Structure
Each adrenal gland is a small, flattened, yellowish gland with a thick cortex around a thin reddish-brown medulla, and the two sides differ in shape.
- Right gland: pyramidal, sitting on the apex of the right kidney.
- Left gland: crescent-shaped, lying along the medial border of the left kidney from its upper pole down towards the hilum.
Both lie inside the renal (Gerota's) fascia with the kidney, but in their own compartment separated by a fascial septum and fat. This is why a kidney can be removed or can descend without taking the adrenal with it.
Cortex and medulla
The cortex develops from mesoderm and has three zones, from outside in.
| Zone | Main hormone | Control |
|---|---|---|
| Zona glomerulosa | Aldosterone (mineralocorticoid) | Renin and angiotensin, plasma potassium |
| Zona fasciculata | Cortisol (glucocorticoid) | ACTH |
| Zona reticularis | Adrenal androgens | ACTH |
The medulla develops from neural crest cells. Its chromaffin cells are modified postganglionic sympathetic neurons that release adrenaline and noradrenaline into the blood.
Relations
The right adrenal gland lies tucked behind the inferior vena cava and liver, while the left lies behind the stomach and pancreas; both rest posteriorly on the diaphragm.
| Relation | Right adrenal gland | Left adrenal gland |
|---|---|---|
| Anterior | Inferior vena cava medially; bare area of the liver laterally | Stomach across the lesser sac; body of pancreas and splenic artery |
| Posterior | Right crus of the diaphragm | Left crus of the diaphragm |
| Inferior | Upper pole of right kidney | Medial border of left kidney above the hilum |
| Medial | Right coeliac ganglion, right crus | Left coeliac ganglion, aorta |
Blood supply and innervation
Each adrenal gland is supplied by three groups of arteries but drained by a single vein from its hilum.
Arteries
- Superior suprarenal arteries: several small branches of the inferior phrenic artery.
- Middle suprarenal artery: a direct branch of the abdominal aorta at about L1.
- Inferior suprarenal artery: a branch of the renal artery.
These break into many small vessels that pierce the capsule, so the gland has a rich blood supply from all sides.
Veins
The right suprarenal vein is very short and enters the posterior surface of the inferior vena cava directly. The left suprarenal vein is longer and runs down to join the left renal vein, often together with the left inferior phrenic vein.
Lymph and nerves
Lymph drains to the lumbar (para-aortic) nodes. Nerves come from the coeliac plexus and the thoracic splanchnic nerves. Uniquely, the medulla receives preganglionic sympathetic fibres that synapse directly on the chromaffin cells, with no ganglion in between. The cortex has little functional innervation.
Clinical relevance
The venous anatomy and the deep position of the adrenals dominate their surgical and diagnostic importance.
- Right adrenalectomy: the short right suprarenal vein entering the IVC can tear and cause major haemorrhage, so it is controlled early.
- Left adrenalectomy: the left vein is found by tracing the upper border of the left renal vein.
- Adrenal vein sampling: used to lateralise primary aldosteronism; the right vein is harder to cannulate because it is short and enters the IVC directly.
- Functional tumours: an adrenocortical adenoma may cause Conn's syndrome (aldosterone) or Cushing's syndrome (cortisol); a phaeochromocytoma arises from the medulla and causes paroxysmal hypertension.
- Incidentaloma: adrenal masses are common incidental findings on abdominal CT.
- Waterhouse and Friderichsen syndrome: bilateral adrenal haemorrhage, classically in meningococcal septicaemia, causing acute adrenal failure.