Adrenal Nests And Embryology Of Adrenal Gland

Adrenal nest is the presence of a collection of adrenal tissue, away from the adrenal gland due to migration of adrenal cortical tissue along with gonads 

Also known as accessory adrenal tissue 

Both the adrenal gland and gonads are developed from the urogenital ridge.

Therefore in some occasions, during embryogenesis adrenal cortical tissue can migrate along with gonads during its’ decent to the scrotum.


Composition Of Adrenal Nests

  • Usually composed on only adrenal cortical tissue
  • Rarely can present with adrenal medullary cells 


Locations Of Adrenal Nests

  • Common locations
    • Broad ligament
    • Spermatic cord
    • Hilum of ovary or testes
  • Rare locations
    • Retroperitoneal space along urogenital ridge
    • Renal capsule
    • Hepatic capsule
    • Intracranial cavity


Incidence

  • 50% of neonates at birth
  • It gradually regress over time and in adulthood adrenal nest are present in about 1% of the population 
 
There can be underlying malformations, therefore always have to investigate to exclude any of such associations
 
For proper understanding of adrenal nests, it is necessary to know the development of the adrenal gland.
 
 
Development Of Adrenal Gland

 

During embryogenesis adrenal gland has two distinctive tissues
  • Adrenal cortex – From mesoderm
    • Fetal cortex (Majority)
    • Adult cortex
  • Adrenal medulla – From neuroectoderm
 
Development Of Adrenal Cortex
   
Urogenital ridge- Mesoderm
          
At 4 weeks, mesothelial cells proliferate and from a cluster of cells known as Adrenal-gonadal primordium
          
At 6 – 7 weeks of gestation, cells migrate into the adrenal primordium
          
Formation of the adrenal cortex
          
Later in after birth, it is replaced completely by adult adrenal cortex
 
 
Development Of Adrenal Medulla 
      
Neural crest cells – Neuroectoderm
          
Migration towards the coelomic cavity wall 
          
Formation of the adrenal medulla (Uncapsulated)
          
Later become engulfed by the adrenal cortex to become encapsulated 



Adrenal Cortex In Fetal Life
     
Two types of cortices are seen in fetal life.
Soon after development of the fetal cortex (At around 7 months), they start to secrete steroids.
At 4 months of gestation – Adrenal gland is 4x larger than the kidney
At birth – Adrenal gland is 1/3rd of the size of the kidney, because of the rapid regression of the  fetal adrenal cortex 
At 4 years – Fully developed cortex
  • Fetal adrenal cortex
    • Major proportion of the adrenal cortex is composed of the fetal cortex
  • Adult adrenal cortex
    • Very small proportion of the total cortex
    • Adult type zona glomerulosa and fasciculata is seen in fetal life
    • Zona reticularis is not seen during fetal life
    • Zona reticularis begins to appear at 3 years of age
    • At 4 years – Fully developed cortex
 
Adrenal Medulla In Fetal Life
  • Composed of two types of cells that secrete adrenaline and noradrenaline 
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