The pituitary stalk effect: is it a passing phenomenon?

Abstract

Most patients with large pituitary tumors do not exhibit hyperprolactinemia as a result of pituitary lactotroph disinhibition (stalk effect). Studies have demonstrated that increased intrasellar pressure is associated with both "stalk effect" hyperprolactinemia and pituitary insufficiency. Our primary hypothesis was that, despite continued disinhibition, lactotroph failure is responsible for normoprolactinemia in patients with large macroadenomas. As a corollary, we proposed that the hyperprolactinemia phase, which presumably would precede the insufficiency/normoprolactinemic state, would more likely be discovered in premenopausal females and go unnoticed in males. Prospective, consecutive surgical series of 98 patients of clinically nonfunctional pituitary adenomas. Lactotroph insufficiency was inferred by the coexistence of insufficiency in another pituitary axis. The existence of pre-operative lactotroph disinhibition was inferred based on comparison of pre- versus post-operative prolactin levels. 87 % of patients with tumor size >20 mm and normoprolactinemia had pituitary insufficiency. Pre-operative prolactin in patients with pituitary insufficiency were lower than those with intact pituitary function. Prolactin levels dropped in nearly all patients, including patients with normoprolactinemia pre-operatively. Premenopausal women had smaller tumors and higher pre-operative prolactin levels compared to males. No premenopausal female exhibited evidence of pituitary insufficiency. Our study provides suggestive evidence that the "stalk effect" pathophysiology is the norm rather than the exception, and that the finding of normoprolactinemia in a patient with a large macroadenoma is likely a consequence of lactotroph insufficiency. In males, the hyperprolactinemia window is more likely to be missed clinically due to an absence of prolactin-related symptoms.

Neuro-Endocrine Recovery After Pituitary Apoplexy: Prolactin as a Predictive Factor

“…This translated in a decreased rate of recovery of pituitary function. Previous studies in patients with pituitary adenomas and stalk syndrome demonstrated an association of normal or elevated serum PRL levels with postoperative recovery from neuro-endocrine deficits [23][24][25][26][27]. With this in mind, we suggest that PRL levels may be helpful for the clinical decision making in patients with pituitary apoplexy, whereas unmeasurable to lower-than-normal values will predict panhypopituitarism and elevated levels may result in neuro-endocrine recovery.…”

Sellar Toxoplasmosis and Nonfunctioning Pituitary Adenoma

“…PRL levels caused by this effect do not seem to correlate with tumor size, stalk deviation, or the degree of stalk compression (6,21). In prolactinoma, there is a correlation between PRL levels and tumor size with macroprolactinoma (>10 mm in diameter) typically being associated with PRL levels >250 mg/L (12,17,22).…”

“…A possible explanation may be the "pituitary stalk effect"-defined by an elevation of PRL caused by the decrease of dopaminergic inhibition of lactotrophs associated with elevated intrasellar pressure by a nonePRL-secreting pituitary tumor (6).…”

Three cases of ectopic sphenoid sinus pituitary adenoma

“…Hyperprolactinaemia is seen in 21% of ESSPA [17] and in 15% of the empty sella syndromes [1]. Some authors suggest it is due to the stalk effect observed in the intrasellar hypertension and consists of impaired dopamine delivery [1,3]. Continuity of the pituitary stalk is essential for adequate development and well-functioning of the pituitary gland [8].…”