Primary Diffuse Large B-cell Lymphoma of the Terminal Ileum Presenting With Bowel Perforation and an Acute Abdomen in an Elderly Patient.

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma; however, primary involvement of the small intestine is uncommon. Acute bowel perforation is a rare and life-threatening presentation that may mimic more common causes of acute abdomen. We report the case of a 78-year-old woman who presented with worsening abdominal pain, nausea, vomiting, and obstipation. Computed tomography demonstrated pneumoperitoneum concerning for hollow viscus perforation. Exploratory laparotomy revealed a perforated terminal ileal mass, and segmental small bowel resection was performed. Histopathologic evaluation demonstrated diffuse transmural infiltration by large atypical lymphoid cells with diffuse CD20 positivity and MUM1 nuclear positivity, consistent with DLBCL, non-germinal center B-cell subtype by the Hans algorithm (CD10-negative, BCL6-positive, MUM1-positive). The postoperative course was complicated by sepsis, respiratory failure, and prolonged ileus. This case highlights the importance of considering primary gastrointestinal lymphoma in the differential diagnosis of bowel perforation and acute surgical abdomen, particularly in elderly patients presenting emergently.