Pathological characteristics of colorectal adenoma with submucosal pseudoinvasion

Objective: To investigate the pathomorphological characteristics of colorectal adenoma with submucosal pseudoinvasion and to summarize the corresponding pseudoinvasion patterns. Methods: The clinicopathological data of 9 cases of colorectal adenoma were collected at 989 Hospital of PLA Joint Logistics Support Force (4 cases) and Beijing Chaoyang Hospital, Capital Medical University (5 cases), from 2016 to 2019. retrospectively, and the histomorphological characteristics and immunophenotypes were analyzed, and discussed in light of the relevant literature. Results: There were 8 cases of adenoma with stalk. Tumor glands were found in the submucosa at the head end of adenoma, similar to infiltrating adenocarcinoma. The structure and cellular morphology of submucosal glands were very similar to the intramucosal tumor while the local submucosal tumor showed continuity with the intramucosal tumor. The submucosal tumors were lobule-like or nest-like with clear boundary. The outline of the gland was smooth and blunt-round, and there was loose fibromyxoid stroma around the gland, similar to the mucosa propria stroma. Some cases of the submucosal glands were cystic dilated with mucocele formation and hemosiderin deposition. One case with broad stalk-base showed an elevated adenoma with local high grade dysplasia involved in the aggregated lymphoid nodule, forming the lymphoglandular complexes, simulating invasive adenocarcinoma with associated submucosal lymphoid aggregates. Submucosal cancer tissue and intramucosal cancer tissue had continuity, and their morphology was the same. The submucosal tumor was round in the outline, smooth and blunt in the edge, and surrounded by lymphoid tissue. There was no stromal response around the gland to promote the proliferation of connective tissue, neither was there single-cell or small-cell cluster, sharp angle branch of gland, or vascular infiltration. Conclusions: There are two unique morphological patterns in colorectal adenoma with submucosal pseudoinvasion. Morphologically, the data show that one is lobular-like pattern, and the other is lymphoglandular complexes-like pattern. The main features of the two patterns are the same-morphology and continuity of submucosal tumor and intramucosal tumor. The pushed glands were surrounded by the intrinsic membrane stroma and muscularis mucosae in proper order, lacking the typical morphological characteristics of invasive adenocarcinoma.