Small bowel CT fat density target sign in chronic radiation enteritis.

On CT, a thickened intestinal wall configured with a middle layer of low attenuation surrounded on each side by layers of higher attenuation has been termed the target sign. The presence of fat within the submucosal layer of the small intestine is a well-known manifestation of Crohn's disease, but has not been reported in other chronic intestinal diseases. We describe CT findings of fat density target sign in a patient with prior radiation.

Bowel wall fat halo sign in patients without intestinal disease.

OBJECTIVE: 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. MATERIALS AND METHODS: 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. RESULTS: 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). CONCLUSION: 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.

Algorithmic approach to CT diagnosis of the abnormal bowel wall.

Computed tomography demonstrates intestinal wall abnormalities that can be analyzed by categorizing attenuation changes in the intestinal wall and transposing morphologic characteristics learned from barium studies. These attenuation patterns include white, gray, water halo sign, fat halo sign, and black. The white pattern represents avid contrast material enhancement that uniformly affects most of the thickened bowel wall. If the bowel wall is enhanced to a degree equal to or greater than that of venous opacification in the same scan, it should be classified in the white attenuation pattern. Common diagnoses with this pattern include idiopathic inflammatory bowel diseases and vascular disorders. The gray pattern is defined as a thickened bowel wall with limited enhancement whose homogeneous attenuation is comparable with that of enhanced muscle. This pattern is used to differentiate between benign and malignant disease, but it is the least specific of the patterns and should be combined with morphologic observations. The water halo sign indicates stratification within a thickened bowel wall that consists of either two or three continuous, symmetrically thickened layers. Common diagnoses with this sign include idiopathic inflammatory bowel diseases, vascular disorders, infectious diseases, and radiation damage. The fat halo sign refers to a three-layered target sign of thickened bowel in which the middle or "submucosal" layer has a fatty attenuation. Common diagnoses with this sign include Crohn disease in the small intestine and idiopathic inflammatory bowel diseases in the colon. Black attenuation is the equivalent of pneumatosis, and this pattern is commonly seen in ischemia, infection, and trauma.

Right-sided colonic diverticulitis: CT findings.

Right-sided colonic diverticulitis is an uncommon but clinically significant condition as it closely mimics other common acute right-sided abdominal conditions like acute appendicitis and cholecystitis. CT can provide a rapid and accurate diagnosis of this condition and thereby prevent unnecessary laparotomy and surgical procedures since it is essentially a benign self-limiting condition requiring medical treatment. It is the aim of this pictorial essay to describe the CT findings and increase awareness among radiologists of this condition.