Intussusception caused by primary malignant melanoma of the small intestine.

Whether melanoma develops as a primary tumor in the small bowel remains controversial. A 57-year-old male Japanese presented signs of intestinal obstruction. Ultrasonography and computed tomography disclosed an abdominal mass with multiple concentric rings, characteristic of intussusception. At surgery, a spherical tumor, 3.8 cm in diameter, with scattered pigmentation was found to lead the intussusception. Segmental intestinal resection with regional lymph node dissection was performed. Pathological examination revealed diffuse infiltration of malignant melanoma cells. Nodal metastasis was seen only in the mesenteric node draining from the tumor-bearing intestinal segment. Twelve months after surgery, melanoma recurred in the liver and para-aortic lymph nodes, where a malignancy of the digestive organs frequently metastasizes; however, no extraperitoneal melanoma was found after repeated examinations. Thus, this case suggests that primary malignant melanoma can originate in the small intestine and be a cause of intussusception in the adults.