Content Reviewers:Rishi Desai, MD, MPH
The pituitary gland, is a small gland with a diameter of approximately 1 cm.
It sits within a saddle-shaped bony cavity called the sella turcica, at the base of the brain.
The gland is divided into two main parts, the anterior pituitary or adenohypophysis; and the posterior pituitary or neurohypophysis.
Each part originates from different embryological sources, which is reflected in their different structure and function.
“Adeno” means “related to glands” and the adenohypophysis consists primarily of glandular epithelial tissue.
In comparison, the neurohypophysis consists mainly of neural secretory tissue, since the neurohypophysis arises from a bud of nervous tissue that grows down from the hypothalamus.
In this low power, para-sagittal section of the pituitary gland, the anterior and posterior parts of the pituitary can be identified pretty easily when stained with Masson’s trichrome.
Generally, this stain will stain nuclei and basophilic structures blue, collagen will be blue or green, and non-basophilic cytoplasm and red blood cells will be red.
The posterior pituitary is composed of mostly unmyelinated axons, which don’t have nuclei or a large amount of collagen.
So as a result, the posterior pituitary doesn’t stain well and will look significantly lighter when compared to the anterior pituitary.
Whether it’s stained with Masson’s trichrome or Hematoxylin and eosin.
In between the anterior pituitary and posterior pituitary, is a thin strip of cystic tissue, called the pars intermedia, which is part of the anterior pituitary because the cysts are actually remnants of Rathke’s pouch, which is the embryological structure that eventually develops into the anterior pituitary.
Zooming in closer to the pars intermedia, the colloid-filled cysts can be seen more clearly, along with irregular clusters of basophilic cells, that often invade the neighboring neurohypophysis as well.
Looking even closer, we can see a portion of the pars intermedia that has an area of lymphocyte infiltration.
It’s also easier to see that the adenohypophysis has a much richer blood supply compared to the neurohypophysis, with many small blood vessels present throughout the adenohypophysis, including the pars intermedia.
Alright, let’s move anteriorly and take a closer look at the adenohypophysis.
Besides the bright red erythrocytes, there are two main groups of cells that are named based on how well they stain.