adrenal adenomas are rich in lipids leading to low attenuation on noncontrast CT.An attenuation value of less than 10 Hounseld units on noncontrast CT has demon­strated a sensitivity of 71% and specicity of 98% for diagnosis of an adenoma [68]. Those that are lipid poor (and which therefore do not have low attenuation on non­contrast CT) can be investigated with contrast-enhanced CT using venous (60–75s) and delayed (15min) scans, although protocols vary by institution [69]. Because of their rich vascularity, adrenal adenomas demonstrate rapid washin and rapid wash­out of contrast material, compared with non-adenomatous lesions which tend to wash out more slowly [67]. The diagnosis of adrenal adenomas on MRI is based on the “chemical shift” phenomenon. Because of slight differences in the magnetic resonant frequencies of water and fat molecules, lipid-rich adenomas demonstrate decreased signal intensity on out-of-phase MRI sequences [69]. Notably, the major­ity of adrenal adenomas are nonfunctioning. The distinction between functioning and nonfunctioning lesions cannot be made on imaging ndings alone and may necessitate adrenal venous sampling [70]. In patients with primary pigmented nodu­lar adrenal disease, the adrenal glands typically show multiple small nodules with interposed atrophy of the adrenal cortex, although ndings can also be normal on CT.In macronodular adrenal hyperplasia, the glands appear massively enlarged and distorted with multiple nodules of varying sizes (Fig.4.7) [71].