Malignant Rectal Polyp Overlooked on CT Colonography Because of Retention Balloon: Opposing Crescent Appearance as Sign of Compressed Polyp

Abstract

WEB This is a Web exclusive article. bscuration of rectal lesions by a rectal catheter or by its retention balloon is a well-established diagnostic pitfall at barium enema examination that often requires deflation of the balloon or removal of the catheter to obtain an unobscured view [1]. Rectal lesions missed at CT colonography (CTC), on the other hand, are rare because of the relatively small size of the rectal catheter, the proclivity of the rectum for adequate luminal distention, and the fact that a retention balloon is not needed in most patients [2]. Although a retention balloon is not necessarily required for CTC, it may be helpful for optimal colonic distention in a select group of patients with insufficient anal sphincteric tone. Its use, however, may pose another potential source of false-negative results. A distended retention balloon may compress a rectal polyp against the wall of the rectum, thereby altering the gross morphology of the lesion and allowing the polyp to escape detection on CTC review. To our knowledge, the occurrence of a rectal polyp being compressed by a retention balloon or of a rectal polyp being compressed to the degree that was seen in our patient has not been reported. We report a case whereby a 12mm polypoid rectal adenocarcinoma arising in a tubular adenoma was missed both prospectively and retrospectively at CTC performed using an inflated retention balloon. We also suggest a finding at CTC that may help correctly identify a retention balloon–induced compressed polyp.