Yiyan Lu1,2, Changhai Qi2, Hongbin Xu3, Mulan Jin4. 1. Department of Pathology, Beijing Chao-Yang Hospital, Capital Medical University, No.8 Gongren Tiyuchang South Road, Chaoyang District, Beijing, 100020, China. 2. Department of Pathology, Aerospace Center Hospital, Beijing, China. 3. Department of Myxoma, Aerospace Center Hospital, Beijing, China. 4. Department of Pathology, Beijing Chao-Yang Hospital, Capital Medical University, No.8 Gongren Tiyuchang South Road, Chaoyang District, Beijing, 100020, China. kinmokuran@163.com.
Abstract
PURPOSE: To identify clinicopathological features for the differential diagnosis of appendiceal serrated lesions and polyps (SPs) and low-grade appendiceal mucinous neoplasm (LAMN) for the purpose of avoiding over-diagnosis. METHODS: Clinical data and pathological features of 66 patients with SPs diagnosed at the Aerospace Center Hospital between January 2013 and January 2021 were collected and compared to 22 cases of LAMN. RESULTS: SPs, compared with LAMN, are likely to be associated with acute inflammation (SPs 53.0% vs. LAMN 18.2%), and may be located in the appendix partly, although with smaller diameter (average 9.6 vs. 27.2 mm); epithelial structures of serrated (100% vs. 22.7%) and filiform villous (47.0% vs. 18.2%) were often found in SPs. SPs occasionally show attenuated or flattened morphology (16.7% vs. 100%) and undulating or scalloped (7.6% vs. 40.9%) structures, and can also be accompanied by diverticulum (18.2% vs. 18.2%) and acellular mucin in the appendiceal wall (16.7% vs. 54.5%), which causes confusion with LAMN. The key point of the differential diagnosis is to observe whether the muscularis mucosa exists (loss, 0% vs. 100%) and fibrosis of the appendiceal wall (0% vs. 100%). SMA immunohistochemistry can assist in the diagnosis. Calcification is also indicative of LAMN. CONCLUSIONS: The epithelial structure of SPs can appear flattened and focally scalloped, and can be accompanied by mucin in the appendiceal wall, which may appear as complex lesions, easily over-diagnosed as LAMN. Key differential diagnostic features are identifying the structure of lamina propria, determining whether the muscularis mucosa exists, and whether the appendiceal wall is fibrotic.
PURPOSE: To identify clinicopathological features for the differential diagnosis of appendiceal serrated lesions and polyps (SPs) and low-grade appendiceal mucinous neoplasm (LAMN) for the purpose of avoiding over-diagnosis. METHODS: Clinical data and pathological features of 66 patients with SPs diagnosed at the Aerospace Center Hospital between January 2013 and January 2021 were collected and compared to 22 cases of LAMN. RESULTS: SPs, compared with LAMN, are likely to be associated with acute inflammation (SPs 53.0% vs. LAMN 18.2%), and may be located in the appendix partly, although with smaller diameter (average 9.6 vs. 27.2 mm); epithelial structures of serrated (100% vs. 22.7%) and filiform villous (47.0% vs. 18.2%) were often found in SPs. SPs occasionally show attenuated or flattened morphology (16.7% vs. 100%) and undulating or scalloped (7.6% vs. 40.9%) structures, and can also be accompanied by diverticulum (18.2% vs. 18.2%) and acellular mucin in the appendiceal wall (16.7% vs. 54.5%), which causes confusion with LAMN. The key point of the differential diagnosis is to observe whether the muscularis mucosa exists (loss, 0% vs. 100%) and fibrosis of the appendiceal wall (0% vs. 100%). SMA immunohistochemistry can assist in the diagnosis. Calcification is also indicative of LAMN. CONCLUSIONS: The epithelial structure of SPs can appear flattened and focally scalloped, and can be accompanied by mucin in the appendiceal wall, which may appear as complex lesions, easily over-diagnosed as LAMN. Key differential diagnostic features are identifying the structure of lamina propria, determining whether the muscularis mucosa exists, and whether the appendiceal wall is fibrotic.
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