Adrenal adenoma

most common adrenal tumor and may occur in up to 9% of patients (post mortum data)
increased incidence in patients with diabetes or hypertension
most adenomas have a high proportion of intracellular lipid and so are of low CT attenuation
up to 30% of adenomas do not contain intracellular lipid
normal adrenal cortex secretes cortisol, aldosterone, and androgens
normal adrenal medulla secretes epinephrine and norepinephrine
most adrenal adenomas are normally functioning glands although adenomas can be a cause of adrenal hyperfunction
15-25% of cases of Cushing’s syndrome are due to adrenal masses, most commonly adenomas
adrenal adenomas account for up to 80% of cases of primary aldosteronism. These lesions are small with over 20% being less than 1 cm in size
up to 10% of cases bilateral
CT is now the study of choice to diagnosis an incidental adrenal adenoma

on noncontrast CT adenomas are typically of low CT attenuation (<10HU) and are easily recognized
usually 2-4 cm in size and usually round or oval in shape
following infusion of iodinated contrast adenomas may enhance but will de-enhance relatively quickly.
washout of an adenoma at 10 minutes post injection is over 50% and is diagnostic of a adenoma and no follow-up necessary
calcification is rare
lipid poor adenomas (noncontrast value of >10HU) have a washout pattern similar to lipid rich adenomas

signal typically low on T2 weighted images
chemical shift imaging can be done to identify fat within the lesion as signal intensity is decreased relative to normal tissue

preliminary reports show that malignant masses have increased FDG uptake while adenomas have no increased uptake

CT is the study of choice and if an adenoma is considered non-contrast scans are usually suffiecient (attenuation value <10 HU). If IV contrast is given (typical incidental finding) and lesion is less than 37 HU at 15 minutes psot injection it is still considered benign. If it is denser than 37 HU then delayed scans are done to look for washout. Using a washout value of 40% results in a sensitivity of 96% and a specificity of near 100% for diagnosis of an adenoma.
CT scanning of the adrenal gland is done with 3 mm thick sections at 3 mm intervals (or less)

most adrenal adenomas are detected as incidental findings on CT or MR scans
adrenal adenomas can be hyperfunctioning and are detected as part of a workup for Cushings syndrome, primary aldosteronism and Conn syndrome

adrenal adenomas tend to remain stable is size and once diagnosed no follow up is necessary
adrenal adenomas have no increased malignant potential treatment
when imaging is unsuccessful a biopsy can be done which has low complication rate and a high degree of accuracy (up to 96% in one series)
if an adenoma is diagnosed by CT (based on noncontrast or contrast CT with washout( then no follow up is necessary
if adenoma is hyperfunctioning it is removed via laprascopic procedure

Imaging of Adrenal Incidentalomas: Current Status
Dunnick NR, Korobkin M
AJR 2002;179:559-568
Spectrum of CT Findings in nonmalignant disease of the adrenal gland
Kawashima A, Sandler CM , Fishman EK et al.
RadioGraphics 1998;18:393-412
CT Time attenuation curves of adrenal adenomas and nonadenomas
Korobkin M, Brodeur FJ, Francis IR et al.
AJR 1998;170:747-752