Beyond the Watershed: Chronic Ischemic Colitis Masking Underlying Small Bowel Non-Hodgkin Lymphoma.

Ischemic colitis (IC) most commonly affects the watershed regions of the left colon, whereas right-sided involvement is less common but associated with higher morbidity, mortality, and a greater likelihood of requiring surgery. Atypical presentations, especially when driven by underlying pathology, demand heightened clinical suspicion. We present a case of right-sided colonic ischemia in a patient with brief hemodialysis exposure who was later found to have aggressive B-cell lymphoma involving the bowel. A 64-year-old woman with hypertension, hyperlipidemia, prior cerebrovascular accident, peripheral arterial disease, chronic gastroesophageal reflux disease, and autosomal dominant polycystic kidney disease presented with one month of intermittent crampy abdominal pain. In 2024, she had undergone outpatient hemodialysis for three months before receiving a kidney transplant. On admission, her vital signs were stable. Laboratory evaluation revealed leukocytosis (15.2 × 10³/μL), hemoglobin 12.0 mg/dL, baseline creatinine 1.8 mg/dL, and normal lactic acid. Computed tomography of the abdomen and pelvis showed mural thickening of the cecum and ascending colon with pericolonic stranding. Colonoscopy demonstrated diffuse friability and continuous ulceration in the proximal colon concerning for right-sided IC. Exploratory laparotomy revealed an ischemic, perforated cecum, an omental mass, and small bowel tumors. Right hemicolectomy with end ileostomy was performed, and pathology confirmed high-grade B-cell lymphoma. She required intensive care with vasopressors and mechanical ventilation and was treated for cytomegalovirus viremia with intravenous ganciclovir followed by valganciclovir. Gastric biopsy confirmed diffuse large B-cell lymphoma with c-Myc rearrangement. Right-sided IC carries increased risk of transmural necrosis and sepsis, particularly in patients with vascular disease, immunosuppression, or prior dialysis. Primary intestinal lymphoma can mimic IC through obstruction and microvascular compromise. Early recognition of atypical right-sided IC is essential, as prompt surgery and biopsy can identify underlying malignancy and guide timely oncologic management.