Prolactinoma

• prolactinoma is the most common form of pituitary tumour accounting for approximately 50% of pituitary adenomas
• commonly diagnosed when raised prolactin levels are found during investigation of secondary amenorrhoea or galactorrhoea
• alternative causes of raised prolactin levels includes pregnancy, hypothyroidism and drugs e.g. antipsychotics, anti-emetics
• prolactinomas may occur as part of the MEN-1 syndrome
• pituitary tumours are classified according to size - microadenomas (<1cm) and macroadenomas - prolactinomas are considered in terms of microprolactinomas and macroprolactinomas

Note that non-secretory pituitary adenomas may also cause hyperprolactinaemia - this may occur if a non-secretory adenoma disrupts the flow of hypothalmic dopamine (the physiological prolactin inhibitory factor) to the lactotrophs (the pituitary cells which produce prolactin).

• giant prolactinomas, a rare subtype of macroadenomas, are characterized by large size (over 4 cm), very high prolactin levels (more than 1000 ng/ml) and invasive growth and are thus the most difficult to treat

Reference:

• Melmed S, Casanueva FF, Hoffman AR, et al.Diagnosis and treatment of hyperprolactinemia: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2011;96: 273-288.