= hypophysis cerebri within hypophyseal fossa of sphenoid, covered superiorly by sellar diaphragm (= dura mater) which has an aperture for the infundibulum centrally
Size: (adult size is achieved at puberty)
Height in adult females: 7 (range 4–10) mm
Height in adult males: 5 (range 3–7) mm
(normal height in men aged 40–49 = 4.89 ± 0.87 mm)
Shape:
- flat / downwardly convex superior border
- upwardly convex during puberty, pregnancy, in hypothyroidism (due to hyperplasia)
Anterior Lobe of Pituitary Gland
= larger anterior portion of adenohypophysis comprising 80% of pituitary gland volume
Origin: ectodermal derivative of stomadeum
Function:
- chromophil cells
- acidophil cells = α cells
- growth hormone = somatotropin (STH)
- prolactin = lactogenic hormone (LTH)
- basophil cells = β cells
- adrenocorticotropic hormone (ACTH)
- thyrotropin = thyroid-stimulating hormone (TSH)
- follicle-stimulating hormone (FSH)
- interstitial-cell-stimulating hormone (ICSH)
- luteinizing hormone (LH)
- melanocyte-stimulating hormone (MSH)
- acidophil cells = α cells
- chromophobe cells
50% of epithelial cell population, of unknown significance
MR:
- larger homogeneous component isointense to white matter on T1WI + T2WI
- prominent contrast enhancement (during first 3 minutes) ← lack of blood-brain barrier
- hyperintense in newborn fading to normal adult signal by 2nd month of life
Pars Intermedia of Pituitary Gland
= posterior portion of adenohypophysis, separated from anterior lobe by hypophyseal cleft in fetal life
Origin: Rathke cleft / Rathke pouch within intermediate lobe of pituitary gland
Function: termination point of short hypothalamic axons elaborating tropic hormones (= releasing factors + prolactin inhibiting factor), which are carried to anterior lobe via the portal system
- not visible with imaging techniques
Posterior Lobe of Pituitary Gland
= major portion of neurohypophysis
= termination point of neurosecretory axons from supraoptic and paraventricular nuclei of hypothalamus (= hypothalamohypophyseal tract)
Origin: diencephalic outgrowth
Function: storage site for transported
- vasopressin (= antidiuretic hormone [ADH])
- oxytocin
MR:
- crescent of T1-hyperintensity + T2-isointensity compared with anterior pituitary lobe ← lipid in glial cell pituicytes + phospholipids of vasopressin
- isointense in 10% of normal individuals
Pituitary Stalk / Infundibulum
Origin: arises from anterior aspect of floor of 3rd ventricle (infundibular recess)
Histo: formed from axons of cells lying in supraoptic + paraventricular nuclei of hypothalamus
- joins posterior lobe at junction of anterior + posterior lobes
- up to 3 mm thick superiorly, up to 2 mm thick inferiorly
- usually in midline, may be slightly tilted to one side
MR:
- prominent contrast enhancement