Islet Cell Tumors of the Pancreas

Clinical, Radiologic, and Pathologic Correlation in Diagnosis and Localization

Abstract Introduction and Historical Perspective Clinical Features

Pathologic and Histologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

Summary Source Information References

Pathologic and Histologic Features

Small islet cell tumors tend to be well demarcated, solid, and firm to rubbery on palpation. Their color is variable, depending on the amount of stroma, the degree of vascularity, and the presence of hemorrhage or cystic degeneration, and may range from pale yellow to pink or red. Larger islet cell tumors tend to demonstrate cystic changes and necrosis. Gritty calcification may also be seen in the larger tumors.

The histologic characteristics of functioning and clinically silent lesions are identical. Three patterns are observed: (a) a solid, diffuse pattern; (b) a ribbonlike, trabecular pattern; and (c) an acinar or ductlike pattern (Figure 1). More than one of these architectural patterns may occur in the same neoplasm. Islet cell tumors are composed of sheets of small round cells. Mitoses are unusual. The amount of intervening stroma is extremely variable, and the stroma may appear dense and hyalinized. There is a well-organized relationship between the neoplastic cells and the numerous stromal vessels. These vessels are responsible for the hypervascular nature of the lesions.

Immunohistochemical staining does not allow differentiation among the different types of functioning islet cell tumors nor does it allow reliable separation between functioning and clinically silent tumors. All islet cell tumors are capable of elaborating more than one hormone in different parts of the same tumor. Different degrees of hormone production may be seen within different cells in the same portion of a tumor as well (20,21). The majority of patients, however, have symptoms related to overproduction of a single hormone or have no hormone-related symptoms at all (22).

Smaller tumors, typically insulinomas or gastrinomas, tend to be homogeneous masses without local invasion. Insulinomas are usually benign (90% of cases), solitary (90%), intrapancreatic (99%) masses (8). On the other hand, over 60% of patients with gastrinomas present with metastases. Up to 30% of gastrinomas are located outside the pancreas, usually in the duodenum (23). Multiple gastrinomas are common (4). Other functioning and clinically silent islet cell tumors are usually intrapancreatic and are larger than gastrinomas or insulinomas. Larger tumors more commonly demonstrate cystic changes, necrosis, calcification, local invasion, vascular invasion, and distant metastases. The larger tumors are usually clinically silent. Multiple islet cell tumors are common in the setting of MEN type I but otherwise are unusual.

Abstract Introduction and Historical Perspective Clinical Features

Pathologic and Histologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

Summary Source Information References