Endometriosis in the cecum diagnosed via forward-viewing endoscopic ultrasound-guided tissue acquisition with a 19G fine-needle biopsy needle: a case report.

Subepithelial lesions (SELs) in the lower gastrointestinal tract are rare, and diagnosis and treatment of colorectal SELs are often challenging. Although endoscopic ultrasound-guided tissue acquisition (EUS-TA) is useful for minimally invasive histological diagnosis, few reports have described its use for right-sided colonic SELs because advancing an oblique-viewing echoendoscope into the right colon is difficult. A 30-year-old woman was referred to our hospital after colonoscopy revealed a protruding cecal lesion suggestive of an SEL. Contrast-enhanced computed tomography showed a 37-mm contrast-enhancing mass and an adjacent lesion, thought to be an enlarged lymph node, and gastrointestinal stromal tumor was suspected. A forward-viewing echoendoscope was inserted transanally and advanced successfully to the cecum in 4 min. EUS-TA of the cecal mass was performed using a 19-gauge fine-needle biopsy needle, and EUS-TA of the adjacent lesion was performed using a 25-gauge fine-needle biopsy needle. Histopathological and immunohistochemical examinations showed endometrial glands and stroma with positivity for estrogen receptor, progesterone receptor, and CD10, leading to a definitive diagnosis of endometriosis. This diagnosis enabled initial non-surgical management without immediate surgery.