Teaching Case

We report an incidental finding of an adrenal adenoma and we discuss the appearance on CT and MRI.

A 68 year old female with known diabetes mellitus and polyvascular diseases, presented refractory hypertension during the last 8 months. The Doppler ultrasonography was detecting bilateral renal artery stenosis. The CT evaluation -/+ contrast showed diffuse atheromatosis and confirmed the bilateral renal artery stenosis. An incidental right adrenal mass was detected. An MRI was performed.

Adrenal adenomas are the most common adrenal lesions, found in 3% of cases at autopsy. The adrenal adenoma may be nonhyperfunctioning or hyperfunctioning (Conn syndrome, Cushing syndrome, virilization or feminization). Adenomas have abundant intracytoplasmic fat in the adrenal cortex and thus have low attenuation at CT.
Although unenhanced CT has become the mainstay for characterizing lipid-rich adrenal adenomas, this imaging modality cannot help differentiate lipid-poor adenomas from nonadenomas. Several reports have demonstrated that delayed contrast material–enhanced CT or chemical shift magnetic resonance (MR) imaging are useful for the differentiation of lipid-poor adenomas (> 10 HU) and nonadenomas. Delayed enhanced CT can characterize additional hyperattenuating adrenal masses that cannot be characterized with chemical shift MR. Most adrenal adenomas demonstrate a loss of signal intensity on out-of-phase images. A decrease in signal intensity of more than 20% is considered diagnostic of an adenoma. Uniform enhancement on immediate contrast material–enhanced images is also typical of adenomas. Small, rounded foci of altered signal intensity may be seen within an adenoma owing to cystic changes, hemorrhage, or variation in vascularity. Rarely, adrenal adenomas may contain foci of hemorrhage. The main differential diagnosis is metastasis.