Pituitary Gland, Hypothalamus, and Pineal Gland - Pathology

PITUITARY GLAND, HYPOTHALAMUS, AND PINEAL GLAND

Pituitary adenomas are categorized as follows:

•         Microadenoma if <1 cm

•         Macroadenoma if >1 cm

Macroadenomas cause visual field defects.

GNAS1 mutations are common. Pathologically, adenomas are monomorphic com-pared with normal pituitary.

•         Prolactinoma is the most common type of pituitary adenoma. Lactotroph cells secrete prolactin, which results in hyperprolactinemia. Clinical features include galactorrhea, amenorrhea, and infertility, or decreased libido and impotence.

•         Nonfunctional adenoma may produce hypopituitarism.

•         Growth-hormone–producing adenoma is characterized by elevated growth hormone (GH) and elevated somatomedin C (insulin-like growth factor 1 [IGF-1]). It causes gigantism in children and acromegaly in adults.

Sheehan syndrome is ischemic necrosis of the pituitary secondary to hypotension from postpartum hemorrhage resulting in panhypopituitarism.

Posterior pituitary syndromes include the following:

•         Diabetes insipidus

°°    Central diabetes insipidus is caused by ADH deficiency, which results in hypotonic polyuria, polydipsia, hypernatremia, and dehydration. Causes include head trauma and tumors.

°°    Nephrogenic diabetes insipidus is caused by a lack of renal response to ADH.

•         Syndrome of inappropriate ADH secretion (SIADH) is caused by excessive pro-duction of antidiuretic hormone (ADH), resulting in oliguria, water retention, hyponatremia, and cerebral edema. Causes include paraneoplastic syndrome and head trauma.

Craniopharyngioma is a benign pituitary tumor derived from Rathke pouch rem-nants that is usually located above the sella turcica, but can extend downward to destroy the pituitary. It is the most common cause of hypopituitarism in children.

Hypothalamic disorders can cause a variety of problems:

•         Hypopituitarism (including dwarfism) can be due to a lack of releasing hor-mones from the hypothalamus.

•         Central diabetes insipidus is due to lack of ADH synthesis.

•         Precocious puberty is usually due to a midline hamartoma in boys.

•         The hypothalamus can also be affected in hydrocephalus.

•         Visual field changes can complicate hypothalmic disorders.

•         Masses can affect the hypothalamus, i.e., pituitary adenoma, craniopharyn-gioma, midline hamartoma, and Langerhans histiocytosis.

•         Inflammatory processes can affect the hypothalamus, i.e., sarcoidosis and meningitis.

Pineal diseases include dystrophic calcification (a useful landmark for radiologists) and rarely tumors, with most being germ cell tumors.