A Rare Subepithelial Lesion of the Proximal Colon Evaluated Using Miniprobe Endoscopic Ultrasonography: A Case Report

Preoperative diagnosis of submucosal lesions in the colon can be challenging. Total colonoscopy comprising miniprobe endoscopic ultrasonography (mEUS) revealed a 5-mm submucosal lesion in the transverse colon as a hypoechoic area primarily within the submucosa in our patient. However, a definitive diagnosis could not be made after evaluating the biopsy results. Based on the mEUS findings, adhesion to the muscularis was localized; therefore, endoscopic submucosal dissection was performed. A postoperative pathology examination revealed a parasite-like structure at the center of the necrotic tissue that was diagnosed as a colorectal-type necrotic nodule. Diagnostic EUS should be considered for such cases, and mEUS is useful for assessing the safety of specimen collection. This technique is especially valuable for diagnosing colorectal submucosal lesions in the proximal colon, where other diagnostic modalities are limited, and may contribute to safer endoscopic mucosal resection and endoscopic submucosal dissection.