Pituitary Masses, Hyperprolactinemia & Apoplexy

Evaluating a sellar mass

Image first. A dedicated pituitary MRI with gadolinium defines size and relations to the chiasm and cavernous sinuses. Adenomas under 1 cm are microadenomas; those 1 cm or larger are macroadenomas. Nonfunctioning adenomas, mostly of gonadotroph lineage, are the most common macroadenomas, while prolactinomas are the most common secreting tumors.

Check the eyes. Any lesion that abuts or elevates the optic chiasm needs formal perimetry. Pressure from below on the crossing nasal-retinal fibers produces bitemporal hemianopia, often beginning in the superior temporal quadrants. Diplopia or ptosis from cranial nerve III, IV, or VI palsy implies cavernous sinus invasion or apoplexy.

Look for hormone excess and deficiency. Every adenoma, including an incidental one, is screened in both directions:

Order of failure and replacement. Compression usually knocks out GH and gonadotropins first, with TSH and ACTH failing last. When cortisol and thyroxine are both deficient, start hydrocortisone before levothyroxine, because thyroid hormone speeds cortisol clearance and raises demand, which can precipitate adrenal crisis. Central hypothyroidism is monitored with free T4, not TSH.

Hyperprolactinemia: causes and pitfalls

Physiology. Lactotrophs are under tonic inhibition by hypothalamic dopamine carried down the stalk. Prolactin, in turn, suppresses GnRH, so excess prolactin causes hypogonadotropic hypogonadism: oligo- or amenorrhea, galactorrhea, and infertility in women; low libido, erectile dysfunction, and infertility in men, who often present late with a macroadenoma and headache or visual loss. Untreated hypogonadism also causes bone loss.

Exclude the mimics first.

• Pregnancy and breastfeeding: always check β-hCG.
• Drugs: risperidone and other antipsychotics, metoclopramide, verapamil, opioids, methyldopa.
• Primary hypothyroidism: high TRH stimulates lactotrophs.
• CKD (reduced clearance) and chest-wall irritation (surgery, herpes zoster, nipple stimulation).

Drug-induced elevations are usually modest. If the drug can be safely changed (for example, risperidone to the prolactin-sparing aripiprazole), switch and recheck; if not, MRI excludes a mass. A prolactin above 250 ng/mL strongly suggests a prolactinoma, and levels roughly track tumor size.

Treating prolactinomas

Dopamine agonists first. Cabergoline, taken once or twice weekly, is first-line for prolactinomas of any size because it is more effective and better tolerated than bromocriptine. It normalizes prolactin, restores gonadal function, and shrinks tumors, often improving visual fields within weeks, so a macroprolactinoma with field loss is still treated medically first. Surgery is reserved for resistance, intolerance, or apoplexy. An asymptomatic microprolactinoma does not require treatment.

Adverse effects. Nausea, orthostatic hypotension, and headache are common. Impulse-control disorders (gambling, hypersexuality) require questioning. Cardiac valvulopathy is associated with the high doses used in Parkinson disease. Shrinkage of an invasive tumor can unmask a CSF leak.

Pregnancy. Stop the agonist once pregnancy is confirmed; for a macroadenoma that is invasive or abuts the chiasm, continuing it through pregnancy is an option. Symptomatic growth occurs in only a few percent of microadenomas but in roughly 1 in 5 untreated macroadenomas. Prolactin rises normally in pregnancy and cannot be used for monitoring, so follow headache and visual fields (regularly for macroadenomas). Obtain a non-contrast MRI and restart the agonist if the tumor grows.

Nonfunctioning adenomas

Surveillance. A hormonally silent microadenoma needs only a repeat MRI in about 1 year, then less often if stable. A macroadenoma without mass effect is reimaged at about 6 months, with visual fields and pituitary function testing.

Surgery. Transsphenoidal resection is indicated for visual field loss, chiasmal compression, or tumor growth. Afterward, watch for new hypopituitarism, disorders of water balance, and CSF leak.

Pituitary apoplexy and Sheehan syndrome

Apoplexy. Sudden hemorrhage or infarction of an adenoma, often previously undiagnosed. Triggers include anticoagulation, major surgery, dopamine agonists, pregnancy, and head trauma. Expect a thunderclap headache, vomiting, visual loss, ophthalmoplegia (CN III most often), meningismus, altered consciousness, and hypotension with hyponatremia from acute ACTH loss. It mimics subarachnoid hemorrhage. MRI best shows the hemorrhagic tumor, and CT can miss it.

Sheehan syndrome. Postpartum hemorrhage with hypotension infarcts the pituitary, which is enlarged in pregnancy. Failure of lactation is the earliest clue, followed by amenorrhea, fatigue, hypothyroidism, and adrenal insufficiency with hyponatremia and hypotension. It can present acutely or years later. Replace hormones, glucocorticoid first.