Gastrointestinal: Obscuration of anorectal lesions in computed tomographic colonography due to balloon deflation.

Abstract

An asymptomatic 58-year-old man underwent computed tomographic colonography (CTC) performed using a thin catheter (4.7-mm diameter) and automated carbon dioxide insufflation. The procedure was performed in the supine and prone positions with inflated and deflated balloons, respectively. An experienced physician detected a polyp in the supine images (Fig. 1a,b), but not in the prone position images(Fig. 1d,e). Colonoscopy revealed a fibroepithelial polyp (11 mm; hypertrophied anal papillae; Fig. 1c), which was concealed in the anal canal upon air aspiration (Fig. 1f). A 79-year-old woman who was diagnosed with lower rectal cancer by colonoscopy underwent a preoperative CTC evaluation (submucosal well-differentiated adenocarcinoma, Fig. 2a,b). The catheter and the dilatation method were the same as in the first case. Flat lesions were visible in the supine position with the inflated balloon (Fig. 2c,d), but not in the prone position with the deflated balloon (Fig. 2e,f). The catheter accidentally withdrew from the anus in this second case. A radiologist faces many pitfalls during CTC interpretations of anorectal lesions. One of these is that lesions are occasionally obscured by the inflated rectal balloon catheter. Hence, balloon deflation in the prone position is recommended while obtaining images. Despite this, the diagnosis of anorectal lesions is difficult. A combination of CTC and sigmoidoscopy is not recommended by any guidelines, as there are few additional lesions found. Although the rectum is more distended in the prone position, balloon deflation can reduce rectal distension. Consequently, the lesion can be concealed in the anal canal and obscured in the CTC image, as in the present cases. This could be due to gas leakage from the anal canal and the absence of physical expansion of the balloon. However, upon initial inspection, the dilatation appeared successful as the rectum did not entirely collapse. However, the fact that lesions can be obscured by balloon deflation has never been reported. We believe that this original report would be instructive to radiologists and physicians. Physicians interpreting CTCs should be aware that both inflated and deflated balloons can obscure lesions.