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The adrenal (suprarenal) glands (often shortened to just the adrenals) are paired organs of the endocrine system, often asymmetric in shape.
Each gland is enclosed in the perirenal fascia and each has a body and two limbs: a medial limb and a lateral limb. However, the right adrenal gland is usually more pyramidal in shape while the left adrenal gland is more crescentic 7. On cross-section, right adrenal gland is linear, comma or V-shaped with larger medial limb and smaller lateral limb. While left adrenal gland is triangular or Y-shaped1,11.
The right adrenal gland has a maximum width of 6.1 mm and the left adrenal gland has a maximum width of 7.9 mm 6. Proportionately, the adrenal size is larger in neonates and infants, being almost one-third of the size of the kidney 2-4.
The adrenal gland consists of two portions: an outer cortex and an inner medulla. The outer cortex is derived by mesoderm while the inner medulla is derived from neural crest cells 11. The gland is covered by a collagenous capsule.
The cortex is subdivided into three zones (from outer to inner) 5,7:
- zona glomerulosa
- zona fasciculata
- zona reticularis
The medulla (chromaffin cells) produces catecholamines (epinephrine, norepinephrine) as well as dopamine.
The adrenal glands lie superior and anteromedial to the kidneys 1. The right adrenal gland is lower and more medial to the spine than the left adrenal gland 11.
Right adrenal gland
- medial: right crus of the diaphragm, right inferior phrenic artery
- lateral: right lobe (bare area) of the liver
- anterior: inferior vena cava (IVC)
- posterior: right kidney 3,6,7
Left adrenal gland
- medial: left crus of the diaphragm, left inferior phrenic artery
- anterior: lesser sac, stomach, splenic artery, pancreas
- lateral: spleen
- posterior: left kidney 3,6,7
The arterial supply is via three adrenal arteries 5:
superior adrenal artery which arises from the inferior phrenic artery
- usually a group of 6-8 arteries arise 10
middle adrenal artery which arises from the abdominal aorta
- often the largest of the adrenal arteries
- inferior adrenal artery which arises from the renal artery
- venous drainage 5
- lymphatics are contained within the capsule and drain to the para-aortic nodes 7,9
- presynaptic sympathetic fibers, from thoracic splanchnic nerves synapse directly with chromaffin cells 9
- post synaptic fibers from celiac, aorticorenal, and renal ganglia innervate surrounding vessels
lying down adrenal sign 8
- takes on a flattened appearance
- often in the presence of a pelvic kidney or renal agenesis
- adrenal gland hypoplasia or agenesis 8
- accessory adrenal rests
- often near adrenal glands but may be found anywhere in the abdomen, pelvis or scrotum 9
- horseshoe adrenal gland
Generally, the size of the adrenal gland should not be thicker than the adjacent crus of diaphragm 11.
- anterior transverse scanning is the best approach but the adrenal glands are often difficult to see 6:
- left adrenal gland seen ~40% at least once during scan
- right adrenal gland seen ~80% at least once during scan
- left adrenal gland is more difficult to visualize than the right because it is often posterior to the stomach and obscured by gas; this can be overcome by 6
- intercostal scanning in the posterior axillary line
- scanning through the spleen and left kidney with the left side of the patient elevated
The adrenal glands enhance after contrast administration to approximately 50-60 HU. Hyperenhancement of the adrenal gland is concerning for hypovolemic shock.
Adrenal glands are more easily seen on MRI than on CT because surrounding fat that give them contrast. Adrenal glands are isointense or hypointense when compared to liver on both T1-weighted and T2-weighted images. On fat suppression, the adrenal glands lose signals depending on cholesterol content on the adrenal cortex 11.
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