Brain tumours and space-occupying lesions

Overview

A space-occupying lesion (SOL) is any mass that takes up room inside the skull: tumour, abscess, tuberculoma, cyst, haematoma or parasitic cyst. Because the skull cannot expand, even a benign mass can kill by raising ICP or compressing the brainstem.

Primary brain tumours are only about 1.5% of all cancers, but they often affect younger people and many gliomas are incurable, so they cause a large share of cancer deaths and disability.

Classification

The WHO classifies tumours by cell of origin and grade (grade 1 = benign, grade 4 = highly malignant).

Risk factors

Most are sporadic. The only proven environmental risk is ionising radiation. Genetic syndromes:

Presentation: the triad

1. Seizures: common with low-grade gliomas in the cortex. Usually focal (twitching with preserved awareness), complex partial with temporal lesions, and may become generalised. A first seizure in an adult needs brain imaging.
2. Raised ICP: headache in only about half; typically at its worst on waking and when straining, with nausea and vomiting, papilloedema. Fast-growing tumours (metastases, glioblastoma) cause marked surrounding vasogenic oedema. Sudden deterioration may mean obstructive hydrocephalus, a neurosurgical emergency.
3. Progressive focal deficit: builds up over days to weeks, unlike the sudden onset of a stroke. Pituitary tumours may also cause endocrine problems.

Localising features

Investigations

• CT with contrast: quick first test; shows mass, oedema, shift, hydrocephalus, calcification and bleeding.
• MRI with and without gadolinium: the best test for tumours. Diffusion-weighted sequences show restricted diffusion in an abscess, which helps rule it out.
• CT chest, abdomen and pelvis: look for a primary, because metastasis is the main differential of a ring-enhancing lesion in an adult.
• Pituitary: hormone profile (prolactin, GH/IGF-1, cortisol, TFTs, LH, FSH, testosterone or oestradiol) and formal visual fields.
• Tissue diagnosis: biopsy (stereotactic) or resection; avoid LP if there is mass effect.

Initial management of any SOL

• ABC and treat seizures.
• Dexamethasone for symptomatic vasogenic oedema, with a proton pump inhibitor (stomach ulcer risk). Give it only once an abscess has been confidently excluded (steroids blunt the response to infection), and avoid it before biopsy if lymphoma is suspected (it can melt the lesion and spoil the histology).
• Antiepileptic (levetiracetam, phenytoin or carbamazepine) if the patient has had a seizure. Patients who have never fitted do not need routine prophylaxis; a brief course around craniotomy is an option. Phenytoin induces liver enzymes and interferes with chemotherapy.
• Hydrocephalus: EVD urgently, then shunt or tumour removal.
• Multidisciplinary team decision on surgery, radiotherapy and chemotherapy.

Common tumours

Cerebral metastases

• Most common intracranial tumour; affect about a quarter of cancer patients.
• Primary sites (approximate): lung about 40%, breast about 15%, then melanoma and kidney/urinary tract (about 10% each), and the remaining quarter from other or unknown sites.
• Usually at the grey-white junction, often multiple, with much oedema.
• Single (up to three) metastasis in a fit patient with controlled systemic disease: surgical resection (or stereotactic radiosurgery), then radiotherapy. Multiple metastases: steroids, radiotherapy, and biopsy only if the primary is unknown.

Gliomas

• Arise from glial cells; diffusely infiltrate surrounding brain, so recurrence after even "complete" resection is the rule (except pilocytic astrocytoma, grade 1, in children).
• Low-grade glioma (grade 2): peak in the fourth decade, often presents with seizures. Awake craniotomy with brain mapping protects speech areas.
• High-grade glioma: anaplastic astrocytoma (grade 3) and glioblastoma (grade 4), the commonest glial tumour, peak in the fifth and sixth decades. Imaging: heterogeneous ring-enhancing mass with central necrosis and oedema; may cross the corpus callosum ("butterfly" glioma).
• Treatment: maximal safe resection, then radiotherapy and temozolomide chemotherapy (carmustine wafers can be placed at surgery). Median survival for glioblastoma is only just over 12 months.

