Neuro-oncology (Intracranial and Spinal Tumours)
Expect questions on classification, extent of resection, adjuvant therapy and the sequence of diagnosis before treatment.
Classification and grading
WHO 2021 combines histology with molecular markers. Adult diffuse gliomas are astrocytoma IDH-mutant, grades 2 to 4; oligodendroglioma IDH-mutant and 1p/19q-codeleted, grades 2 to 3; and glioblastoma IDH-wildtype, grade 4. An IDH-wildtype astrocytoma with TERT promoter mutation, EGFR amplification or combined chromosome 7 gain and 10 loss is grade 4 even without necrosis.
Glioma management
- Maximal safe resection improves survival and preserves function; awake craniotomy with cortical and subcortical mapping is used for dominant hemisphere tumours.
- 5-aminolevulinic acid fluorescence helps resection of high-grade glioma and is not used for low-grade tumours.
- Glioblastoma: 60 Gy in 30 fractions with concomitant and adjuvant temozolomide. MGMT promoter methylation predicts greater benefit.
- IDH-mutant lower-grade glioma benefits from radiotherapy plus chemotherapy after resection.
- Dexamethasone at the lowest effective dose controls oedema; it is not antitumour therapy.
Extrinsic tumours and others
- Meningioma: Simpson grade predicts recurrence; WHO grade 2 or 3 warrants adjuvant radiotherapy. Small asymptomatic lesions in the elderly may be observed.
- Vestibular schwannoma: Koos grading; observe, radiosurgery for lesions up to about 3 cm, or microsurgery with facial nerve preservation graded by House-Brackmann.
- Pituitary adenoma: prolactinoma is treated first with a dopamine agonist; others by transsphenoidal surgery. Apoplexy is an emergency.
- Primary CNS lymphoma: biopsy first, because steroids can melt the tumour and destroy the diagnosis; high-dose methotrexate is the backbone.
- Brain metastases: graded prognostic assessment; stereotactic radiosurgery for a limited number of lesions; hippocampal-sparing whole brain radiotherapy when whole brain treatment is needed.
- Spinal tumours: extradural metastases commonest, then intradural extramedullary meningioma and schwannoma, then intramedullary ependymoma and astrocytoma.
Worked example
A 35-year-old has a seizure and a non-enhancing frontal lesion with an IDH mutation and no necrosis or microvascular proliferation. This is an IDH-mutant astrocytoma, grade 2. Plan maximal safe resection with mapping, then discuss radiotherapy and chemotherapy; do not label it glioblastoma.
Traps
- Giving steroids before biopsy in suspected lymphoma.
- Confusing Simpson grade with WHO grade.
- Omitting the molecular report from the diagnosis.
- Using 5-ALA for a presumed low-grade tumour.