This imaging methodology quantitates loss of contrast enhancement by a lesion and thus informs of lipid content in a given mass. Instead, the vast majority of these lipid-poor adenomas can be characterized employing a CT washout study. Nevertheless, 30% of adrenal adenomas are lipid-poor, also termed “atypical” by some authors, and cannot be differentiated from non- adenomas on non-contrast CT nor MRI. 1 It is important to understand that non-contrast CT and MR imaging (MRI) are largely equally informative with regard to assessment of intracellular lipid. 10,11 Macroscopic lipid is diagnostic of myelolipoma. Similarly, opposed phase chemical-shift MR imaging, as qualified by signal drop out, can prove the presence of intra- cellular lipid and thus confirm the presence of adrenal adenoma. 8 As such, low attenuation (less than 10 HU) on non-contrast CT scan is diagnostic for adrenal adenoma. Whether employing magnetic resonance (MR) or computed tomography (CT), assessment of intracytoplasmic lipid content forms the basis of adrenal imaging, since high cellular lipid is pathognomonic for adrenal adenoma-the most common adrenal lesion. 7 As such, adrenals are best visualized with cross-sectional imaging studies. Ultrasound provides inadequate visualization of adrenal pathology, especially of the left adrenal gland.
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