Brain metastases

Overview

•Most common intracranial malignancy in adults - approximately 10x more common than primary brain tumours

•Occur in 10-30% of adult cancer patients

•Spread via haematogenous route - preferentially seed the grey-white matter junction (vessels narrow abruptly, trapping tumour emboli)

Presentation

•Headache - classically worse in the morning (raised ICP maximal after recumbency and CO2 retention during sleep)

•Nausea and vomiting - projectile vomiting suggests acute pressure rise

•Focal neurological deficits - hemiparesis, aphasia, visual field defects, cerebellar ataxia, diplopia

•Seizures - new-onset seizures in an older adult with known cancer = brain metastases until proven otherwise

•Cognitive/behavioural change - personality change, memory impairment

•Papilloedema - indicates raised ICP; absence does not exclude metastases

•Cushing's reflex (bradycardia + hypertension) - very late sign of imminent brainstem herniation

🚨

Melanoma, renal cell carcinoma, and choriocarcinoma metastases are particularly prone to intracranial haemorrhage - consider metastatic disease in any patient with a relevant cancer history presenting with apparent haemorrhagic stroke.

Investigations

🏆 Gold standard

•MRI brain with gadolinium contrast - ring-enhancing lesions at grey-white matter junction with disproportionate vasogenic oedema; multiple lesions strongly favour metastases

•First-line (urgent/if MRI unavailable): CT brain with contrast - less sensitive for small/posterior fossa lesions

•CT chest/abdomen/pelvis - identify primary if unknown, stage systemic disease

•Bloods - FBC, U&E, LFTs, calcium (hypercalcaemia of malignancy), LDH, tumour markers

🥈 Second-line

•PET-CT for occult primary; stereotactic biopsy if primary unknown or single lesion indeterminate

🎯

Multiple ring-enhancing lesions at the grey-white matter junction = brain metastases until proven otherwise. A single ring-enhancing lesion has a broader differential: solitary metastasis, high-grade glioma (GBM), brain abscess, tumefactive MS.

Differential Diagnosis

•Primary brain tumour (GBM) - more likely if single lesion, no known primary, lesion crosses corpus callosum

•Brain abscess - ring-enhancing with fever/immunosuppression; restricted diffusion on DWI distinguishes from necrotic metastasis

•Cerebral infarction - acute onset, non-enhancing on early CT

•Tumefactive MS - younger patient, incomplete ring enhancement, other white matter lesions

Management

•Raised ICP/oedema: dexamethasone - vasogenic oedema responds well as it reduces BBB permeability; give with PPI

•Definitive treatment guided by number of lesions, performance status, systemic disease control, and primary histology - MDT (oncology, neurosurgery, neuroradiology)

Complications

•Cerebral herniation - transtentorial or tonsillar; life-threatening uncontrolled raised ICP

•Leptomeningeal disease (carcinomatous meningitis) - headache, cranial nerve palsies, radiculopathy; diagnosed on MRI or CSF cytology; very poor prognosis

•Hydrocephalus - CSF obstruction, especially posterior fossa lesions

•Corticosteroid side effects - hyperglycaemia, proximal myopathy, insomnia from prolonged dexamethasone use

🎯

The spine is the most common site of bone metastases (high red marrow content and venous plexus access), not the skull. Lung, breast, and prostate are the most common primaries causing bone metastases.

Primary Tumours - Most Common Sources

Common primaries causing brain metastases

Lung - most common overall (incl. small cell)

Breast - esp. HER2+ or triple-negative

Melanoma - prone to haemorrhage

Renal cell carcinoma - prone to haemorrhage

Colorectal

Choriocarcinoma - prone to haemorrhage