Radiology and pathology of fat.

Conventional roentgenograms usually reveal a fatty tumor by its characteristic radiolucency. Exceptions to this presentation are the intrathoracic fatty tumors which are more often radiopaque than radiolucent. Obesity and steroids may cause focal, excessive accumulation of fat which can cause a mass effect and become symptomatic from pressure changes. Tubular widening of the superior mediastinum is characteristic mediastinal lipomatosis. Liposarcomas may or may not appear radiolucent. When a calcified retroperitoneal mass appears at least partially radiolucent, a liposarcoma must be suspected. Intrarenal fatty masses may be confused by overlapping bowel gas. Nephrotomograms, prior to the injection of contrast medium, will reveal the presence of fatty process. Obliteration of juxtavisceral or juxtamuscular fat is an important finding for localizing a disease process. CT is the most informative imaging method in establishing the presence of a fatty mass and for localizing a pathological process which infiltrates the juxtavisceral fat.