Pituitary stalk and the hypophyseal portal veins

Pituitary · detail · Portal veins Watershed supply Sheehan

Releasing hormones reach the anterior lobe only through the long portal veins running down the stalk from the median eminence. The anterior lobe has no direct arterial supply; the posterior lobe is fed directly by the inferior hypophyseal artery.

Traced from the start

Detail

Route: Superior hypophyseal artery to the primary plexus in the median eminence, then long portal veins, then the secondary sinusoidal plexus of the pars distalis
Consequence: The adenohypophysis is watershed tissue vulnerable to hypotension; the neurohypophysis, on a direct arterial supply, is not

When it goes wrong

Severe postpartum haemorrhage with hypotension (Sheehan syndrome)

Infarction of the hyperplastic anterior pituitary: failure to lactate first, then failure to resume menses, loss of axillary and pubic hair, and later hypothyroidism and adrenal insufficiency; the posterior lobe is usually spared

Haemorrhage into a pituitary adenoma (apoplexy)

Sudden severe headache, vomiting, ophthalmoplegia from cavernous sinus nerve compression and visual loss; give parenteral hydrocortisone immediately

Stalk compression by a suprasellar mass

Loss of dopamine delivery raises prolactin modestly while every other anterior axis fails

Practise this structure

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