The islet cell tumor in VHL may be unrelated to pancreatic cystic disease. It occurs more frequently in patients with pheochromocytomas (72,99,100). Probst et al and Hull et al believe that the islet cell tumor derives from amine precursor uptake and decarboxylation (APUD) cells and calls islet cell tumors of the pancreas, APUDomas (101,102). Like the pheochromocytoma, APUDomas probably are of neural crest origin (101,103). Nonetheless, some "overlap" patients will exhibit both mild pancreatic cystic disease and islet cell tumors (72,75).
The islet cell tumor consists of nests of polygonal cells with vesicular nuclei (18). Most islet cell tumors are slow growing and asymptomatic but lesions can grow rapidly, cause biliary obstruction and metastasize to the liver or more distantly to the bone (50). Three of six islet cell tumors in one series were metastatic (75). A number of endocrinopathies have been associated with these tumors including pancreatic polypeptide, "protein gene product" (13), vasoactive intestinal polypeptide (VIP) (75,105), calcitonin (104), insulin and glucagon (101), gastrin and somatostatin (101).
Unlike pancreatic cystic disease, islet cell tumors commonly show intense enhancement on CT and may contain calcification (Figure 14).
Figure 14. A symptomatic patient with pheochromocytoma and islet cell tumor of the
pancreas. A small right pheochromocytoma with a necrotic center (P) is seen.
In addition, an intensely enhancing mass is present in the neck of the pancreas
(I). Two small pancreatic cysts are also seen but the bulk of the pancreas
is spared. Pancreatic islet cell tumors are associated with pheochromocytomas
and are generally not accompanied by cystic pancreatic disease.As the tumor enlarges areas of necrosis may be seen. Intraoperative ultrasound may be useful in identifying focal masses if an attempt is made to "shell out" such lesions rather than perform a pancreatectomy. Angiography is useful in localizing pancreatic islet cell tumors.
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