Genitourinary Radiology > Adrenal Glands > Adenoma


Adenoma

Adrenal adenomas are common, benign tumors found in 1% of abdominal CT exams. Most are non-functional and incidental. However, functional adenomas may present as Cushing's syndrome, primary hyperaldosteronism, virilization, or feminization.

Increased intracellular lipid content leads to CT density of less than 10 Hounsfield units. They exhibit rapid contrast washout compared with metastases (the major differential consideration) and are usually less than 3 cm in diameter with well-defined and smooth contours. On MRI, we take advantage of the fact that adrenal adenomas have lipid in their cytoplasm. This lipid results in loss of signal on gradient echo T1 weighted MRI images lending the diagnosis of lipid rich adrenal adenoma.

Unenhanced CT scan through level of adrenals shows low density right adrenal mass.  Density was less than 10 HU (Hounsfield Units) consistent with a lipid rich adrenal adenoma.&

Adrenal protocol CT scan with (1) unenhanced, (2) enhanced and (3) 10 minute delayed images through left adrenal mass (arrow) in a patient with a lung malignancy.  Unenhanced scan shows left adrenal mass is > 10 Hounsfield units and therefore cannot be characterized as a lipid rich adrenal adenoma.  To take advantage of a second characteristic of adrenal adenomas, enhanced and delayed images were performed so we could evaluated the washout of contrast from the mass.  Adrenal adenomas will show > 50% washout while metastatic disease will not.  This sequences shows greater than 70% washout on the delayed images using the formula [(enhanced - delayed)/(enhanced-unenhanced)] X 100%.  These findings are consistent with adrenal adenoma based on washout characteristics.  Biopsy, therefore, is unnecessary.

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Another patient with a right adrenal mass on MRI (arrows).  T1 weighted coronal image shows intermediate signal mass.

T1 weighted gradient echo axial image shows mass is higher signal on in phase imaging.

T1 weighted gradient echo axial image shows mass drops in signal on opposed phase imaging.  This is diagnostic of adrenal adenoma.



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