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, it regulates the functioning of almost all the systems of our body.
The pituitary gland may be affected by small benign tumors, defined as pituitary adenomas . Adenoma is a benign tumor that develops slowly from epithelial glandular cells .
Considering that the pituitary gland is a gland dedicated to the secretion of hormones that regulate numerous functions of the organism, all the tumors that strike 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 adenohypophysis adenomas .
Classification
Pituitary adenomas have been classified according to various parameters, but mainly they differ according to their size and their functional characteristics .
- Based on size . Pituitary adenomas are classified anatomically as a function of the size of the tumor mass, established on the basis of radiological findings: tumors less than 1 cm in diameter are called microadenomas, while those with a diameter greater than 1 cm are called macroadenomas .
- Based on the degree of infiltration .
- Benign adenoma : almost all pituitary adenomas are benign (non-cancerous), grow very slowly and do not spread from the pituitary gland 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, capable of spreading to other areas of the central nervous system (brain and spinal cord) or to other parts of the body.
- Based on the extension . The pituitary gland in the adult is housed in the turgical saddle, a small bone cavity at the base of the skull. If the tumor is confined within the turgical saddle the adenoma is defined as intramural, while if it is extended outside this cavity it is extrasellar .
- From the clinical / functional point of view . Pituitary adenomas can be classified according to the clinical picture, characterized by the excessive secretion of one of the pituitary hormones.
- Secreting . Pituitary adenomas that cause an increased secretion of a specific active hormone are called functioning adenomas
- Not secreting . The non-functioning adenomas are instead 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 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 gland.
Functional pituitary adenomas
The pituitary gland consists 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). Tumor pituitary cells, which define a functioning adenoma, produce an excess of one or more hormones and the consequent alteration of the target organs (thyroid, adrenal glands and sexual glands). The hyperactivity or hypo-activity affecting the pituitary thus affects the entire system.
Hormones produced by the pituitary gland | |
Adenopofisi | 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 (respectively, triiodothyronine and thyroxine). |
Prolactin | It acts on the development of the mammary gland and, after giving birth, induces the secretion of milk. |
Follicle-stimulating hormone (FSH) | In females: stimulates the growth and development of ovarian follicles and estrogen secretion; in males: stimulates sperm production 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 from the kidneys; promotes vasoconstriction (arterioles). |
Oxytocin | In females: it stimulates uterine contractions and, during lactation, the expulsion of milk from the mammary glands. |
Functioning pituitary adenomas are subdivided, therefore, according to the hypersecret hormone:
- Prolactin-secreting adenomas ( prolactinoma ): in about 50% of functioning pituitary adenomas, the affected cells are those that secrete prolactin, with a symptomatology that includes secretory anomalies of the mammary glands (galactorrhea), irregularity of the menstrual cycle (amenorrhea) and sometimes even sexual dysfunction. See: hyperprolactinemia
- GH-secreting adenomas : cells that secrete growth hormone are affected in approximately 30% of functioning pituitary adenomas. If it occurs in children, it manifests with gigantism (excessive statural growth) or with acromegaly in adults (excessive thickening of the bones and excessive growth of the soft tissues).
- ACTH-secreting adenomas : cells that secrete ACTH are affected in about 20% of functioning pituitary adenomas; the symptomatology, called Cushing's syndrome, includes hyperglycemia due to excessive secretion of cortisol (which can lead to diabetes mellitus), obesity of the trunk but not in the limbs, purple streaks in the abdomen (signs of stretch) due to collagen deficiency in the rounded skin and face due to fluid accumulation.
- Other pituitary secretory cells can also be affected, but this occurs less frequently.
Functional pituitary adenomas are generally diagnosed early on the basis of symptoms arising from hormonal imbalances. As a result, most of the detected functional adenomas are microadenomas.
Incidence
Pituitary adenomas are relatively common: they represent 10% of all intracranial neoplasms and the estimated prevalence rate in the general population is about 17%. Most of these tumor masses do not grow or cause obvious disorders. Pituitary adenomas may present in patients of any age, including pediatric patients. The peak incidence is between 30 and 60 years (20-45 years in women; 35-60 years in men). In many cases, the mode of presentation is accidental: often the doctor finds a pituitary adenoma while the patient is undergoing an MRI scan of the brain (10% of cases) or a CT (computed tomography) for another reason.
