Neurooncology and neuroinfectology
This domain tests the classification and imaging behaviour of brain tumours, the interpretation of CSF in infection, and the emergency management of raised intracranial pressure and CNS infection.
Tumours (WHO 2021)
Adult diffuse gliomas are classified by IDH status. IDH-mutant with 1p/19q codeletion is oligodendroglioma (grade 2 or 3); IDH-mutant without codeletion is astrocytoma; IDH-wildtype diffuse astrocytic tumour with TERT promoter mutation, EGFR amplification or +7/−10 is glioblastoma, grade 4. MGMT promoter methylation predicts temozolomide benefit. Standard treatment is maximal safe resection followed by radiotherapy 60 Gy in 30 fractions with concomitant and adjuvant temozolomide (Stupp protocol).
Other tumours
Metastases are the commonest adult brain tumours, at the grey–white junction, often multiple; treat with surgery, stereotactic radiosurgery or whole-brain radiotherapy, and use dexamethasone for oedema. Prophylactic antiseizure drugs are not indicated. Meningioma is extra-axial with a dural tail and homogeneous enhancement. Primary CNS lymphoma is periventricular, homogeneously enhancing, and steroids should be avoided before biopsy; treat with high-dose methotrexate. Pituitary adenoma causes bitemporal hemianopia; prolactinoma responds to dopamine agonists. Vestibular schwannoma arises in the cerebellopontine angle and is bilateral in neurofibromatosis type 2. Distinguish pseudoprogression from true progression using RANO criteria.
CNS infection - CSF patterns
- Bacterial meningitis: neutrophils, low glucose (<2.2 mmol/L or CSF/serum ratio <0.4), high protein. Give dexamethasone with or just before the first antibiotic dose in pneumococcal disease; do not delay antibiotics for imaging unless there are focal signs, seizures or immunosuppression - take blood cultures first.
- HSV encephalitis: temporal lobe involvement, acyclovir 10 mg/kg every 8 hours, CSF PCR.
- Tuberculous meningitis: basal exudates, hydrocephalus, low glucose.
- Lyme neuroborreliosis: CSF/serum antibody index, ceftriaxone.
- Neurosyphilis: serology plus CSF; HIV: toxoplasmosis (multiple ring-enhancing lesions), cryptococcus (India ink), PML (JC virus, no enhancement).
- Prion disease: rapidly progressive dementia, myoclonus, cortical ribboning on DWI, positive RT-QuIC.
Worked example
A 62-year-old has headache, fever and neck stiffness. Blood cultures are drawn, dexamethasone and ceftriaxone plus ampicillin are given immediately, and lumbar puncture shows 2,000 neutrophils/µL with glucose 1.5 mmol/L - bacterial meningitis. Do not wait for CT before antibiotics when there are no focal signs.
Traps
Giving steroids before biopsy in suspected lymphoma; using prophylactic antiseizure drugs after tumour surgery routinely; delaying antibiotics for a CT scan; confusing pseudoprogression with progression.