Bowel Wall Fat Halo Sign in Patients Without Intestinal Disease

Stratification with a fat layer in the intestinal wall is thought to be a reliable marker for inflammatory bowel disease. We evaluated the presence and frequency of the bowel wall fat halo sign in patients undergoing abdominal CT for clinical indications unrelated to the gastrointestinal tract. We performed a retrospective review of 100 consecutive abdominal and pelvic CT examinations in 61 men and 39 women (mean age, 56 years) with clinical suspicion of renal stone disease. Two radiologists experienced in abdominal imaging performed qualitative and quantifiable assessment of the images. Five segments of the colon (ascending colon, transverse colon, descending colon, sigmoid colon, and rectum) and the terminal ileum (for approximately 1 ft [30 cm]) were evaluated for the presence of the fat halo sign. If the fat halo sign was present, fat density and total wall-thickness assessments were made. Presence or absence of clinical and radiologic signs of inflammatory bowel disease was determined. The Student's t test was used to evaluate the statistical significance, correlating body weight and presence of the halo sign. The fat halo sign was seen in 21 (21%) of 100 patients. Of the 21 patients with the fat halo sign, six (29%) had renal stone disease and 15 (71%) had no stone disease. The density value of the halo sign ranged from -18 to -64 H (mean, -41 H). The distribution of the fat halo sign was as follows: the terminal ileum, 4%; the ascending colon, 28%; the transverse colon, 34%; the descending colon, 36%; the sigmoid colon, 14%; and rectum, 10%. No patient with this sign had any remote, recent, or subsequently recorded history of inflammatory bowel disease. A statistically significant relationship (p < 0.001) was seen between the presence of the fat halo sign and body weight distribution, with 16 of 21 patients weighing over 200 lb (90 kg). In the absence of clinical or radiologic evidence of inflammatory bowel disease, the presence of the fat halo sign may represent a normal finding that is possibly related to obesity.