الفهرس 
Introduction and Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
The adrenal gland is a frequent site of clinically silent mass. The incidental discovery of unsuspected adrenal mass has increased in past years, correlating to the increased use of body CT. The majority of inciden¬talomas are benign.(134) Although the possibility of malig¬nancy is small, the risk necessitates that each adrenal mass should be evaluated further. Biopsy can provide a defini¬tive diagnosis, but biopsy is somewhat invasive and is associated with a small but real risk of complication.(134) These circumstances have prompted the search for a noninvasive imaging procedure that can accurately characterize adrenal masses as either benign or malig¬nant. (134) MDCT has become the modality of choice in the identification and characterization of adrenal masses. (11,109,132) This utilization can be traced to two major developments. First, because MDCT is so frequently used in the diagnosis of abdominal symptoms and disorders, it has become the primary technique to cover unsus¬pected adrenal masses. (93) Secondly, MDCT has gained widespread acceptance as the technique of choice for differentiating adrenal adenomas (benign adrenal masses) from metastases. (109,132,93) The characterization of adrenal masses is accomplished by assessing their attenuation values and by evaluating the degree of iodinated contrast that has washed out of the mass upon delayed imaging. (11,133) Two traits of adenomas, one anatomic and one physiologic, have allowed CT to be used to differentiate adenomas from malignant lesions with a high degree of accuracy.(134) Adenomas typically demonstrate rapid washout, which is defined as an absolute percentage washout (APW) of more than 60% and a relative percentage washout (RPW) of more than 40% on delayed images. (99) Adrenocortical carcinoma typically has an RPW of less than 40%; however, large size and heterogeneity are more reliable indicators of the diagnosis than are washout values. Washout characteristics of pheochromocytoma are variable; in conjunction with high levels of dynamic enhancement, pheochromocytomas may mimic adenoma (ie, APW > 60%, RPW > 40%). (99) Myelolipomas appear as well-defined masses with variable quantities of fat and soft tissue. )99) After contrast material administration, metastases usually demonstrate slower washout on delayed images (APW < 60%, RPW < 40%) than do adenomas, although hypervascular metastases may enhance similarly to pheochromocytoma. Finally, a number of non adrenal pathologic conditions have been reported to mimic adrenal masses at CT.(99)