Differential diagnosis of fat-containing lesions with abdominal and pelvic CT.

Recognition of fat within an organ or lesion on abdominal and pelvic computed tomographic scans is an important clue to guiding a differential diagnosis. A systematic approach to these lesions, including a patient's age and clinical history, along with the appearance and location of the lesion often allows a specific differential diagnosis. The anatomic sites of origin for these lesions are the gastrointestinal tract, genitourinary system, and retroperitoneum. Some of the more common entities include various forms of fatty change in the liver, fibrofatty mesenteric proliferation in Crohn disease, ovarian dermoids, and herniations of abdominal fat. In addition, pitfalls such as pathologic processes engulfing normal fat (eg, perirenal abscess) and iatrogenic incorporation of normal fat (eg, omental packing in liver lacerations) should also be included in the differential diagnosis. Familiarity with certain benign occurrences, such as focal fat in the liver adjacent to the falciform ligament and lipomatous infiltration of the ileocecal valve, obviates invasive diagnostic procedures.