrast, pancreatic adenocarcinoma usually is hypovascular and has a more heterogeneous enhancement pattern. The patient's age and gender and the location of the mass might support a diagnosis of microcystic adenoma. However, central calcifications are seen in up to 40% of microcystic adenomas on CT and, sometimes, a central scar is also present. In addition, while microcystic adenomas do enhance, the enhancement of the current case is uniform and no cysts are discernible. Solid papillary epithelial neoplasm, an uncommon tumor, is found in younger women with a mean age of 24 and occurs more frequently in the tail of the pancreas. The typical appearance on CT is a mixed attenuation mass with areas of hemorrhage and necrosis. After the administration of intravenous contrast, the neoplasm tends to enhance heterogeneously and less densely than an islet cell tumor.

In view of the patient's age, metastasis might also be a consideration (although it is rare). Direct extension from a contiguous organ is more likely than hematogenous spread. More common hematogenous metastases include melanoma, breast carcinoma and bronchogenic carcinoma. The vascularity of a metastasis depends on the primary malignancy; however, a metastasis often has a degree of central necrosis, which is not present in the current case.

Diagnosis

Discussion

Gastrinoma is one of six types of pancreatic islet cell tumors. The others are insulinoma, glucagonoma, VIPoma, somatostatinoma and nonfunctioning islet cell tumor. Except for the nonfunctioning islet cell tumor, each secretes an identifiable hormone in the serum to produce a distinct syndrome.

Gastrinoma has alpha cell origin and produces gastrin which stimulates hydrochloric acid release from the parietal cells of the stomach. With prolonged uninhibited acid secretion, patients develop Zollinger-Ellison syndrome with severe peptic ulcer disease and often with associated diarrhea, vomiting, or gastrointestinal bleed. Occasionally patients will have low acid levels or achlorhydria. The pancreatic lesions are malignant in 60% of cases, benign adenomas in 30%, and hyperplastic in 10%. In half of the patients, the lesions are solitary and limited to one anatomic area of the pancreas with a head:body:tail ratio of 4:1:4. Multiple lesions involving two areas occur in 30% of patients and involve the entire gland in 20% of patients. In addition, ectopic gastrin-producing tumors have been reported and can include the wall of the stomach or duodenum, omentum, lymph node and ovary.

Typical findings on UGI examintaion show gastric rugal hypertrophy, duodenal mucosal fold hypertrophy, hypersecretion with barium dilution, and multiple ulcers, some in unusual places such as the distal duodenum and proximal jejunum. On abdominal CT, islet cell tumors measure less than 2 cm 90% of the time. They enhance homogeneously with intravenous contrast, lack central necrosis or cystic degeneration, demonstrate no vascular encasement, and contain calcifications 20% of the time. Often, malignant tumors have hepatic or regional lymph node metastases at presentation. On MR imaging, gastrinomas usually have a low-to-intermediate signal on T1-weighted images and high signal on T2-weighted images although some islet cell tumors show an intermediate T2 signal. An early study on using MR imaging for detecting gastrinomas demonstrated that CT was more effective than MR. However, more recent studies suggest that MR has a higher sensitivity and specificity than CT in detecting small pancreatic tumors. The role of MR in the imaging of pancreatic neoplasms is still under investigation.

Complete surgical resection of early solitary lesions offers the best prognosis for cure. When the lesions are not amenable to complete surgical resection, symptomatic relief can be achieved with H-2 antagonists or omeprazole. In advanced disease, streptozocin and fluorouracil combination is the standard chemotherapy. Octreotide acetate, a somatostatin analogue, has shown early promise as an antineoplastic agent in long term suppression of elevated gastrin levels and will require more extensive clinical testing.

References

Eisenberg RL. Gastrointestinal radiology: a pattern approach. Philadelphia: JB Lippincott Co, 1990: 348-352.

Friedman AC. Pancreatic neoplasms and cysts. In: Friedman AC and Dachman AH, editors. Radiology of the liver, biliary tract and pancreas. St. Louis: Mosby-Year Book, Inc, 1994: 807-934.

Frucht H, Doppman JL, Norton JA, Miller DL, Dwyer AJ, Frank JA, Vinayek R, Maton PN, Jensen RT. Gastrinomas: comparison of MR imaging with CT, angiography, and US. Radiology 1989; 171: 713-717.

Moertel CG, Lefkopoulo M, Lipsitz S, Hahn RG, Klaassen D. Streptozocin-doxorubicin, streptozocin-fluorouracil or chlorozotocin in the treatment of advanced islet-cell carcinoma. New England Journal of Medicine 1992; 326(8): 519-523.

Muller MF, Meyenberger C, Bertschinger P, Schaer R, Marincek B. Pancreatic tumors: evaluation with endoscopic US, CT, and MR imaging. Radiology 1994; 190: 745-751.

Saltz L, Trochanowski B, Buckley M, Heffernan B, Niedzwiecki D, Tao Y, Kelsen D. Octreotide as an antineoplastic agent in the treatment of functional and nonfunctional neuroendocrine tumors. Cancer 1993; 72(1): 244-248.

Semelka RC, Cumming MJ, Shoenut JP, Magro CM, Yaffe CS, Kroeker MA, Greenberg HM. Islet cell tumors: comparison of dynamic contrast-enhanced CT and MR imaging with dynamic gadolinium enhancement and fat suppression. Radiology 1993; 186: 799-802.

Thompson NW, Bondeson AG, Bondeson L, Vinik A. The surgical treatment of gastrinoma in MEN I syndrome patients. Surgery 1989; 106(6): 1081-1085.

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