Pseudoinvasion in colon adenomas mimicking invasive carcinoma: diagnostic challenges and literature review

Relevance. Epithelial pseudoinvasion of colorectal adenoma is morphologically characterized by the detection of glands in the submucosa. The aim of the study was to increase awareness of submucosal pseudoinvasion for clinical purposes to prevent overly aggressive surgical treatment. Materials and methods. The surgical materials of 147 patients with polypoid and laterally spreading neoplasms of the colon were analyzed. Cases of pseudoinvasion in colon adenomas were described in detail. Results. Pseudoinvasion was detected in 3.4% (4/147) of cases. In 3 neoplasms, foci of severe dysplasia in the superficial sections were detected against the background of villous adenoma. In one case, a focus of epithelial prolapse was detected against the background of intramucosal carcinoma. Pseudoinvasion was detected in the muscularis mucosa and submucosal layer in the form of foci of a similar adenoma surrounded by fibrous stroma, the presence of extracellular mucus fields, elements of chronic inflammation with an admixture of segmented leukocytes, hemosiderin-rich macrophages, but without signs of stromal desmoplasia. Single glands were incomplete and uneven, with cytological signs of low-grade atypia. Unlike invasive carcinoma, tumor kidneys, lymphovascular and/or perineural invasion were not detected. In all cases of resection of colon neoplasms with pseudoinvasion, severe fibrosis of the submucosal layer was observed, which led to non-radical resection (the vertical resection margin passed along the prolapse focus – R1). Despite non-radical resections, no signs of relapse were obtained during control endoscopic examinations. At the stage of endoscopic dissection, foci of epithelial prolapse are difficult to differentiate from true tumor invasion, which may determine an unjustified transition to traditional surgical intervention. Conclusion. Pseudoinvasion in colon adenomas is a rare phenomenon. Endoscopic removal of such neoplasms is a difficult task due to severe fibrosis of the submucosal layer and is associated with a high probability of incomplete resection. However, the risks of recurrence after incomplete endoscopic resection are minimal.