Adrenal (suprarenal) glands are part of both endocrine and nervous systems

Lie within perirenal space, bounded by perirenal (Gerota) fascia

Right adrenal is more apical in location

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  Lies anterolateral to right crus of diaphragm, medial to liver, posterior to inferior vena cava (IVC)

  
  
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  Often pyramidal in shape, inverted V shape on transverse section

Left adrenal is more caudal

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  Lies medial to upper pole of left kidney, lateral to left crus of diaphragm, posterior to splenic vein and pancreas

  
  
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  Often crescentic in shape, lambda, tricorn hat, or triangular on transverse section

Adrenal cortex

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  Derived from mesoderm

  
  
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  Has important endocrine functions

  
  
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  Secretes corticosteroids (cortisol, aldosterone) and androgens

Adrenal medulla

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  Derived from neural crest

  
  
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  Part of sympathetic nervous system

  
  
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  Chromaffin cells secrete catecholamines (mostly epinephrine) into bloodstream

Adrenal gland has very rich vascular and nervous connections

Arteries

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  Superior adrenal arteries : 6-8 from inferior phrenic arteries

  
  
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  Middle adrenal artery : 1 from abdominal aorta

  
  
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  Inferior adrenal artery : 1 from renal arteries

Veins

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  Right adrenal vein drains into IVC

  
  
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  Left adrenal vein drains into left renal vein (usually after joining left inferior phrenic vein)

Transducer: 2-5 MHz for adults

High-frequency (7.5- to 10.0-MHz) linear transducer used in neonates

Complex shape requires multiplanar evaluation

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  Sweeps should be taken in both transverse and longitudinal planes

Right adrenal gland

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  Intercostal transverse approach, using liver as acoustic window

  
  
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  Direct anterior abdomen scanning is limited by overlying bowel loops and depth to gland

Left adrenal gland

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  Intercostal at midaxillary line, using spleen or left kidney as acoustic window

  
  
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  In pediatric subjects and thin adults, direct transabdominal US at epigastrium

  
  
  
  
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    Stomach may be distended with fluid to serve as acoustic window

  
  

Sonographic appearance

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  Relative to body size, adrenal glands are much larger and more easily identified in neonatal population

  
  
  
  
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    Also makes them more vulnerable to hemorrhage

  
  
  
  
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  Cortex is hypoechoic with hyperechoic medulla

  
  
  
  
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    Creates ice cream sandwich appearance

  
  
  
  
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  Adrenal glands often difficult to see and easily overlooked in adult patients (especially if obese) unless specifically targeted

  
  
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  Any masses should be documented and measured

  
  
  
  
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    Pay particular attention to sonographic appearance (e.g., echogenic mass highly suggestive of fat in a myelolipoma)

  
  

Rich blood supply reflects important endocrine function

Adrenal glands are designed to respond to stress (trauma, sepsis, surgery, etc.) by secreting cortisol and epinephrine

Hemorrhage

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  Most common in neonatal population

  
  
  
  
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    Associated with many perinatal stressors: Asphyxia, sepsis, birth trauma, coagulopathies

    
    
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    Right > left; bilateral in 5-10%

  
  
  
  
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  Adults

  
  
  
  
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    Anticoagulation therapy most common cause

    
    
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    Overwhelming stress (surgery, sepsis, burns, hypotension) may result in adrenal hemorrhage, acute adrenal insufficiency (addisonian crisis)

    
    
    
    
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      Relatively uncommon condition but potentially catastrophic event

    
    
    
    
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    Blunt abdominal trauma

    
    
    
    
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      Generally unilateral (right > left)

    
    

  
  
  
  
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  Appearance changes over time

  
  
  
  
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    Acute: Hemorrhage appears echogenic & mass-like

    
    
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    Subacute: Blood products liquefy & contract, creating mixed echotexture mass

    
    
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    Chronic: Adrenal resumes normal size, ± Ca²⁺ or cyst

  
  

Metastases : Common site for hematologic metastases (lung, breast, melanoma, etc.)

Adrenal adenoma

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  Very common (at least 2% of general population), but most are small, nonfunctioning

  
  
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  Functional adenomas

  
  
  
  
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    Cushing syndrome (excess cortisol) : Truncal obesity, hirsutism, hypertension, abdominal striae

    
    
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    Conn syndrome (excess aldosterone) : Hypertension, hypokalemic alkalosis

  
  

Myelolipoma

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  Benign tumor composed of mature adipose tissue and variable amount of hematopoietic elements

  
  
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  Characteristic echogenic appearance on US

Pheochromocytoma

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  Catecholamine-secreting tumor from adrenal medulla

  
  
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  Location: Adrenal gland (90%), sympathetic chain from neck to bladder (10%)

Neuroblastoma

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  Most common extracranial solid malignancy in children (median age at diagnosis: 15-17 months)

  
  
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  Location: Adrenal gland > retroperitoneum > posterior mediastinum