PITUITARY AND PITUITARY ADENOMAS - DEFINITION, CLASSIFICATION, INCIDENCE - NERVOUS-SYSTEM-HEALTH

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Pituitary adenoma

Pituitary gland

The pituitary gland (or pituitary gland) is a primary endocrine gland, whose main function is the secretion of hormones with which, together with the hypothalamus that controls it, regulates the functioning of almost all the systems of our body.

The pituitary gland is located at the base of the brain, just behind the eyes, and has a pea-sized oval structure connected to the hypothalamus by a thin tissue stalk. The pituitary is divided anatomically and functionally into two distinct lobes: adenohypophysis (or anterior pituitary) and neurohypophysis (or posterior pituitary).

The pituitary gland may be affected by small benign tumors, referred to as pituitary adenomas. Adenoma is a benign tumor that slowly develops from epithelial glandular cells.

Considering that the pituitary is a gland responsible for the secretion of hormones that regulate numerous functions of the organism, all the tumors that affect it are potentially dangerous, even if of a benign nature. Pituitary tumors represent about 10% of all intracranial tumors and in 90% of cases are adenomas of the adenohypophysis.

Classification

Pituitary adenomas have been classified according to various parameters, but they are mainly distinguished according to their size and functional characteristics.

According to the size. Pituitary adenomas are classified anatomically according to the size of the tumor mass, established on the basis of radiological tests: tumors with a diameter of less than 1 cm are defined as microadenomas, while those with a diameter greater than 1 cm are defined as macroadenomas.
According to the degree of infiltration.
- Benign adenoma: Almost all pituitary adenomas are benign (non-cancerous), grow very slowly and do not spread from the pituitary to other parts of the body.
- Invasive adenoma: some tumors can grow quickly, infiltrating or compressing the structures adjacent to the pituitary gland (optic chiasm, cavernous sinus, hypothalamic nucleus, etc.).
- Carcinoma (metastasizing): These are extremely rare malignant tumors that can spread to other areas of the central nervous system (brain and spinal cord) or to other parts of the body.
Based on its extension. The pituitary gland in the adult is housed in the turgic sella, a small bony cavity at the base of the skull. outside this cavity is extrasellar.
From a clinical / functional point of view. Pituitary adenomas can be classified according to the clinical picture, whether or not it is characterized by excessive secretion of one of the pituitary hormones.
- Secretaries. Pituitary adenomas that cause increased secretion of a certain active hormone are called functioning adenomas
- Non-secreting.Non-functioning adenomas, on the other hand, are made up of inactive tumor cells, which tend to depress the secretion of other hormones by compressing non-tumor endocrine cells, or they can cause neurological disorders by compressing neurons that are located in the vicinity of the tumor. A common neurological symptom is, in fact, blurred vision, since the optic nerves are located very close to the pituitary.

Functioning pituitary adenomas

The pituitary gland is made up of different types of pituitary cells and each of these participates in the production of particular hormones released into the bloodstream. The pituitary adenoma originates from one of these specialized cells (tumor = monoclonal expansion). The tumor pituitary cells, which define a functioning adenoma, produce an excess of one or more hormones and the consequent altered stimulation of the target organs (thyroid, adrenal and sex glands). The hyperactivity or hypoactivity affecting the pituitary thus affects the entire system.

Hormones produced by the pituitary gland

Adenopophysis

Normal physiological function

Growth hormone (GH)

Essential for growth; stimulates bone and soft tissue growth; regulates the metabolism of proteins, lipids and carbohydrates.

Adrenocorticotropic hormone (ACTH)

It stimulates the adrenal cortex to secrete glucocorticoids.

Thyroid-stimulating hormone (TSH)

It stimulates the thyroid to secrete T3 and T4 (triiodothyronine and thyroxine respectively).

Prolactin

It acts on the development of the mammary gland and, after childbirth, induces the secretion of milk.

Follicle-stimulating hormone (FSH)

In females: it stimulates the growth and development of ovarian follicles and the secretion of estrogen; in males: stimulates the production of spermatozoa in the testicles.

Luteinizing hormone (LH)

In females: it stimulates ovulation, the transformation of the ovarian follicle into the corpus luteum and the secretion of estrogen and progesterone; in males: it stimulates the testicles to produce testosterone.

Neurohypophysis

Antidiuretic hormone (ADH) or vasopressin

Reduces urinary excretion by the kidneys; promotes vasoconstriction (arterioles).

Oxytocin

In females: it stimulates uterine contractions and, during breastfeeding, the expulsion of milk from the mammary glands.

Functioning pituitary adenomas are therefore subdivided according to the hypersecreted hormone:

Prolactin-secreting adenomas (prolactinoma): in about 50% of functioning pituitary adenomas, the affected cells are those that secrete prolactin, with symptoms that include secretory abnormalities of the mammary glands (galactorrhea), irregular menstruation (amenorrhea) and sometimes even sexual dysfunctions. See: hyperprolactinemia
GH-secreting adenomas: cells that secrete growth hormone are affected in about 30% of functioning pituitary adenomas. If it occurs in children it manifests itself with gigantism (excessive statural growth) or with acromegaly in adults (excessive thickening of the bones and soft tissue overgrowth).
ACTH-secreting adenomas: ACTH-secreting cells are affected in about 20% of functioning pituitary adenomas; the symptoms, called Cushing's syndrome, include hyperglycemia due to excessive secretion of cortisol (which can lead to diabetes mellitus), trunk obesity but not in the limbs, purple streaks in the abdomen (stretch marks) due to collagen deficiency in the rounded skin and face due to the accumulation of fluids.
Other secretory cells of the pituitary may also be affected, but this occurs less frequently.

Functioning pituitary adenomas are usually diagnosed early based on symptoms resulting from hormonal imbalances. Consequently, most of the detected functioning adenomas are microadenomas.

Incidence

Pituitary adenomas are relatively common: they account for 10% of all intracranial neoplasms and the estimated prevalence rate in the general population is about 17%. Most of these tumors do not grow or cause noticeable disturbances. Pituitary adenomas can present in patients of any age, including pediatric age. The peak incidence is between 30 and 60 years (20-45 years in women; 35-60 years in men). In many cases, the presentation is accidental: often, the doctor finds a pituitary adenoma while the patient is undergoing an MRI of the brain (10% of cases) or CT (computed tomography) for another reason.