Pituitary tumours

Introduction

Pituitary tumours account for 8 per cent of all intracranial tumours. Historically they were classified according to their staining characteristics seen on light microscopy. However, the three types (chromophobe, acidophilic and basophilic) did not correspond closely with the clinical syndromes of pituitary hypersecretion. The subsequent development of immunological staining techniques and electron microscopy provided a more refined classification of pituitary tumours. It is now correct to classify pituitary tumours according to their size (microadenomas, mesoadenomas and macroadenomas) and whether they are endocrine active or inactive (Table 35.5). These features will also determine their presentation.

Clinical features

Pituitary tumours arise in the sella tercica and can expand up into the suprasellar cisterns, compressing the optic chiasm above and resulting in visual failure — classically a bitemporal hemianopia. Careful assessment of the visual fields, visual acuity and optic fundi is therefore essential. They may also invade laterally into the cavernous sinuses on each side, compressing the third to fourth cranial nerves.

Endocrine disturbance is due to either hypopituitarisrn or excess secretion of a particular pituitary hormone. Prolactin secreting tumours are usually found in younger women and cause loss of libido, infertility, amenorrhoea and galactorrhoea. Corticotrophin-producing tumours cause Cushing’s disease due to cortisol excess. The principal features are moon face, abdominal striae, buffalo hump, hypertension and diabetes mellitus.

Acromegaly is due to an overproduction of growth hormone. The disease is disfiguring, causing prognathism and overgrowth of joints, especially in the hands and feet. Systemic side effects include hypertension, cardiomyopathy, diabetes mellitus, excessive sweating, arthralgias and lassitude. Haemorrhage into a macroadenoma, known as pituitary apoplexy, can precipitate an acute presentation with headache, hypopituitarism and visual failure. Diabetes insipidus, a product of direct hypothalamic involvement, is usually indicative of a craniopharyngioma and rarely caused by pituitary tumours.

Investigation

Diagnosis is confirmed by laboratory assessment of pituitary endocrine function, neuroradiological imaging (Fig. 35.33) and formal visual assessment.

Radioimmunoassay will identify the hormone being secret­ed. It is important, particularly with acute presentations, to exclude a prolactinoma as the majority of these will respond rapidly to treatment with the dopamine antagonist bromocriptine. Prolactin levels above 200 ng/ml ate usually diagnostic. Nonfunctioning macroadenornas may cause hyperprolactinaemia due to distortion of the pituitary stalk or impingement on the hypothalamus. This is because the latter produces prolactin-inhibiting factor, which under nor­mal circumstances suppresses prolactin levels to below 15 ng/ml. Diagnosis of Cushing’s disease is made by radioimmunoassay of adrenocorticotrophic hormone (ACTH) in the peripheral blood and petrosal venous sinus sampling.

With the exception of some patients with Cushing’s disease, MRI of the sella will confirm diagnosis of an intrasellar mass. The resolution of MRI will also detect all but the smallest (<2 mm) tumours and any extrasellar extension.

Treatment

Treatment depends on the endocrine disturbance present and the effect of compression of adjacent neural structures. For prolactinomas, bromocriptine (a dopamine agonist) is commenced. Surgical excision is reserved for macroadenomas compressing the optic chiasm, growth hormone secreting tumours causing acromegaly and ACTH secreting tumours causing Cushing’s disease. Occasionally surgery is under­taken in patients with prolactinomas not responding to medical treatment or when unwanted side effects occur. This is usually performed via a transphenoidal route although the transcranial route can be employed. The aim is to preserve normal pituitary function if possible. Surgery should be covered with parenteral hydrocortisone and frequently vasopressin is requited.

Radiotherapy is used for subtotal resections and for persistent hypersecretion of pituitary hormones. The long-term follow-up of nonfunctioning pituitary adenomas has shown a recurrence rate approaching 40 per cent at 10 years indicating that there is perhaps a more extensive role for this modality and that postoperative patients should be more closely followed up.