Neuro-oncology and neurological manifestations of systemic disease
Brain tumour questions test the pattern of common tumours, the 2021 WHO classification, emergency management of raised intracranial pressure and cord compression, and the neurological consequences of systemic illness and cancer.
Primary and secondary tumours
Metastases are the commonest adult brain tumours: multiple lesions at the grey-white junction, ring enhancement, marked oedema. Common primaries are lung, breast, melanoma, renal and colorectal. Meningioma is extra-axial, homogeneously enhancing with a dural tail. Glioblastoma is a thick, irregular, ring-enhancing intra-axial lesion crossing the corpus callosum with central necrosis; under the 2021 WHO classification, IDH-wildtype astrocytoma with TERT promoter mutation, EGFR amplification or +7/-10 copy number change is graded 4 even without microvascular proliferation or necrosis. IDH-mutant, 1p/19q-codeleted tumours are oligodendrogliomas and behave better. Vestibular schwannoma presents with unilateral sensorineural hearing loss and arises in the cerebellopontine angle (bilateral in neurofibromatosis type 2). Pituitary adenoma causes bitemporal hemianopia and endocrine syndromes; craniopharyngioma calcifies. Medulloblastoma is a posterior fossa tumour of childhood.
Emergencies
Raised intracranial pressure: headache, vomiting, papilloedema, reduced consciousness, Cushing response. Give dexamethasone for tumour oedema with a neurosurgical plan; avoid lumbar puncture when there is a mass. Spinal cord compression from metastatic disease requires whole-spine MRI, dexamethasone 16 mg daily, and surgery or radiotherapy within 24 hours - outcome depends on pretreatment ambulation.
Systemic disease
Paraneoplastic syndromes: anti-Hu (encephalomyelitis, sensory neuronopathy, small-cell lung cancer), anti-Yo (cerebellar degeneration, breast or ovarian cancer), anti-amphiphysin (stiff-person syndrome), anti-Ri (opsoclonus-myoclonus). Lambert-Eaton syndrome associates with small-cell lung cancer. Diabetes causes distal symmetrical neuropathy, mononeuropathies and hypoglycaemic coma. Uraemia and hepatic failure cause encephalopathy and asterixis. Hyponatraemia corrected too quickly causes osmotic demyelination. B12 deficiency causes subacute combined degeneration and macrocytic anaemia. Sarcoidosis causes cranial neuropathy and basal meningeal enhancement.
Worked example
A 60-year-old with known prostate cancer develops band-like thoracic pain, leg weakness and urinary retention over two days. Give dexamethasone 16 mg immediately, image the whole spine with MRI the same day, and refer for surgical decompression or radiotherapy. Do not wait for plain films, which are insensitive.
Traps
Seizure prophylaxis is not routine after brain tumour diagnosis. Steroids given before biopsy can obscure lymphoma. Not all ring-enhancing lesions are metastases - abscess and glioma mimic them. Cord compression can occur without back pain and requires whole-spine imaging because of multiple levels.