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An unusual cause of acute bacterial meningitis

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Q1: What is the lesion shown on the magnetic resonance imaging scan (see p 791)?

The scan shows a large pituitary tumour (>10 mm diameter: macroadenoma) extending laterally into the cavernous sinus.

Q2: How does this usually present?

Clinical presentation varies according to the age and sex of the patient and with size of the tumour. In the majority of premenopausal women, the lesion is usually a microadenoma and presents with menstrual abnormalities, infertility, or galactorrhoea. In postmenopausal women and men, pituitary tumours are mostly slow growing lesions that present neurologically with headache or visual field defects; classically bitemporal hemianopia due to compression of the optic chiasm. In men there may be signs of partial or complete hypogonadism. These macroadenomas may enlarge and become locally invasive with extrasellar extension into the cavernous sinus resulting in ophthalmoplegia. A large tumour may compress normal pituitary tissue and cause disturbance in the secretion of other pituitary hormones.1

Giant macroprolactinomas (several cm in diameter) are rare, usually show evidence of extrasellar extension on computed tomography, and are difficult to treat.

Q3: How may this condition present with meningism?

Pituitary tumours may present with meningeal irritation in a number of ways. Pituitary infarction or haemorrhage (apoplexy) is characterised by sudden onset drowsiness, headache, diplopia, and meningism. Rarely, it may be the presenting feature of an underlying asymptomatic tumour, or the complication of a known lesion. These symptoms usually merit lumbar puncture, to exclude the clinical suspicion of infection, and can reveal a sterile and often lymphocytic response.2-4

It is rare that bacterial meningitis is the presenting condition in a patient with an underlying pituitary adenoma. Bacterial infection, however, may rarely complicate and follow pituitary microsurgery.5 For lesions invading or eroding into surrounding areas such as the sphenoid sinus, the resulting skull base defect and CSF leak can act as an entry portal for organisms such asStreptococcus pneumoniae predisposing to meningitis.6-8 Two published reports of fatal bacterial meningitis, one with S pneumoniae, were discovered to have an underlying invading pituitary tumour at postmortem examination.9 ,10

Q4: What is the treatment of the underlying lesion?

Dopamine agonist drugs such as bromocriptine usually lower prolactin concentrations, reduce tumour size, and reduce the degree of complications. Most patients require long term treatment and withdrawal may result in tumour expansion and rising prolactin concentrations. In giant macroadenomas, bromocriptine therapy alone is often inadequate and surgical intervention may be required.6 Treatment with bromocriptine, resulting in tumour regression, can be complicated by the appearance of skull base defects causing CSF rhinorrhoea and even pneumocephalus.6 ,7 ,11 Occasionally, extensive CSF rhinorrhoea has required lumboperitoneal shunting or surgical repair.

Our patient was started on depot testosterone injections and bromocriptine therapy and transsphenoidal resection of the lesion was performed. He remains well with normal biochemistry values.

Q5: What are the causes of hyperprolactinaemia?

The causes of hyperprolactinaemia are:

(1) Hypothalamic diseases

  • Tumour: metastasis, craniopharyngioma, glioma.

  • Infiltration: sarcoidosis, tuberculosis, granuloma.

  • Cranial irradiation.

  • Pseudotumour cerebri.

(2) Pituitary diseases

  • Tumours: prolactinoma, adenoma, meningioma, metastases.

  • Acromegaly.

  • Cushing's disease.

  • Infiltration: sarcoidosis, tuberculosis.

(3) Drugs

  • Dopamine antagonists: chlorpromazine, metoclopramide.

  • Cimetidine.

  • Opiates.

  • Oestrogens.

  • Antihypertensives: verapamil, methyldopa.

(4) Metabolic

  • Hypothyroidism.

  • Chronic renal failure.

  • Liver cirrhosis. (5) Stress

Final diagnosis

Macroprolactinoma with extrasellar extension.