PITUITARY TUMORS

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Pathology assignment 
Thota Vaishnavi 
Roll no. 133

PITUITARY GLAND

Introduction
The Pituitary gland is a small bean, bean shaped structure that lies at the base of the brain within the sella turcica. It is composed of two morphologically and functionally distinct components: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).
The anterior Pituitary which constitutes about 80% of the gpand, produces trophic hormones that stimulate the production of hormones from thyroid, adrenal and other glands.
The posterior Pituitary consists of modified glial cells (termed pituicytes) and axonal processes extending from the hypothalamus through the Pituitary stalk to the posterior lobe (axon terminals).

Pituitary Adenomas and Hyperpituitarism

The most common cause of hyperpituitarism is an adenoma arising in the anterior lobe.

Classification

Pituitary adenomas are classified on the basis of the hormones and cell type specific transcription factors that are expressed by the tumor cells.

Some Pituitary adenomas secrete two hormones ( GH and prolactin being the most common combination ), and rarely, pituitary adenomas are plurihormonal. Less common causes of hyperpituitarism include pituitary carcinomas and some hypothalamic disorders. 
Pituitary adenomas may be functional or non-functional.
1. Functional tumors: They are classified depending on the hormones produced by the tumor cells ( detected by immunohistochemical stains on tissue sections). These hormones lead to endocrine abnormalities. They predominantly produce a single hormone. Some may secrete two different hormones ( e.g., growth hormone and prolactin) and rarely they may produce many hormones.
▪︎ Lacatotroph adenomas: Prolactin-secreting lactotroph adenomas are the most common type ( about 30% ). Hyperlactinemina clinically causes amenorrhea, galactorrhea, loss of libido, and infertility.
▪︎ Somatotroph adenomas: Growth hormone secreting somatotroph adenomas are the second most common type of functioning pituitary adenoma. They produce gigantism in children or acromegaly in adults.
▪︎ Corticotroph adenomas: Excess production of ACTH leads to adrenal hypersecretion of cortisol and the development of hypercorticosolism ( Cushing syndrome ). 
2. Non-functional tumors:
▪︎ Mass effetcs: They do not produce any hormone but produce mass effects.
▪︎ Silent tumors: The hormone production can be demonstrated at the tissue level only and are without clinical manifestations of hormone excess.

Pathogenesis 

Many genetic abnormalities have been indentifies. These include: 
▪︎ G- protein mutations: G- proteins play a major role in signal transduction, transmitting signals from cell surface receptors to intracellular effectors, which in turn generate second messengers.
▪︎ Genetic predisposition: About 5% of pituitary adenomas have genetic predisposition and 4 genes have been identified as a cause of familial pituitary adenomas. These include MEN1, CDKN1B, PRKAR1A, and AIP. These genes regulate transcription and the cell cycle.
▪︎ Molecular abnormalities: The aggressive tumors are associated with aberrations in cell cycle checkpoint genes ( e.g., overexpression of cyclin D1 ), mutations of TP53, and epigenetic silencing of the retinoblastoma gene ( RB ).

Morphology 
 
Gross

Usually  these tumors are well circumscribed and soft. Small tumors may be confined to the sella turcica, whereas larger tumors may compress the optic chiasma and adjacent structures. About 30% of tumors are nonencapsulated and infiltrate adjacent bone and dura. There may be foci of hemorrhage and/or necrosis in larger adenomas. Depending on the size they are classified as:
• Microadenomas: Size less than 1cm in diameter.
• Macroadenomas: Size more than 1cm in diameter. They may encroach upon and destroy adjacent anterior pituitary parenchyma and may produce hyperpituitarism.

Microscopy

Both functional and nkn- functioning pituitary adenomas are composed of a single cell type. The tumors consists of relatively uniform, polygonal cells arranged in sheets, cords or papillae. The cytoplasm may be acidophilliv, basophilic or chromophobic depending on the type and amount of secretory product within the cell. Thr nuclei of the tumor cells may be uniform or pleomorphic and mitotic figures are very few. The connective tissue or rericulin between the tumor cells is minimal.



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