Pseudoinvasive squamous morula in a large colorectal polyp with low and high grade dysplasia

Abstract

Due to abdominal discomfort and a positive first-degree family history of bowel cancer, a woman (in her late 50s) underwent colonoscopy. A large (35 mm) colorectal adenoma of the ascending colon was removed by endoscopic mucosal resection. On histopathology, the adenoma showed low and focal high-grade dysplasia with nests of tumour cells with squamous differentiation and pseudoinvasion. The polyp was fully excised endoscopically; however, it needed complex polyps MDT discussion for an agreed follow up plan. Squamous morules, within colorectal adenomas, are rare benign lesions with low proliferative activity. Their incidence is reported to be around 0.4%. They can mimic malignant features and may be incorrectly diagnosed as invasive adenocarcinoma. While rare, they may be indicative of high risk of recurrence adenoma. We present this case as a satisfactory model of the advantages of precise diagnosis, clear explanation and discussion between experts, leading to an accurate follow-up plan.