Meningioma

Meningiomas arise from arachnoid cap cells and are attached to the dura. They are the most common primary intracranial tumour, more frequent in women and with age, and are associated with prior cranial irradiation and neurofibromatosis type 2. The 2021 WHO classification recognises 15 histological subtypes grouped into CNS WHO grades 1, 2 (atypical) and 3 (anaplastic), and includes molecular criteria: TERT promoter mutation or homozygous CDKN2A/B deletion makes a tumour grade 3 regardless of histology^[1]. Brain invasion is a criterion for grade 2. Most meningiomas are grade 1.

Many meningiomas are found incidentally. Symptoms depend on location: seizures and focal deficits with convexity and parasagittal tumours, visual loss with tuberculum, clinoidal and optic-sheath tumours, anosmia and frontal-lobe change with olfactory-groove tumours, cranial-nerve deficits with skull-base and petroclival tumours, and brainstem compression or hydrocephalus with large posterior-fossa tumours.

MRI shows an extra-axial, dural-based mass with homogeneous enhancement, often a dural tail, and a CSF cleft separating it from brain. CT shows calcification and hyperostosis of adjacent bone. Peritumoural oedema suggests pial blood supply and a more difficult brain–tumour plane. CT or MR venography assesses involvement of the venous sinuses, and catheter angiography is used selectively for vascular anatomy or preoperative embolisation. Somatostatin-receptor PET (DOTATATE) can help define tumour extent and distinguish residual tumour from scar.

The EANO guideline recommends observation with serial MRI for small, asymptomatic tumours, and surgery as the main treatment for symptomatic or growing tumours when they can be removed safely; radiosurgery is an alternative for small tumours, and radiotherapy is used for residual or recurrent tumour and for higher-grade disease^[2]. Factors that favour surgery include symptoms, growth, peritumoural oedema, younger age and an accessible location.

The Simpson grade describes the completeness of removal^[3]:

• Grade I: macroscopically complete removal with excision of the dural attachment and any abnormal bone.
• Grade II: complete removal with coagulation of the dural attachment.
• Grade III: complete removal without resection or coagulation of the dural attachment or extradural extension.
• Grade IV: subtotal removal.
• Grade V: decompression with or without biopsy.

Simpson's original series linked higher grades to more recurrence. In the modern era, with MRI follow-up and radiosurgery for residual disease, the difference in recurrence between Simpson grade I and the lower grades of resection for WHO grade 1 tumours is smaller than once thought, supporting a less aggressive strategy where radical removal would risk neurological injury^[4].

• Devascularise early: detach the tumour from its dural base (the “four Ds”: devascularise, detach, debulk, dissect).
• Debulk internally with an ultrasonic aspirator before dissecting the capsule from brain, preserving the arachnoid plane and the cortical veins.
• Keep the encased arteries and cranial nerves in view; leave tumour on them rather than injuring them.
• Patent major sinuses invaded by tumour are usually not resected; residual is followed or irradiated. Sinus resection and reconstruction is reserved for selected patients in experienced hands^[5].
• Drill hyperostotic bone and excise the involved dura with a margin where safe; reconstruct the dura watertight.

Grade 1 meningiomas removed completely have low recurrence rates, while atypical and anaplastic tumours recur frequently and are usually treated with adjuvant radiotherapy. Postoperative function depends mostly on location and preoperative status; skull-base tumours carry the highest risk of cranial-nerve deficits. Long-term imaging follow-up is required because recurrences can appear many years later^[2].