Meningioma

About meningiomas 

Meningiomas are almost always benign (non-cancerous) tumours, normally arising from the coverings (meninges) of the brain and spine, although rarely they can also arise within the fluid spaces inside the brain (ventricles). They usually grow quite slowly, around 1-2mm each year in diameter, although this is variable. They have been known to grow rapidly during pregnancy, probably driven by the increased levels of the hormones progesterone and oestrogen. There are many different microscopic tumour patterns recognised if these tumours are removed and analysed by pathologists, but the important distinction relates to the ‘grade’ of the tumour, which relates to the risk of recurrence and speed of growth.

• Grade I tumours (the vast majority) typically grow slowly and are cured by complete surgical removal, with only a very small risk of recurrence.
• Grade II tumours are more rapidly growing but still benign. These have a greater risk of recurrence even if apparently completely removed at surgery. Sometimes radiotherapy is recommended to reduce that risk.
• Grade III tumours are thankfully rare, but are aggressive, malignant tumours with a very rapid growth rate. Although these can be removed, they invariably recur and as yet are not curable.

Types of meningioma

Subfrontal meningioma

These are located under the frontal lobes of the brain, on the skull base. When small, these are associated with very little risk of adverse events after radiation treatment, but if larger there can be swelling provoked in the frontal lobes. If extreme this can lead to headaches and even personality change. Large subfrontal tumours are usually removed surgically to avoid these problems.

Para-optic meningioma

As the name suggests these tumours are close to the optic nerves and pathways. There are several subdivisions with regard to exact location, but in principle the risk is that vision will be disturbed as a result of radiation damage to the nerves (RION or radiation induced optic neuropathy). There are ways to reduce the risk of this during the radiosurgery planning and your consultant will make you fully aware of the extent of the risk before any treatment.

Cavernous sinus meningioma

The cavernous sinus is a blood-filled space enclosed by tough membranes on either side of the pituitary gland at the skull base. In addition to blood vessels, the cavernous sinus contains the nerves responsible for eye movements (III, IV and VI) and is very closely related to the nerve giving feeling to the face (trigeminal - V). These tumours often present with a combination of pain behind the eye, a bulging eye (proptosis), a droopy eyelid (ptosis) and double vision due to impairment of the function of the eye movement nerves. Even though these tumours respond well to the radiosurgery, these symptoms do not necessarily improve due to the damage already done to the nerves. Pain often improves – but may transiently increase due to inflammation at the site of treatment. Double vision may also improve, but if it does it often requires many months or years to happen.

Convexity meningiomas

This term is used for any tumour arising from the coverings of the surface of the brain, away from the skull base. They are in contact with and often compressing the brain surface. Usually these can be safely removed surgically, with little risk, but patients with small tumours who are otherwise not fit for surgery (or unwilling to undergo an operation) may be suitable for radiosurgery. The main risk of the treatment in this location is brain swelling related to the injury caused to the tumour and this can also cause epileptic seizures. If it occurs, the swelling normally commences around 3-6 months after treatment and usually disappears again within one year.

Parasagittal meningiomas

There is a central tough membrane dividing the two halves of the brain known as the falx. At the top of this membrane is the major draining vein for the brain (the sagittal sinus). Tumours arising either side of the sagittal sinus are called parasagittal. Surgically their management is complicated by the presence of this large vein, which if damaged can lead to a severe stroke or death. Before radiosurgery was more widely available, complex operations to reconstruct the vein were performed, with high risks to the patient. The current surgical approach is to remove as much tumour as possible without injury to the vein, treating anyremaining tumour with radiosurgery. When these tumours arise close to the part of the brain controlling leg movements, there can be persistent numbness or weakness of the leg (normally on the opposite side to the tumour) after treatment.

Petro-clival meningiomas

This anatomical region is at the base of the brain, in front of the brainstem. These tumours often cause some facial numbness and double vision due to nerve compression. They may also cause balance problems from pressure on the brain stem. Radiosurgery is often the safest form of treatment for these, due to the risks of additional nerve and brain injury from the difficult surgical approach needed to remove them. Size here is crucial and if the tumour is too large, surgery may be the only option, with the aim often being to remove as much of the tumour as possible, leaving a suitable target for radiation. Sometimes with large tumours, an alternative to surgery is to divide the radiosurgery into 3 – 5 ‘fractions’ delivered on consecutive days. This may be less damaging to the surrounding brain, but the longer term results in respect of tumour control are not yet clear.

Cerebello-pontine angle meningiomas

These also occur in the space between the brainstem, hind brain (cerebellum) and the bone encasing the inner ear (petrous bone).