Prolactinomas are the commonest hormone-secreting pituitary adenomas and the only ones likely to be encountered in routine obstetric practice. They arise from the monoclonal proliferation of a lactotroph cell in the anterior pituitary gland. These cells synthesise and secrete prolactin (PRL), the hormone that promotes lactation. Of these adenomas, 90% are microadenomas (<10 mm diameter) and 10% are macroadenomas (>10 mm). Microadenomas may regress spontaneously and do not usually grow significantly, with very few enlarging to become macroadenomas. Macroade-nomas are more likely to expand1.
The clinical features are due to hyperprolactinaemia and the space-occupying effects of the tumour. Hyperprolac-tinaemia causes secondary amenorrhoea and infertility; it inhibits pulsatile GnRH (gonadotropin releasing hormone) release which results in anovulation and low oestrogen levels. Raised PRL levels can also cause galactorrhoea.
Serum prolactin is always raised: in general higher levels are seen with macroprolactinomas. It is important to exclude other causes of hyperprolactinaemia (pregnancy, untreated hypothyroidism, antipsychotic and antiemetic drugs) before imaging the pituitary with MRI.
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