Incidental diagnosis of primary appendiceal follicular lymphoma following appendectomy.

INTRODUCTION: Primary appendiceal lymphoma is exceptionally rare, representing approximately 0.015% of all gastrointestinal lymphomas and 1.7% of appendiceal tumors. Most cases are non-Hodgkin lymphomas, with diffuse large B-cell lymphoma being the predominant histological subtype. Follicular lymphoma of the appendix is particularly uncommon and is frequently diagnosed only after surgical resection. CASE PRESENTATION: A 76-year-old Caucasian male presented with a two-day history of fever and abdominal pain migrating to the right iliac fossa. Laboratory investigations revealed mild leukocytosis and elevated inflammatory markers. Abdominal ultrasonography demonstrated an enlarged appendix measuring 15 mm in diameter, associated with periappendiceal fat stranding and free fluid, consistent with acute appendicitis. The patient underwent laparoscopic appendectomy, which revealed gangrenous and perforated appendicitis with diffuse purulent peritonitis. One week after surgery, he developed a left popliteal deep vein thrombosis and was started on anticoagulation therapy. Histopathological examination of the appendiceal specimen unexpectedly demonstrated grade 1-2 follicular lymphoma. Subsequent colonoscopy revealed terminal ileal involvement by lymphoma. Following multidisciplinary evaluation, a watchful waiting strategy was adopted, and the patient remains under regular oncological surveillance. DISCUSSION: Primary appendiceal lymphoma is an extremely rare malignancy that most commonly presents as acute appendicitis, making preoperative diagnosis challenging. Although diffuse large B-cell lymphoma is the most frequently reported subtype, follicular lymphoma accounts for a small minority of cases and generally follows an indolent clinical course. This case highlights the diagnostic challenges posed by primary appendiceal follicular lymphoma and underscores the importance of routine histopathological examination of appendectomy specimens.