Medullary carcinoma of the small intestine is an exceedingly rare tumor. These tumors account for less than 0.04% of all colorectal cancers and only one case to date has been reported in the ileum. Although the clinical manifestations can be consistent with signs of intestinal obstruction, often times they are discovered incidentally in an asymptomatic patient. Major contributing risk factors to the development include long standing inflammation such as Crohn's disease, and other chronic inflammatory illnesses. Tumor markers and imaging can aid in the diagnosis, however biopsy is needed for definitive diagnosis. Despite the fact that the development of these tumors in the ileum is rare, further enhancement of awareness can aid in the appropriate early detection and appropriate treatment modalities.

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INTRODUCTION: Intussusception is a process in which a segment of bowel telescopes into the adjoining intestinal lumen. The pathophysiology is unclear but it is typically due to a pathologic lead point within the bowel, which is malignant in over 50% of cases. The clinical presentation of adult intussusception is non-specific, unlike the characteristic triad of abdominal pain, palpable abdominal mass, and bloody stool seen in pediatric patients. It is a rare cause of abdominal pain in adults, comprising only 5% of all intussusceptions. CASE DESCRIPTION/METHODS: A 29-year-old Peruvian male with no significant medical history presented with right lower quadrant abdominal pain and diarrhea for two weeks with an unintentional 15 pound weight loss. Abdominal CT demonstrated intussusception with likely underlying mass in the region of the ileocecal valve. Colonoscopy revealed an ileocecal mass (Figures 1 and 2) that was too large to pass with the endoscope. The patient subsequently underwent a right hemicolectomy and omental flap. Pathology of the mass showed diffuse large B-cell lymphoma (DLBCL), germinal center type. Further evaluation revealed a positive HIV test with a CD4 count of 29 cells/mL. DISCUSSION: Adult intussusception is a rare clinical entity and requires prompt imaging and diagnosis to prevent severe complications. A retrospective review of 44 cases found that ultrasound and CT resulted in a combined preoperative diagnosis rate of 95.5%. Literature review suggests surgical resection is the optimal management in adults given the high incidence of underlying malignancies. Controversy remains regarding the ideal surgical approach between primary resection versus reduction followed by resection. Several retrospective studies propose resection without reduction is the best approach for ileocecal intussusception to avoid potential intraluminal seeding or venous tumor dissemination. Our patient was diagnosed via CT and treated by surgical resection without complications. Further diagnostic workup revealed the etiology to be a DLBCL in the setting of HIV/AIDS. This case highlights the importance of identifying an underlying mechanism for the development of intussusception in young adults. The incidence of primary lymphoma in the small intestine is rare and accounts for 1-4% of all gastrointestinal malignancies and 10-20% of small intestine malignancies. Through this case presentation, we hope to contribute to the limited available data on cases of adult intussusception.

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