[Appendiceal diverticulosis, a potential mimic of low grade appendiceal mucinous neoplasm: analysis of 20 cases]

Objective: To study the clinicopathologic features and the key points of differential diagnosis of appendiceal diverticulosis (AD) and low-grade mucinous neoplasm (LAMN) to avoid over-diagnosis. Methods: The clinical data, pathologic features and follow-up information of 20 patients with AD, who were diagnosed in the Peking University Third Hospital from January 2010 to November 2019 were collected and compared with 44 cases of LAMN which were diagnosed during the same period. Results: Among the 20 cases of AD, hypermucinous epithelium, filiform villi or undulating epithelium and mucosa atrophy were observed in 10 (50.0%), 4 (20.0%) and 14 (70.0%) cases, respectively, however, focally loss of lamina propria and mucosa/submucosa fibrosis were observed only in 1 (5.0%) and 4 (20.0%) cases, respectively. Extramural mucin deposits were seen in 11 (55.0%) cases, all were acellular mucin. Mucosal Schwann cell hyperplasia were present in 12 (60.0%) cases. Nine (45.0%) and 5 (25.0%) cases were associated with acute diverticulitis or acute suppurative appendicitis, respectively. In comparison with AD, LAMN cases more frequently showed hypermucinous epithelium (42/44, 95.5%), filiform villi or undulating epithelium (43/44, 97.7%), loss of lamina propria (43/44, 97.7%) and fibrosis and hyalinization of appendiceal wall (44/44, 100.0%), whereas mucosal atrophy (4/44, 9.1%) and Schwann cell hyperplasia(11/44, 25.0%) were less frequently seen (P<0.05). Follow-up information was available for 10 AD patients and 27 LAMN patients; all were alive without evidence of recurrence. Conclusions: Epithelial hyperplasia, loss of lamina propria, fibrosis of the appendiceal wall and extramural mucin deposits may occur focally in AD and should be distinguished from LAMN. The preservation of normal appendiceal mucosa architecture, lack of diffuse appendiceal wall fibrosis and hyalinization, and no definite neoplastic epithelium are the key point for preventing over-diagnosis.