S1684 Appendiceal Adenomatous Mucocele Masquerading as Right-Sided Colonic Diverticulitis

Abstract

INTRODUCTION: Appendiceal mucoceles (AM) are found in 1% of appendiceal specimens. AM are often incidental imaging findings and are often not visible on routine colonoscopy. They are usually asymptomatic, but can present with right lower quadrant (RLQ) pain, palpable mass, weight loss and altered bowel habits- often mimicking appendicitis. We present a rare case of adenomatous AM masquerading as right sided diverticulitis. CASE DESCRIPTION/METHODS: 56 yo man with GERD, chronic constipation, and prior colonic adenomas presents with 48 hrs of non-bloody diarrhea, RLQ pain and fever of 101F; denies chills, nausea, vomiting. Exam: soft, non-distended abdomen, hypoactive bowel sounds, RLQ tenderness with mild rebound. Labs: mild leukocytosis. Imaging: CT A/P shows cecal wall thickening and fat stranding consistent with right sided diverticulitis, no evidence of appendicitis. Patient responded to ciprofloxacin and metronidazole, but presented 2 months later with intermittent RLQ pain, similar but less severe to initial presentation. Colonoscopy revealed an appendiceal rim with a 10 mm adenomatous appearing polyp prolapsing from deep in the orifice; no right sided diverticula were visualized. Patient underwent appendectomy with partial cecectomy and recovered well. Surgical pathology revealed a 1.5 cm adenomatous polyp of the appendix. DISCUSSION: There are various classification systems for AM. The PSOGI consensus criteria describes eight distinct lesion categories: adenoma, serrated polyp, LAMN (low grade neoplasm of the appendix), HAMN (high grade appendiceal mucinous neoplasm), mucinous adenocarcinoma, signet ring cell low differentiated adenocarcinoma, signet ring cell carcinoma and adenocarcinoma. Surgical resection is critical to ascertain lesion type and develop adjunctive therapy and follow up. AM may result in pseudomyxoma peritonei, a fatal condition of copious mucinous or gelatinous ascites. Thus, regardless of classification, surgical resection is indicated for all appendiceal polyps. Initial imaging studies misdiagnosed our patient with right sided diverticulitis. However, colonoscopy with direct mucosal visualization revealing an adenomatous polyp extruding from the appendiceal orifice facilitated the correct diagnosis of AM. Therefore, although rare, appendiceal neoplasms should be considered in cases of RLQ pain and imaging suggestive of acute inflammatory response; colonoscopy is essential for ongoing RLQ pain and presumed right sided diverticulitis to rule out both colonic and appendiceal neoplasms.Figure 1.: Appendiceal polyp.