Why can we not see a normal appendix on CT? An evaluation of the factors influencing nonvisualization of a normal appendix by 64-slice MDCT

PurposeThe aim of this study was to identify the factors that prevent the visualization of a normal appendix by 64-slice MDCT.Materials and methodsThirty-nine consecutive patients with a normal appendix not visualized during routine abdominal CT and without a history of abdominal surgery were selected for this study. In addition, 100 consecutive patients with a clearly visualized normal appendix by CT were selected as controls. Two radiologists, by consensus, evaluated MDCT images for cecum level, pericecal fat content, presence of small bowel dilatation, presence of pericecal fluid, presence of cecal wall thickening, and identification of the ileocecal valve.ResultsPatients with a nonvisualized normal appendix had a significantly lower cecum level, minimal pericecal fat, and a higher amount of pericecal fluid and were less likely to have an identified ileocecal valve (46.2%, 79.5%, 17.9%, and 76.9%, respectively) than patients with a clearly visualized appendix (18%, 9%, 4%, and 100%, respectively) (all P<.01). The presence of small bowel dilatation and cecal wall thickening was not statistically significant (7.7% vs. 8% and 7.7% vs. 9%, respectively) (all P>.01).ConclusionThe factors that influence the nonvisualization of a normal appendix on MDCT images are as follows: a low cecum level, minimal pericecal fat, presence of pericecal fluid, and nonidentification of the ileocecal valve.