Tubular adenoma with squamoid morules in colonic polyp: Cases report and literature review.

Rationale: Squamoid morules (SM) are rare in colorectal adenomas. Submucosal pseudoinvasion in adenomas is similar to that in invasive carcinomas and needs to be differentiated, especially in the presence of mucin spillage.

Patient Concerns: We present 2 cases of adenomatous polyps associated with SM. One was approximately 3.2 × 1.8 cm-sized pedunculated polyp in the descending colon of a 57-year-old man, and the other was a 1 cm-sized fungating polyp in the ileocecal valve (ICV) of a 44-year-old man.

Diagnoses: The polyp of the descending colon was accompanied with a low-grade villotubular adenoma with submucosal pseudoinvasion, mucin spillage, and SM; the polyp of the ICV was accompanied with a low-grade tubular adenoma with SM; and transformation to a high-grade tubular adenoma was also observed.

Interventions: The polyps in the descending colon and ICV were removed using endoscopic mucosal resection hot-snare polypectomy and underwater endoscopic mucosal resection, respectively.

Outcomes: The lesions were completely removed, symptomatic improvement was achieved, and no relapse was observed.

Lessons: We encountered 2 cases of SM in adenomas of the colon, one of which was accompanied with submucosal pseudoinvasion and mucin spillage. This represents the 10th reported case of colorectal adenoma with submucosal pseudoinvasion and SM, and the first case report of mucin spillage in addition to submucosal pseudoinvasion and SM. SM are a very rare finding in adenomas and may be difficult to distinguish from malignant lesions with limited sampling, especially when submucosal pseudoinvasion and mucin spillage are additionally present. Available reports should be reviewed to examine the pathogenesis of SM and submucosal pseudoinvasion and to differentiate these from invasive cancer. This will aid in preventing misdiagnosis of invasive carcinoma when such findings occur in benign lesions.