Metastatic Melanoma in the Small Bowel

Teddy Jinnteh Su, MD - Case Coordinator
John Walter Millstine, MD - Radiology Discussion
Henry D Haskell, MD - Pathology Discussion
Pablo R Ros, MD, MPH - Attending Radiologist

January 13, 2003

Presentation

Imaging Findings

Contrast enhanced images through the pelvis/lower abdomen show loops of small bowel. In the right lower quadrant there is thickening of the bowel wall, and contrast is visible through the lumen. In the left abdomen, there is another thickened loop with some fat stranding. Lower down, the fat in the mesentery seems well maintained; no fluid is visible. The vessels appear to be normal. In summary, there are two focal areas of thickened, distal small bowel. This suggests an obstruction, perhaps caused by a mass.

Differential Diagnosis

Diagnosis

Discussion

The gross image shows a large polypoid mass from the small bowel. On a low-power microscopic image, the extreme cellularity and high degree of irregularity/pleiomorphism are apparent. The tumor is highly vascular, as evidenced by the large number of angiogenic vessels. The first high-power image demonstrates an S-100 immunohistochemical stain. S-100 is one of two principal immunohistochemical stains used in the diagnosis of melanoma; it is the older of the two and has high sensitivity. HMB-45 is typically more specific, but was negative in this case. The second high-power image is a sample stained with hematoxylin and eosin. This image creates significant suspicion of melanoma (separate from the patient’s history of melanoma, which was not shared at the outset), in that it reveals prominent nucleoli and a decidedly epithelioid appearance (scant spindle cells notwithstanding).

Radiology Discussion

Primary tumors of the small bowel are rare, accounting for only 2-3% of gastrointestinal tumors. The incidence of benign vs. malignant tumors is about even, unless the patient is symptomatic. In the presence of clinical symptoms, malignant tumor is roughly 3 times more likely. Small bowel primaries, in order of relative frequency, include carcinoid (often seen in the terminal ileum; profound desmoplastic reaction and calcification are typical), adenocarcinoma, lymphoma (often causes aneurismal dilatation of the bowel), GI stromal tumor, vascular malignancy, and fibrosarcoma. Metastatic disease of the small bowel, on the other hand, is relatively common.

Metastases spread to the small bowel by three processes. Intraperitoneal seeding is most common with a primary tumor in the appendix, colon, or female reproductive tract. Metastases arise from deposits along the mesenteric surface with increased frequency in ileum. Direct extension can occur from tumors in the prostate, pancreas, colon, kidney, or female reproductive tract. Hematogenous metastasis can occur in the presence of melanoma, primary tumors of the breast, lung or colon, Kaposi’s sarcoma, or embryonal cell carcinoma of testes. Metastatic lesions arising from hematogenous spread are typically found in submucosal or antimesenteric locations.

Melanoma is composed of melanocytes of neuroectodermal origin. It is the 6th most common cancer in the United States, and incidence is increasing. The most common sites of primary occurrence include skin, oral and anal mucosa, eyes, esophagus, and meninges. Melanoma metastasizes via lymphatic and hematogenous routes, typically to the liver, lung, bone, and brain. If metastases occur in the GI tract, the most common sites include the small bowel (50%), colon (32%), and anorectum (25%). Some unusual metastatic sites have been reported, such as the heart. Following treatment, melanoma may have ultra-late (>15 years) recurrence. Metastases in the small bowel indicate advanced disease with poor prognosis.

References

Brant W, Helms C. Fundamentals of Diagnostic Radiology. 2nd ed. Baltimore:Williams and Wilkins; 1999.

Dahnert W. Radiology Review Manual. 4th ed. Baltimore:Williams and Wilkins; 1999.

Riegel D, et al. The incidence of malignant melanoma in the United States: issues as we approach the 21st century. J Am Acad Dermatol. 1996;34:839.

Tsao H, et al. Ultra-late recurrence of cutaneous melanoma. Cancer. 1998;82:1799-1800.

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