Acellular mucin in non-neoplastic inflammatory conditions of lower gastrointestinal tract

Purpose: In the context of neoplasia, acellular mucin in lower gastrointestinal (GI) tract implies occult mucinproducing tumor and warrants additional workup. The clinical significance of acellular mucin in benign conditions remains unclear. Methods: Lower GI tract surgical specimens with acellular mucin without documented neoplastic conditions (colonic diverticulitis (n = 16), appendicitis (n = 14), and others (n = 8)) were retrieved. Low grade appendiceal mucinous neoplasm (LAMN) (n = 24) and diverticulitis without acellular mucin (n = 28) were used as controls for appendicitis and diverticulitis cases, respectively. Clinical data, histological findings, and additional workups performed due to acellular mucin were collected. Results: Patients with appendicitis with acellular mucin frequently presented with signs and symptoms of acute appendicitis (p = 0.016) compared to LAMN. 71 % were interval appendectomy, and 57 % had diverticula. In colonic diverticulitis cohort, no differences were found in terms of the duration of symptoms, age, gender and the degree of inflammation between the groups with and without acellular mucin. Seven of 8 patients with other conditions with acellular mucin had a history of abdominal surgery or fistula. Additional workup included levels (n = 7), consults (n = 11), and stains (n = 4). Conclusion: Acellular mucin can be seen in a variety of benign conditions but this phenomenon is probably underrecognized and leads to additional investigations. Acellular mucin is likely translocated from the lumen through diverticulum or mural defect. Considering clinical context is crucial in providing accurate diagnosis while preserving laboratory resources.