MR imaging of the adrenal gland: radiologic-pathologic correlation.

Abstract

Complex physiologic and neoplastic processes affect the adrenal glands. An appreciation of the gross pathologic and histologic correlates of disease aids in understanding the mechanisms by which diagnostic imaging helps characterize adrenal masses. Computed tomographic (CT) densitometry and chemical shift magnetic resonance (MR) imaging would seem to be the most reliable tools in determining whether a given adrenal mass is specifically an adenoma. Such a determination is made on the basis of the presence of substantial amounts of intracytoplasmic lipid. Thus, although a homogeneous mass with a CT attenuation of less than 10 HU or a decrease in signal intensity at opposed-phase MR imaging is diagnostic for adenoma, lesions that do not have these features are indeterminate and may necessitate biopsy. Adrenal myelolipoma also has a distinctive imaging appearance that reflects the presence of macroscopic fat deposits. Diagnosis of adenoma or adrenal myelolipoma is very helpful in the assessment and treatment of asymptomatic patients with adrenal masses and may make biopsy unnecessary. In patients with clinical or biochemical evidence of adrenal disease, MR imaging helps confirm the presence of a mass and allows localization and further characterization of the lesion.

Giant adrenal myelolipoma with minimal fat content in a patient with homozygous beta‐thalassemia: Appearance on MRI

“…These tumors, however, are usually catecholamine-secreting and therefore symptomatic, and do not demonstrate a drop in signal on opposed-phase images, like the tumor in our case. The hematopoietic element in myelolipomas usually has SI comparable to that of the spleen on T2-weighted images, and, to our knowledge, there are no reports of such tumors with very high SI (1,3,6,10). We hypothesize that the very high SI of the tumor on T2-weighted images in our case may be attributed to a combination of increased interstitial space and intense hemorrhagic infiltration, as was demonstrated on pathology.…”

“…The differential diagnosis of adrenal masses presenting with a drop in SI on opposedphase images without macroscopic fat includes adrenal adenoma and the rare adrenal cortical carcinoma. Adenomas usually have homogeneous SI and are hypointense to isointense on T2-weighted sequences, with uniform drop in SI on opposed-phase images, unlike the tumor in our case, which was large and inhomogeneous, with very high SI on T2-weighted images (3,8). The rare adrenal cortical carcinomas are large, lobulated tumors; they are frequently hormonally active, more common in female patients, and usually contain areas of necrosis and hemorrhage with inhomogeneous high SI on T2-weighted sequences.…”

“…The areas of drop in SI on the opposedphase images occupied the largest portion of the tumor. Extremely rarely, lipomas and liposarcomas originate in the adrenal glands (3), and diagnostic problems may arise in very large retroperitoneal tumors of uncertain origin (2). These tumors, however, usually contain abundant lipid content and macroscopic areas of fat.…”

“…The previously reported MRI findings include demonstration of macroscopic fatty elements, hemorrhagic components, and variable signal intensity (SI) on T2-weighted sequences, ranging from hypointensity to moderate hyperintensity (1)(2)(3). Coexistence of macroscopic fatty elements with areas of microscopic lipid, demonstrated by a drop in SI on opposed-phase images, has been reported (1).…”

Adrenal MRI: Techniques and clinical applications

“…3a,b). I suggest that to unequivocally establish the presence of macroscopic fat within an adrenal myelolipoma, one should compare an in-phase T1-weighted image with a corresponding fat-suppressed T1-weighted sequence (41)(42)(43). These techniques have Figure 1.…”