The pituitary gland has a dual blood supply. The superior hypophyseal arteries arise from the internal carotid artery and supply the pituitary stalk and the anterior pituitary via a hypophyseal portal system, carrying hypothalamic releasing hormones from the median eminence to the anterior pituitary cells. The inferior hypophyseal arteries arise from the meningohypophyseal trunk of the cavernous ICA and supply the posterior pituitary (neurohypophysis) directly.
The pituitary portal system is the functional mechanism by which hypothalamic hormones (GnRH, TRH, CRH, GHRH, somatostatin, dopamine) regulate anterior pituitary function. Disruption of the pituitary stalk by trauma, surgery, or tumour interrupts the portal system and causes pan-hypopituitarism from loss of hypothalamic stimulation, along with paradoxical hyperprolactinaemia from loss of dopamine inhibition. In transsphenoidal pituitary surgery, preservation of the superior hypophyseal arteries and the stalk is essential to prevent post-operative anterior pituitary insufficiency.
Trauma, surgery, or compression of the pituitary stalk disrupts superior hypophyseal portal flow, producing central diabetes insipidus from posterior pituitary disconnection, pan-hypopituitarism from loss of hypothalamic stimulation, and paradoxical hyperprolactinaemia, requiring lifelong hormone replacement therapy.
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