Imaging features of radiation-induced changes in the abdomen.

After external-beam radiation therapy, radiation-induced changes may be observed in abdominal and pelvic organs at imaging. In the liver, an area of low attenuation corresponding to the radiation port (or an area of hyperattenuation if the underlying liver tissue shows fatty change) can be seen at computed tomography (CT) performed within 3-6 months after therapy. Later, the liver may be fibrotic and contracted. In the stomach, small intestine, and colon, wall thickening and edema are early manifestations. Ulcers may also be observed. Long-term complications include strictures and fistulas. After irradiation of the kidneys, altered attenuation of the renal parenchyma may be seen at CT. Ureteral strictures, typically involving the distal ureter, may be observed after pelvic irradiation. The bladder may be small and contracted with a thickened wall after radiation exposure. Fistulas between the bladder and other pelvic organs sometimes occur. Typical musculoskeletal changes include growth abnormalities in skeletally immature patients, fatty replacement of bone marrow, and radiation osteitis. Radiation-induced neoplasms are also recognized after therapy.