Meningioma

Introduction

A meningioma is a non-glial cell growth arising from the arachnoid meningothelial cells within the meninges. Meningiomas form around 30% of all brain tumours.

Meningiomas are typically benign and slow growing. Around 90% of meningiomas occur within the cranium, with 25% around the falx cerebri, 20% on the convexity, and 20% on the sphenoid wing.

The annual incidence of meningiomas is currently around 1.3-7.8 per 100,000 and are more common in females than males.

Mysid / Public domain

Figure 1 – Coronal section of the skull, meninges, and cerebrum

Classification

The WHO classification of meningiomas classifies them into 3 grades

Risk Factors

Most cases are sporadic with no identifiable risk factors. However, known risk factors include increasing age, previous cranial irradiation, or certain genetic disorders (e.g. neurofibromatosis type II).

Clinical Features

Meningioma presentation occurs as that of any space-occupying lesion. They can also often be an incidental finding, especially when asymptomatic and benign.

Clinical features can include seizures, cranial nerve palsies or visual field defects, language dysfunction, or features of raised intracranial pressure.

Differential Diagnosis

Potential differentials can be either neoplastic or non-neoplastic lesions. Neoplastic lesions include gliomas, secondary metastasis, or lymphoma, whilst non-neoplastic causes of a mass lesion include infection (i.e. cerebral abscess) or infarction.

Investigations

Imaging

CT head imaging with IV contrast is often the first line investigation performed. Meningiomas appear as well-circumscribed (globose) extra-axial masses with uniform contrast enhancement on imaging, and potential associated regions of dural thickening.

MRI imaging may also be used to further characterise and assess the lesion. Angiography can be required the assessment of tumour blood supply to aid in planned operative approach.

Adapted from James Heilman, MD [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)] and Hellerhoff [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]

Figure 2 (A) CT scan showing a meningioma with surrounding oedema (B) MRI scan showing a meningioma

Biopsy

A biopsy can be used to confirm the diagnosis, which can be achieved either through a stereotactic (burr hole) approach or through open exploration (craniotomy).

For the burr hole approach, a Leksell stereotactic frame can be used, which is based around an arc on a rectangular based ring attached to skull via four pins. The system then co-ordinates the centre of the target to perform the biopsy (can also be used in gamma knife surgery, discussed later).

Management

Treatment choice depends on patient factors (e.g. age, co-morbidities, performance status), disease factors (e.g. volume, location, evidence of growth, evidence of calcification), and treatment factors (e.g. probability of satisfactory excision or disease control, operative risks)

Treatment options involve combinations of endovascular embolisation, surgical removal, radiotherapy (including gamma knife). Chemotherapy will be employed as adjuvant treatment to surgery, or in anaplastic or recurring meninigiomas.

Endovascular Embolisation

This treatment is usually performed by an interventional neuroradiologist*, involving an endovascular catheter passing up to the location of the meningioma, before embolising the tumour.

This technique can act as an adjuvant to neurosurgical resection, aiming to optimise chance of resection success (minimising bleeding in highly vascularised tumours), improve operating times and recovery times, or even to facilitate palliation 

*Intraoperative digital subtraction angiography can be used to ascertain the correct position of the vasculature being targeted

Surgical Removal

There are 3 classifications for extent of resection (EOR) that can be performed (1) gross total resection* (2) subtotal resection (3) biopsy only.

A Mayfield three-point fixation method is often employed for accuracy in targeting the lesion; a Mayfield clamp is used to immobilise the patient’s skull, the image-guided system and retractor components can then be attached to the clamp.

The location of the meningioma using navigation is confirmed using surface anatomical landmarks. The operative approach chosen aims to maximise conservation of normal anatomy and lesion exposure.

*Whilst the entire tumour removed, microscopic cells may remain

Radiotherapy

By NRC [Public domain]

Figure 3 – Graphic demonstrating the Leksell Gamma Knife

Radiotherapy can be employed as an adjunct to surgery, in cases of tumour recurrence, or where factors preclude surgery.

Stereotactic Radiosurgery (SRS) uses high-dose focused radiation that targets the lesion and minimises damage to surrounding tissues, even allowing long-term tumour control to be possible.

One such type of SRS is the Gamme Knife, using multiple beams of radiation from all three dimensions to focus on a small volume, allowing for high radiation doses to be delivered.

Prognosis

The Simpson grade of meningioma resection can be used to help predict symptomatic recurrence following treatment (although other factors can now also employed to determine mortality)