Non-functioning Pancreatic Endocrine Tumor

Joshua Lee Rosebrook, MD - Case Coordinator
Mylinh D Huynh, MD - Radiology Discussion
Gerald P Bailey, MD, PhD - Pathology Discussion
Pablo R Ros, MD, MPH - Attending Radiologist

August 12, 2002

Presentation

Imaging Findings

The bone scan demonstrates a focus of increased uptake over the ninth anterior left rib. Roughly symmetrical increased uptake in the shoulders is likely due to degenerative changes. This suggests a possible primary tumor or bony metastasis with pathologic fracture. No plain film was available for review.

On abdominal computed tomography (CT), the tail of the pancreas seems prominent--as though a soft tissue mass is expanding the structure. No associated adenopathy or other identifying characteristics are evident. The mass appears to be solid, with a small area of slightly lower intensity that suggests necrosis or a minor cystic component. The tail is approximately isointense to the rest of the pancreas.

Differential Diagnosis

Diagnosis

Discussion

No data from an endocrine battery were available. A pancreatectomy was performed. A solitary, firm lesion is located at the distal end of the pancreas. The mass is tan and homogeneous; there is no necrosis or hemorrhage. The size of the mass (3 cm) is suggestive of malignancy (benign tumors tend to be 2 cm or less), although the definitive factor is vascularization. A rim of normal pancreatic parenchyma surrounds the mass. The tumor is composed of trabecular chords of atypical cells with dense stroma. No vascularization is visible. The tumor cells were positive for neuroendocrine markers, but negative for insulin. It is most likely a non-functioning (benign) islet cell tumor.

Radiology Discussion

The differential diagnosis of a cystic pancreatic mass includes:

• Pseudocyst/congenital cyst, which is benign.
• Serous cystadenoma, a microcystic mass in the pancreatic head characterized by hypervascularity, central scar, and, occasionally, calcification and/or hemorrhage. These occur most commonly in older patients and are benign.
• Mucinous cystadenoma, a relatively large (6-10cm), macrocystic mass (generally [85%] located in the tail or body of the pancreas) that occurs most commonly in females with a peak incidence in the 4th and 5th decades. This is a lobulated mass with a fibrous capsule, mural nodules and calcifications may be present. These masses are hypo- or avascular and have malignant potential.
• Solid pseudopapillary neoplasms are usually located in the pancreatic tail. They occur most commonly in young females, and, in spite of hypervascularity, are generally benign or low grade.
• Intraductal papillary mucinous neoplasms are most common in older males; the prognosis with this diagnosis is excellent.
• Choledochocele, which is benign.

The differential diagnosis for a solid pancreatic mass includes

• Adenocarcinoma, a hypovascular lesion that often (66%) occurs in the pancreatic head, has a slight male predominance (60%) and is more common in blacks than Caucasians. These represent approximately 85% of pancreatic masses.
• Lymphoma, which is rare but not uncommonly seen at autopsy in cases of non-Hodgkin’s lymphoma (1/3 of cases); at autopsy, it is difficult to distinguish whether a mass is primary or the result of tumor infiltration from peripancreatic nodes.
• Islet cell/ endocrine tumor, which is hypervascular and may have malignant potential. These represent approximately 10% of pancreatic masses.
• Metastasis, which is rare but can occur with melanoma as well as breast and bronchogenic carcinoma.

There are several types of islet cell (endocrine) tumors of the pancreas. The most common is insulinoma, a B-cell type with low (10%) malignant potential; hypoglycemia is a common symptom. Gastrinoma is a G-cell type with greater (60%) malignant potential; patients often present with severe peptic ulcers. Glucagonoma is a relatively highly malignant (80%) A-cell type that is associated with diabetes mellitus; necrotizing migratory erythema is a common symptom. Somatostatinoma is the least common type, and patients generally present with non-specific symptoms (e.g., steatorrhea, diabetes); 60% of cases are malignant. Most vipomas are malignant; watery diarrhea and hypokalemia are common symptoms. The most malignant type (90%), the non-functional islet cell tumor, is also the most common type (represents one-third of endocrine tumors of the pancreas).

The benign vs. malignant nature of an islet cell tumor is often diagnosed based on clinical behavior, rather than strictly upon its histology. All of the types involve abnormal cells with some malignant potential. Therefore, it is important to look for clinical and pathologic evidence of malignancy: metastatic disease, lymph node involvement, vascular invasion. Radiologists, therefore, are often the ones indicating prior to surgery the malignant nature of such a tumor, due to the discovery of metastases or enlarged lymph nodes. Morphologically, in the past 10 years, has been found to be a good prognostic indicator; larger tumors are more likely to be malignant than smaller tumors. Heterogeneity is also an indicator; more areas of necrosis and hemorrhage indicate a higher likelihood of malignancy. Calcification, which is often associated with benign tumors, is an indicator of malignancy in islet cell tumors.

In the case presented, the possibility of a rib lesion remains an open question. It is unlikely, however, that a pancreatic mass would metastasize to bone. The apparently solitary lesion is especially unlikely to be metastatic. No follow-up on the potential rib lesion was presented.

References

Crump et al. Lymphoma of the Gastrointestinal tract. Seminars in Oncology 1999:26: 324-337

Menegaux et al. Pancreatic Insulinoma. American Journal of Surgery 1993; 165:243- 248.

Box et al. Management of cystic neoplasm of the pancreas. American Journal of surgery, 2000 May; 66(5): 495-501.

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