Meningioma

• Arises from the arachnoid cap cells of the meninges; extra-axial; mostly benign, slow growing; commoner in women; about 15–20% of primary tumours.
• Common sites: parasagittal/falx, convexity, sphenoid wing, olfactory groove, CPA.
• Imaging: dural-based, uniformly enhancing mass separate from the brain, often a "dural tail"; may calcify and thicken overlying bone (hyperostosis).
• Small incidental tumours in the elderly: watch and wait. Symptomatic or large: steroids and surgical excision. Recurrence at 10 years is about 10% after complete excision with a dural margin and about 30% after subtotal removal. Difficult sites: radiotherapy or stereotactic radiosurgery.

Pituitary adenoma

• Benign; microadenoma < 10 mm (hormone effects), macroadenoma > 10 mm (pressure effects: bitemporal hemianopia, headache, hypopituitarism).
• Types: prolactinoma about 30%, non-functioning about 20%, GH-secreting (acromegaly) about 15%, ACTH-secreting (Cushing's disease) about 10%.
• Prolactinoma: first-line dopamine agonists (cabergoline, bromocriptine), even for large tumours. GH tumours may respond to somatostatin analogues (octreotide).
• Surgery: trans-sphenoidal (microscope or endoscope) for non-functioning adenomas with chiasm compression (main urgent indication), GH and ACTH tumours, and drug failure. Large tumours may need a craniotomy.
• Complications: CSF leak (about 3%), hypopituitarism, diabetes insipidus (stalk handling; usually transient; monitor urine output and sodium, give desmopressin (DDAVP)). Correct cortisol deficiency around surgery.
• Pituitary apoplexy: bleeding or infarction in an adenoma: sudden headache, visual loss, ophthalmoplegia, drowsiness. IV hydrocortisone first, then surgical decompression if vision is threatened.

Vestibular schwannoma (acoustic neuroma)

• Benign nerve sheath tumour of the vestibular nerve in the cerebellopontine angle; bilateral in NF2.
• Unilateral sensorineural hearing loss, tinnitus, imbalance; later facial numbness (early loss of the corneal reflex), facial weakness, hydrocephalus and brainstem compression.
• Investigation: MRI with gadolinium of the internal auditory meatus; audiometry.
• Small tumours: surveillance; medium: radiosurgery or surgery; large (> 4 cm) or brainstem compression: excision (translabyrinthine, retrosigmoid or middle fossa approaches), with a shunt if needed. Hearing and facial nerve may be lost with big tumours.

Craniopharyngioma and colloid cyst

• Craniopharyngioma: from Rathke's pouch remnants in the sellar/suprasellar area; often in children; cystic and calcified; causes visual loss (bitemporal field defect), growth failure, diabetes insipidus and hydrocephalus. Treated surgically ± radiotherapy.
• Colloid cyst: in the roof of the third ventricle at the foramina of Monro; can block both and cause sudden obstructive hydrocephalus and even sudden death; positional headaches. Treated by endoscopic or open removal, or a shunt.

Brain tumours in children

• In children, no other solid cancer is as common as a brain tumour.
• Older children: mostly infratentorial (posterior fossa):
  • Medulloblastoma: malignant, cerebellar vermis, near the fourth ventricle; can seed down the spine ("drop metastases"); ataxia and hydrocephalus.
  • Ependymoma: floor of the fourth ventricle; hydrocephalus.
  • Pilocytic astrocytoma: cerebellar hemisphere, cyst with an enhancing mural nodule, grade 1, often cured by excision.
• Neonates and infants: mostly supratentorial: teratoma, primitive neuroectodermal tumour, high-grade astrocytoma, choroid plexus papilloma (causes hydrocephalus by overproduction of CSF).

Non-tumour SOLs important in Pakistan

Quick revision

• Metastasis = commonest; lung > breast > melanoma/kidney.
• Glioblastoma = commonest primary malignant; resection + radiotherapy + temozolomide; about a year median.
• Triad: seizures, raised ICP, progressive focal deficit.
• Dexamethasone + PPI for oedema; antiepileptics only after a seizure.
• Meningioma: dural-based, uniform enhancement, benign, often curable.
• Pituitary: micro < 10 mm, macro > 10 mm; prolactinoma → cabergoline; trans-sphenoidal surgery; watch for DI.
• Acoustic neuroma: CPA, unilateral deafness, NF2 if bilateral.
• Children: medulloblastoma, ependymoma, pilocytic astrocytoma in the posterior fossa.
• In Pakistan, always think of tuberculoma, cysticercosis and abscess in a ring lesion.

Written by The House Job from standard references (Bailey & Love; Kumar and Clark's Clinical Medicine).

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