Pituitary incidentaloma.

All patients with pituitary incidentaloma should be investigated for pituitary hyperfunction. The single most important test is measurement of serum prolactin (PRL). Elevated PRL can indicate either direct tumour secretion (levels are typically 800–2,000 mU/l for microprolactinoma, >2,000 mU/l for macroprolactinoma and <600 normally) or ‘disconnection’ of the hypothalamus and normal pituitary gland by a large nonfunctioning pituitary mass (PRL usually <2,000 mU/l). In patients with raised PRL, it is important to consider PRL-elevating drugs (eg domperidone), hypothyroidism and ‘macroprolactin’ (an assay artefact caused by PRL-binding immunoglobulin G, which is present in approximately 1% of normal individuals). Hypogonadism (with implications for bone thinning as well as sexual dysfunction) can occur with any degree of hyperprolactinaemia. Although acromegaly is a rare cause of pituitary incidentaloma, it is an important diagnosis to make as early as possible; insidious symptoms of acromegaly might have been overlooked until the time of incidentaloma discovery. The best single test for acromegaly is measurement of serum Epidemiology, aetiology and natural history