Primary small bowel melanomas: fact or myth?

Abstract

Small bowel melanoma (SBM) is a rare entity, which often evades diagnosis and therefore presents late. Its origin, whether arising primarily or metastatically from an unidentified or regressed primary cutaneous melanoma, remains debatable. In this report, we present a rare case of primary SBM and review the current literature. A 60-year-old man presented with melena and microcytic anemia. A series of investigations including abdominal ultrasonography (US), esophago-gastro-duodenoscopy (EGD) and colonoscopy were normal. Abdominal computed tomography revealed no specific pathology. Subsequent capsule endoscopy identified a jejunal mass, which was confirmed on laparotomy, was resected, and histologically diagnosed as melanoma. Extensive postoperative clinical examination revealed no cutaneous lesions. This report discusses gastrointestinal (GI) malignant melanoma, and examines the evidence both for and against the existence of true primary vs. metastatic disease. Furthermore, this case highlights the capabilities of capsule endoscopy in identifying an extremely rare GI tumor, which evaded other diagnostic modalities. Finally, the origins and pathophysiology of this rare cancer are evaluated, with the aim of promoting early diagnosis and treatment, and therefore improving current poor outcomes.

Keywords: Bowel; capsule; endoscopy; intestine; melanoma.

Figure 1

Abdominal CT demonstrating annular small bowel thickening and mesenteric lymphadenopathy.

Figure 2

Capsule endoscopy views of small bowel tumor (annotated).

Figure 3

Capsule endoscopy video showing the sessile small bowel tumour (1). Available online: http://www.asvide.com/articles/947

Figure 4

Immunohistochemistry of tumor biopsy revealing melanoma cells. (A) H&E staining (×100); (B) positive S100 staining (×100).

Figure 5

Lymph node architecture replaced by invading malignant melanoma cells with capsular breach (H&E staining; ×10).