Pathology

Nearly all tumours are benign pituitary adenomas. The incidence increases with age: 20% of 80-year-olds have small adenomas at postmortem examination. Prolactinomas represent 60–70%, growth hormone-secreting tumours 10%, non-secreting tumours 30% and tumours secreting thyroid-stimulating hormone or adrenocorticotrophic hormone are rare. Less common pituitary lesions are craniopharyngiomas, meningiomas, metastases and granulomatous diseases.

Clinical features

These include endocrine malfunction, visual disturbance and headache.

Endocrine disturbance may be due to abnormal excessive hormone secretion or impaired hormone secretion following damage to hormone-secreting cells. The most common features in adults are infertility, amenorrhoea, loss of libido and hypothyroidism. Acromegaly, gigantism, Cushing’s syndrome, diabetes insipidus and hypoadrenalism occur less commonly.

Visual disturbance occurs because of compression of the optic chiasm and is typically chronic or subacute deterioration of vision in both eyes. The chiasmal lesion leads to a bitemporal hemianopia, especially to red pin, and may lead to reduced acuity. The fundi are usually normal but there may be papilloedema or optic atrophy. Eye movement abnormalities occur if the tumour has expanded into the cavernous sinus and compresses the 3rd, 4th or 6th nerves.

Headache is a late feature and may reflect bony erosion or hydrocephalus.

A rare but important presentation is with pituitary apoplexy, characterized by acute visual disturbance associated with headache, malaise and systemic collapse. This is due to infarction of a pituitary tumour causing swelling and acute adrenal failure. It may occur after postpartum haemorrhage in women with pituitary tumours.

Investigations

A highly elevated serum prolactin level (>4000 mU/l (normal <400)) implies a prolactinoma. More moderate elevations may be seen with other pituitary tumours that block the inhibition of prolactin release by dopamine. The tumours and their relation to other structures, especially the optic chiasm, are best seen on MRI (Fig. 1) but may also be seen on a CT scan with dedicated pituitary views. Endocrine assessment may be required, for example thyroid function, adrenal function, follicle-stimulating hormone and luteinizing hormone.

Fig. 1 MRI scan of a pituitary tumour.

Treatment

Pituitary tumours can be divided into two main categories: prolactin-secreting prolactinomas that can usually be treated with medication alone; and other tumours that require surgery. Prolactinomas respond to dopaminergic agonists such as bromocriptine or cabergoline. These not only prevent secretion of the hormone but also cause tumour shrinkage. Surgery is not usually required unless vision is immediately threatened. Growth hormone-secreting tumours may also respond to dopaminergic agonists or octreotide (an analogue of somatostatin) but other tumour types need surgery if there is any suggestion of neurological compromise. Radiotherapy may be of value in some inoperable cases. Endocrine failure requires appropriate treatment. The prognosis with modern treatment is good.