adrenal gland

The adrenal (suprarenal) glands (often shortened to just the adrenals) 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 .

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 . Proportionately, the adrenal size is larger in neonates and infants, being almost one-third of the size of the kidney .

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) :

  • zona glomerulosa
  • zona fasciculata
  • zona reticularis
  • The medulla (chromaffin cells) produces catecholamines (epinephrine, norepinephrine) as well as dopamine.

    Locations

    The adrenal glands lie superior and anteromedial to the kidneys.

    Relations
    Right adrenal gland
    Left adrenal gland

    Arterial supply

    Venous drainage

    • venous drainage
      • 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 join with the left inferior phrenic vein before entering 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

    Innervation

    • presynaptic sympathetic fibers, from thoracic splanchnic nerves synapse directly with chromaffin cells  
    • post synaptic fibers from celiac, aorticorenal, and renal ganglia innervate surrounding vessels

    Variant anatomy

    • lying down adrenal sign 
      • takes on a flattened appearance
      • often in the presence of a pelvic kidney or renal agenesis
    • adrenal gland hypoplasia or agenesis
    • accessory adrenal rests
      • often near adrenal glands but may be found anywhere in the abdomen, pelvis or scrotum
    • horseshoe adrenal gland

    Radiographic features

    Ultrasound
    • anterior transverse scanning is the best approach but the adrenal glands are often difficult to see :
      • 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
      • 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 hypovolemic 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
    Left adrenal gland
    • located superior and anteromedial to the upper pole of the left kidney
    • appears as a triangular or Y-shape

    Related pathology