Adrenal gland

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

Gross anatomy

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. 

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 gland is covered by a collagenous 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 produces catecholamines (adrenaline, noradrenaline) as well as dopamine. 

Locations

The adrenal glands lie superior and anteromedial to the kidneys.

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
• anteromedial: diaphragm
• anterior: lesser sac, stomach, splenic artery, pancreas
• posterior: left kidney ^3,6,7

Blood supply

• arterial supply is via three adrenal arteries ⁵
  • superior adrenal artery (from inferior phrenic artery)
  • middle adrenal artery (from abdominal aorta)
  • inferior adrenal artery (from renal artery)
• 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
    • right adrenal gland drains to the IVC

Lymphatic drainage

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

Innervation

• splanchnic nerves via the aortic and renal plexuses ⁷

Variant anatomy

• lying down adrenal glandsign⁸
  • 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

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 and MRI

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

Right adrenal gland

• located superior and anteromedial to the upper pole of the right kidney
• appears as a linear, V-shape or comma-shape ¹

Left adrenal gland

• located superior and anteromedial to the upper pole of the left kidney
• appears as a triangular or Y-shape ¹

Related pathology

• adrenal gland trauma
• adrenal haemorrhage
• adrenal calcification
• tumours of the adrenal gland
• adrenal hyperplasia