A macroadenoma that secretes prolactin is usually associated with a serum prolactin level of more than 200ng/ml (4,000mu/l). The macroadenoma is visualised with CT or MRI. If the patient has a macroadenoma and a serum prolactin level of less than 200ng/ml (4,000mu/l), consideration should be given to the possibility that a non functioning pituitary adenoma is present; here, the hyperprolactinaemia results from deprivation of some lactotrophs of dopaminergic inhibition. Enlargement of the pituitary fossa on a skull X-ray may represent the expansion of the fossa by the macroadenoma, but care should be exercised to exclude the possibility of cisternal herniation (a partially empty fossa) as a cause for the enlargement. CT and MRI scans are proving useful here.
