Education Resource from the Society for Endocrinology
P Statham
Western General Hospital, Edinburgh
Endocrine Nurses Training Course 10-12
September 2003
St Aidan's College, University of Durham, Windmill Hill, Durham DH1 3LJ
Pituitary surgery has evolved since the 1930s with improvements in technology. As technology has improved, the indications for surgery have increased. However medical advances, particularly with dopamine agonists, and improved delivery of radiotherapy have limited the present role of surgery.
The decision as to whether a patient should have operative treatment of their pituitary disease is dependent on the patient, the disease, the availability of other treatments, and of a suitable surgical team, who produce reliable results.
Pituitary disease suitable for surgery can be categorised as:
Hypersecretion syndromes, particularly acromegaly, Cushings disease and occasional patients with hyperprolactinaemia.
Mass effect from macroadenomas(tumours over 1cm in diameter), with suprasellar extension, from craniopharyngiomas, and from other cysts. Occasionally other conditions occur mimicking these, including abscess, hypophysitis (an inflammation of the pituitary gland, often of autoimmune origin) and rarer tumours such as germinoma or metastasies.
Enlargement of pituitary tumours causes headache, particularly if sudden, visual field defects, because of the proximity of the optic chiasm, hypopituitarism, because of squashing of the adjacent pituitary gland and occasionally, with very big tumours, epilepsy or hydrocephalus. Enlargement superiorly may block the foramen of Munro, causing hydrocephalus,and superolaterally may compress the medial temporal lobe, a very epileptogenic area of the brain.
Pituitary apoplexy is a clinical condition, fortunately rare, characterised by headache, drowsiness, hypotension and opthalmoplegia. It occurs as a consequence of sudden enlargement of an already large pituitary macroadenoma, with venous infarction and swelling of the tumour. This compresses the cavernous sinus, causes haemorrhage into the subarachnoid space, and acute hypopituitarism, leading to hypotension.
This must include a full endocrinological assessment of anterior and posterior pituitary function. The most important immediate result is the Prolactin level, as this determines whether treatment with a dopamine agonist such as bromocyptine or cabergoline would be better. A high prolactin does not necessarily mean that a tumour will shrink with a dopamine agonist, as a moderate rise to about 10 times normal can occur as a result of lack of inhibition of dopamine release, when the pituitary stalk is compressed. A clinical judgement has to be made about this.
The patient’s visual fields should also be assessed, together with colour vision, visual acuity and the fundoscopy. If pallor of the optic disc is present the prospects for improvement in the visual field, as a result of decompression, are less likely. Coexistence of cataracts, or macular degeneration, can sometimes cause diagnostic confusion, and influence the benefit from surgery.
The general medical condition, and occasionally psychiatric condition, needs to be assessed. Macroadenomas are found in the elderly who may have other medical conditions which pose a significant anesthetic risk.
Magnetic Resonance (MR) scanning has become the most useful imaging in the management of patients with pituitary tumours. Particular attention must be drawn to the possibility of a tuberculum sellae meningioma, an uncommon site of tumour , but which cannot easily be removed through the transphenoidal approach. Excluding a Carotid aneurysm is vital, as a mistaken transphenoidal approach would be likely to be fatal. The small adenomas of Cushing’s disease and acromegaly, are increasingly being identified with modern MR.
For patients with hypersecretion syndromes surgical treatment often has the likelihood of cure, so most patients want to get on with it as soon as possible. In the elderly with a macroadenoma if the field defect is modest, or the tumour picked up incidentally when they were having a scan for another condition, it may be appropriate to wait and see the speed of tumour growth, by arranging serial MR scans 6-12 months apart.
Transphenoidal operation is the preferred approach for most pituitary rumours. This is because it is least invasive, leading to faster recovery. With modern microscopes and endoscopes a good view of the pituitary fossa is available. CSF leaks, which occur in up to 10% of operations are treated with a spinal drain for 48 hours after the operation.
Transcranial operation is necessary for a few very large pituitary macroadenomas, and and for pituitary cysts, particularly craniopharyngioma, and for meningiomas. These tumours are either too hard and vascular, or too stuck to adjacent structures (anterior cerebral arteries, optic nerves, frontal lobes of the brain) to be able to use the transphenoidal route.
3 day cortisol level, one month anterior and posterior pituitary function assessment, and a 3 month check MR scan are normally performed on all patients. After this a decision is made about whether radiotherapy should also be given, to reduce the risk of recurrence of tumour.
Yearly endocrinological follow up, with imaging if required then follows.
The opinions expressed in this paper are those of the speaker and do not necessarily reflect the views of the Society