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.
Renal biopsy and radiologic follow-up were useful in identifying nonmalignant lesions in complex cystic renal masses and avoided unnecessary surgery in 39% of patients.
Deep pelvic abscesses may present a unique challenge for percutaneous drainage because of numerous overlying structures, which preclude safe percutaneous access. These structures include the pelvic bones, intestine, bladder, iliac vessels, and gynecologic organs. Use of the transgluteal approach to drain these abscesses can circumvent these obstacles and provide a useful surgical alternative or a temporizing measure. The transgluteal approach requires a thorough understanding of the anatomy of the sciatic foramen region and associated anatomic structures. The ideal approach for transgluteal access is to insert the catheter as close to the sacrum as possible, at the level of the sacrospinous ligament. Transgluteal drainage can be performed with the tandem-trocar technique or the Seldinger technique. Modifications of the procedure are needle aspiration not followed by catheter placement, use of the angled gantry technique, bilateral transgluteal drainage, combined anterior and posterior drainage, and drainage of necrotic pelvic masses. The transgluteal approach is a useful option in pediatric patients. Daily catheter care is essential for successful percutaneous catheter therapy. Although pain has been cited as a common complication of the technique, this complication can be minimized with judicious use of analgesia and a meticulous technique. Other complications are hemorrhage and catheter malposition.
Although certain multidetector CT findings are very specific for the diagnosis of perforated appendicitis, overall multidetector CT sensitivity is poor. Unless abscess or extraluminal gas is present, multidetector CT cannot enable the diagnosis of perforation.
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