When Two Rarities Occur, The Bowel Cringes

INTRODUCTION: Intussusception is a rare cause of mechanical intestinal obstruction in adults and is more frequently observed in pediatric patients. It tends to occur in association with a pathologic lead point, in most cases, a malignancy. Malignancies that commonly cause intussusception include lymphoma, colonic adenocarcinoma, and metastatic melanoma. Primary intestinal melanoma, however, is extremely rare and here we describe a case that presented as intussusception. CASE DESCRIPTION/METHODS: A 64-year-old female with asthma, COPD, OSA, HTN, HLD, GERD presented with a one week history of abdominal pain and nausea that progressed to coffee-ground emesis and melena a few days prior to admission. She endorsed a 22 pound unintentional weight loss and initial exam showed a soft but diffusely tender abdomen with labs only significant for a normocytic anemia that was near baseline. Computed tomography (CT) of the abdomen revealed intussusception and wall thickening involving the proximal small bowel (Figure 1). A small bowel enteroscopy demonstrated a 3-4 cm ulcerated, non-circumferential, non-obstructing mass in the proximal jejunum (Figure 2). A few non-bleeding superficial jejunal ulcers in the surrounding area which were presumed ischemic from the intussusception were also noted. Biopsies were sent for pathology and revealed sheets of infiltrating malignant cells with moderate amphiphilic cytoplasm and enlarged nuclei, some with pseudo inclusions. Immunohistochemical staining was done and the tumor cells stained positive for S100 and MelanA/MART1 and negative for CK7, CK20, CDX12, and CD45 which was concerning for metastatic melanoma (Figure 3). Patient underwent exploratory laparotomy with excision of the jejunal mass with surgical pathology confirming a malignant melanoma. Extensive imaging and examination of all cutaneous surfaces did not reveal a primary source. The patient was deemed to have a primary small bowel melanoma. DISCUSSION: Primary small bowel melanoma is extremely rare and should always be on the differential for neoplasms that can cause intussusception. Most intestinal melanomas represent metastatic disease and definite diagnosis can only be made after thoroughly excluding a primary lesion. It is important to recognize primary mucosal melanomas, as they are more aggressive and carry a worse prognosis, partly due to late diagnosis. Early recognition and diagnosis may allow for curative resection of the tumor, which remains the treatment of choice.Figure 1.: Proximal jejunal intussusception.Figure 2.: Push enteroscopy showing proximal jejunal mass.Figure 3.: Top left, immunohistochemical stain positive for s100. Top right, immunohistochemical stain positive for MelanA. Bottom left, H&E stain showing malignant cells with lymphovascular invasion. Bottom right, H&E stain, high power showing amphophilic cytoplasm, pleomorphic nuclei, and numerous mitotic figures.