CT and MRI of the Adrenal Glands

1

What are common indications for computed tomography (CT) and magnetic resonance imaging (MRI) of the adrenal glands?

The most common clinical indications include:

• Characterization of indeterminate adrenal lesions incidentally detected on prior cross-sectional imaging. The main goal in this situation is to determine whether an adrenal lesion represents a benign lesion, such as an adenoma, or a malignant lesion.

• Detection and characterization of culprit adrenal lesions in patients with symptoms or signs suggestive of an endocrine disorder such as hyperaldosteronism, hypercortisolism, or increased catecholamine secretion.

• Staging and response assessment of patients with primary adrenal malignancies.

• Staging and response assessment of patients with extraadrenal malignancies that may metastasize to the adrenal glands.

• Providing guidance for percutaneous biopsy or intervention for an adrenal lesion.

2

What is the normal appearance of the adrenal glands on CT and MRI?

The adrenal glands are anterosuperior to the upper poles of the kidneys and are located within the perinephric space of the retroperitoneum. The right adrenal gland is located anterior and lateral to the right diaphragmatic crus, posterior to the inferior vena cava, and medial to the right hepatic lobe. The left adrenal gland is located anterior and lateral to the left diaphragmatic crus, posterior to the splenic vessels at the level of the pancreas or stomach, and medial to the spleen.

On CT, the adrenal glands have soft tissue attenuation, and on MRI, they have intermediate T1-weighted and slightly high T2-weighted signal intensity relative to skeletal muscle. Each adrenal gland is comprised of a body, a medial limb, and a lateral limb and often has an inverted letter “Y” or “V” configuration. Each adrenal gland limb is usually ≤ 6 mm in thickness ( Figure 36-1 ). However, the left adrenal gland is generally thicker and more nodular than the right adrenal gland, and the adrenal glands often increase in thickness/volume and become more nodular with increasing age.

The adrenal glands typically receive arterial blood supply from three separate arteries, although variations can occur: the superior adrenal arteries arise from the inferior phrenic arteries; the middle adrenal arteries arise from the lateral aspect of the abdominal aorta; and the inferior adrenal arteries arise from the superior aspect of the renal arteries. The right adrenal vein drains into the inferior vena cava, whereas the left adrenal vein joins with the left inferior phrenic vein before draining into the left renal vein, although variants are common.

Unenhanced CT images (but not MR images) are useful to detect adrenal calcifications. Unenhanced images on both CT and MRI are useful to (1) detect presence of macroscopic fat within an adrenal nodule to establish a specific diagnosis of adrenal myelolipoma, (2) detect presence of microscopic lipid content within an adrenal nodule to establish a specific diagnosis of adrenal adenoma, and (3) serve as a reference of comparison for contrast-enhanced images for adrenal nodule characterization.

3

What is a pancake adrenal gland?

A pancake adrenal gland is a congenital anomaly of the adrenal gland which may be seen when there is ipsilateral renal agenesis or renal ectopia. On cross-sectional imaging, the adrenal gland will appear to have a discoid or flattened configuration, and the ipsilateral kidney will not be visualized in its expected location ( Figure 36-2 ).

4

What is the significance of hyperenhancement of the adrenal glands?

Adrenal gland hyperenhancement (i.e., adrenal gland enhancement similar to that of adjacent vascular structures) is a finding that may indicate presence of shock or impending shock and tends to portend a poor clinical outcome. This may occur in the setting of trauma, pancreatitis, sepsis, or hemorrhage-induced hypotension.

5

What are the major causes of adrenal gland calcification?

• Prior adrenal gland infection such as tuberculosis or histoplasmosis.

• Prior adrenal gland hemorrhage.

• Adrenal gland neoplasm such as adrenal myelolipoma or adrenal cortical carcinoma (ACC).

6

How often are incidental adrenal lesions detected on cross-sectional imaging?

Adrenal incidentalomas are encountered in up to 7% of cross-sectional imaging studies and increase in prevalence with increasing age. Fifty percent to 80% of adrenal incidentalomas are secondary to nonhyperfunctioning adrenal adenomas (the most common cause), 5% to 10% are secondary to adrenal myelolipomas (the second most common cause), and up to 5% are secondary to adrenal pheochromocytoma (the third most common cause). In patients without a history of cancer, adrenal incidentalomas are rarely malignant in etiology. However, in patients with a history of cancer, up to 50% of incidentally detected adrenal lesions are malignant in nature, most often secondary to metastatic disease.

7

What is the major differential diagnosis for a focal adrenal gland lesion?

For the answer, see Box 36-1 .