Colonic Endometriosis with Extensive Smooth Muscle Metaplasia Simulating Leiomyoma

Abstract

It is difficult to distinguish colonic endometriosis with smooth muscle metaplasia from a colonic neoplasm. Especially, in a small biopsy specimen, marked smooth muscle proliferation can be misdiagnosed as a spindle cell lesion such as leiomyoma or as a gastrointestinal stromal tumor. We present the case of a woman aged 48 years who had a colonic polyp, raising suspicion of a submucosal tumor. In a endoscopic polypectomy specimen, the lesion showed marked smooth muscle proliferation but in the resection specimen, a nodular mass, composed of endometrial glands, stroma, and a smooth muscle component, was identified. By immunohistochemical staining, smooth muscle cells were positive for estrogen receptor, progesterone receptor, smooth muscle actin, and smooth muscle myosin heavy chain. Endometriosis in the colon can be misinterpreted as a benign or malignant neoplasm. When examining small biopsy specimens, clinicians and pathologists should be aware of the potential of this condition to mimic other intestinal diseases.