The adrenal (suprarenal) glands (often shortened to just the adrenals) are paired organs of the endocrine system, often asymmetric in shape. 

Gross anatomy

The adrenal glands are located superior and anteromedial to the kidneys, within the perirenal space, and enclosed by perirenal fascia. Each has a body and two limbs: a medial and lateral limb. Coronally, the right adrenal gland is more pyramidal shaped, while the left more is more crescentic ⁷. Axially, the right adrenal gland is linear or V-shaped with larger medial limb and smaller lateral limb, while left adrenal gland is triangular shaped^1,11.

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. The cranio-caudal extent of the adrenal gland is less than 4 cm ¹¹. 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 fibrous capsule.

The cortex is subdivided into three zones (from outer to inner) ^5,7:

1. zona glomerulosa

2. zona fasciculata

3. zona reticularis

The medulla (chromaffin cells) produces catecholamines (adrenaline, noradrenaline) and dopamine.

Locations

The adrenal glands lie superior and anteromedial to the kidneys ¹. The left adrenal gland lies more anteromedial than superior when compared to the right adrenal gland ¹. The right adrenal gland lies in the angle between the right lobe of liver and crus of the right diaphragm, behind the inferior vena cava ¹. Meanwhile, the left adrenal gland lies posterolateral to the abdominal aorta ¹. The right adrenal gland is lower and more medial to the spine than the left adrenal gland ¹¹.

Relations

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

• lateral: spleen

• anterior: splenic artery, pancreas, stomach, lesser sac

• posterior: left kidney ^3,6,7

Arterial supply

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

• venous drainage ⁵

  • adrenal veins emerge from the hilum and drain to different veins depending on the side:

    • left adrenal vein drains to the left renal vein

      • may form a common trunk with the inferior phrenic vein before entering the left renal vein

    • right adrenal vein drains to the IVC

Lymphatic drainage

• lymphatics are contained within the capsule and drain to the para-aortic nodes ^7,9

Innervation

• presynaptic sympathetic fibres from thoracic splanchnic nerves synapse directly with chromaffin cells ⁹ 

• postsynaptic fibres from coeliac, aorticorenal, and renal ganglia innervate surrounding vessels

Variant anatomy

• 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

Radiographic features

Generally, the size of the adrenal gland should not be thicker than the adjacent crus of diaphragm ¹¹.

Ultrasound

• 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 visualise 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

CT 

Normal adrenal glands have similar density with liver and spleen on plain CT scan ¹².

The adrenal glands enhance after contrast administration to approximately 50-60 HU. Hyperenhancement of the adrenal gland is concerning for hypovolaemic shock.

MRI

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.

Development

Adrenal glands develop in the peritoneum and descend, in contrast to kidneys that develop in the pelvis and ascend. If the kidneys failed to develop, the adrenal glands are still found in their expected positions but their shape may be more discoid due to lack of moulding by the kidneys ¹¹.

At birth, the adrenal glands sizes are 1/3 of the kidneys. This gets smaller into adulthood where it becomes 1/13 of the kidneys in adults ¹¹.

Related pathology

• gamuts

  • adrenal calcification

  • adrenal congestion

  • adrenal hyperplasia

  • adrenal haemorrhage

• vascular

  • adrenal vein thrombosis

• traumatic

  • adrenal gland trauma

• neoplastic

  • tumours of the adrenal gland

• infections

  • adrenal tuberculosis

  • adrenal abscess

• inflammation

  • adrenalitis

• others

  • adrenal insufficiency