S3678 Acute Appendicitis or Something More? High-Grade B-Cell Non-Hodgkin’s Lymphoma Presenting as Appendicitis in a Young Adult

Introduction: Primary appendiceal lymphomas are rare, accounting for <1% of gastrointestinal (GI) lymphomas. They often present as acute appendicitis, with diagnosis typically made postoperatively via histopathology. We present a case of a young man diagnosed with high-grade B-cell non-Hodgkin’s lymphoma, not otherwise specified (HGBL-NOS) of the appendix following laparoscopic appendectomy. Case Description/Methods: A 25-year-old man presented with 24 hours of abdominal pain, nausea, and vomiting. Exam revealed percussive tenderness, guarding, and rigidity. Labs were notable for leukocytosis (15.8 × 109/L) and elevated CRP (445 mg/L). computed tomography abdomen/pelvis with IV contrast demonstrated an inflamed tubular structure extending from the cecum, 5.9 cm abscess formation, and mesenteric lymphadenopathy. Laparoscopic appendectomy revealed a necrotic, ruptured appendix adherent to the terminal ileum. Histopathology showed sheets of lymphoma cells with a starry-sky pattern, high Ki-67 index (∼100%), and immunophenotypic features consistent with HGBL-NOS. Positron emission tomography-computed tomography (PET-CT) revealed FDG-avid mesenteric lymph nodes without distant metastasis, and bone marrow biopsy was negative. The patient was initiated on systemic R-CHOP chemotherapy. Discussion: Primary appendiceal lymphoma is an exceedingly rare GI malignancy (0.015% of GI lymphomas), often mimicking acute appendicitis. Gastroenterologists play a key role in recognizing atypical CT findings, including a bulky, homogeneously enhancing appendiceal mass with mesenteric lymphadenopathy, which may suggest lymphoma rather than typical appendicitis. In such cases, early gastroenterology consultation can guide further evaluation, including colonoscopy to assess for synchronous GI involvement or endoscopic ultrasound (EUS) if an appendiceal mass is detected. Histopathology confirmed HGBL-NOS in our case, an aggressive but treatable malignancy. Although surgery addressed the acute disease, ongoing gastroenterology surveillance is crucial for recurrence or secondary GI involvement. This case underscores the importance of histopathologic evaluation of appendectomy specimens and the need for gastroenterologists to recognize atypical presentations of GI malignancies, as early suspicion may influence evaluation options, prognosis, and long-term management.