Routine Screening Colonoscopy Reveals Appendiceal Mucin: Uncovering a Low-Grade Appendiceal Mucinous Neoplasm

CASE REPORT A 66-year-old asymptomatic man with no family history of colorectal cancer underwent his first screening colonoscopy, revealing a 7 mm tubular adenoma, a 4 mm hyperplastic polyp, sigmoid diverticulosis, and a patulous appendiceal orifice with extrusion of mucoid material into the cecal lumen (Figures 1–4). Biopsies of the appendiceal orifice rim demonstrated features consistent with a sessile serrated adenoma. Subsequent computed tomography scan showed a nondilated normal-appearing appendix with 5 mm diameter and no evidence of a mucocele. Laparoscopic appendectomy with excision of a small portion of the cecum was performed. Pathological examination revealed the appendix to be involved with both a sessile serrated lesion in the proximal portion and a low-grade appendiceal mucinous neoplasm in the distal portion, with an intervening section of normal-appearing appendix between the 2 lesions. The distal low-grade appendiceal mucinous neoplasm was likely responsible for the mucin identified endoscopically protruding from the appendiceal orifice. This represents an extremely rare case, infrequently described as being detected by colonoscopy.1 The incidence of appendiceal mucinous neoplasms is estimated at 0.12 cases per 1 million people per year.2 The most common clinical presentation is acute appendicitis, with complications including pseudomyxoma peritonei and enterocolonic fistula formation.3,4Figure 1.: Colonoscopy reveals appendiceal mucin.Figure 2.: High power view of sessile serrated lesion without dysplasia.Figure 3.: Low-grade appendiceal mucinous neoplasm in distal appendix.Figure 4.: Higher magnification of low-grade appendiceal mucinous neoplasm with low-grade dysplasia.DISCLOSURES Author contributions: PP Mark contributed to conceptualization, writing—original draft, writing—review & editing; L. Hixson contributed to conceptualization, supervision, writing—original draft, writing—review & editing. Financial disclosure: None to report. Informed consent was obtained for this case report.