Acute abdominal presentation of mantle cell lymphoma mimicking acute appendicitis: a case report.

Lymphoma presenting as an acute abdomen is rare in adults and is more commonly seen in children, particularly with Burkitt or diffuse large B-cell lymphoma. Approximately 1 per cent of appendicectomy specimens contain neoplasms, with only a very small proportion (~0.015 per cent) representing primary appendiceal lymphomas. A man in his 50s with no prior history of malignancy presented with a two-day history of right iliac fossa pain. Computed tomography demonstrated features consistent with acute appendicitis, without features suggestive of malignancy. A laparoscopic appendicectomy was performed without complication. Histopathological examination confirmed acute transmural appendicitis and mantle cell lymphoma (MCL) involving the appendiceal lymphoid tissue. The lymphoma was non-mass-forming and would likely have remained undetected without routine immunohistochemical analysis. This report describes a rare presentation of previously undiagnosed MCL identified alongside acute appendicitis, highlighting the importance of routine histopathological examination, even when intraoperative and radiological findings are consistent with uncomplicated appendicitis.