Intracranial meningiomas

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Meningiomas are intracranial tumours that develop from the meninges, the membranes that cover the brain and spinal cord. They represent about a third of all the tumours of the brain and the central nervous system. 

Meningiomas are the most frequently diagnosed tumours in people aged 40 to 60 years, and women are twice as likely as men to develop them. In fact, it seems that this type of cancer cells has oestrogen and progesterone receptors.

Meningiomas are usually single, but in some cases the presence of more tumours growing simultaneously has been found in other parts of the brain or spinal cord. Although in most cases intracranial meningiomas are benign and slow-growing (grade I), malignant and recurrent forms have also been found. The latter are aggressive and show a high recurrence rate (grade II) as well as anaplastic forms that are extremely rare and characterised by the development of distant metastases (grade III). These malignant behaviours can be traced back to the site of the tumour, its vascularization or its tendency to local infiltration.

Depending on their location, meningiomas can be classified into several subtypes:

• Cavernous sinus meningioma
• Cerebellopontine angle meningioma
• Cerebral convexity meningioma
• Foramen magnum meningioma
• Intraorbital meningioma
• Intraventricular meningioma
• Olfactory groove meningioma
• Parasagittal/Falx meningioma
• Petrous ridge meningioma
• Posterior fossa meningioma
• Sphenoid meningioma
• Spinal meningioma
• Suprasellar meningioma
• Tentorium meningioma

The World Health Organization (WHO) has classified meningiomas into histological subtypes, that is, based on their cell type.

Benign meningiomas, classified as grade I:

• Meningothelial
• Fibrous (fibroblastic)
• Transitional (mixed)
• Psammomatous
• Angiomatous
• Microcystic
• Secretory
• Lymphoplasmacyte-rich
• Metaplastic

Atypical meningiomas, classified as grade II:

• Chordoid
• Clear cell
• Atypical

Malignant meningiomas, classified as grade III:

• Papillary
• Rhabdoid

•    Anaplastic

Causes of intracranial meningiomas

Although the causes of intracranial meningiomas have not yet perfectly defined, risk factors have been identified that may influence the occurrence of these types of tumours. Meningiomas have been found more frequently in patients who have previously undergone skull radiotherapy, especially the non-fractionated and non-stereotactic type used in the past. In fact, current radiotherapy permits attacking cancer cells in a more defined way, converging radiation at specific points and sparing healthy structures. Numerous studies carried out in the United States have shown that the use of X-rays in the dental field has increased the risk of meningiomas.

Genetic factors can also influence the occurrence of intracranial meningiomas: individuals with neurofibromatosis type 2 (NF2) have been found to have a higher risk of developing this type of tumour, especially malignant and multiple meningiomas.

Symptoms of intracranial meningiomas

As we have previously analysed, intracranial meningiomas are slow-growing tumours. This means that in most cases they are asymptomatic until they reach a large size. That is the reason why, an individual may be aware of having developed this tumour after a CT scan or a magnetic resonance imaging scan of the brain performed for other pathologies.
Symptoms of intracranial meningiomas are due to the compression of lesion onto the nerve structures. Therefore, symptoms may vary depending on the location of the tumour and the type of nervous structure damaged. 
In general terms, symptoms of meningiomas may include:

• Headaches
• Confusion
• Drowsiness
• Muscle weakness
• Visual disturbances, such as diplopia or worsening eyesight
• Speech problems
• Nausea
• Vomiting
• Seizures
• Personality changes, such as apathy, aggression or depression
• Neurological deficits
• Hearing loss or disturbances such as tinnitus
• Dizziness

Diagnosis of intracranial meningiomas

Diagnosing intracranial meningiomas is particularly difficult due to a number of factors. First of all, being a slow-growing tumour, it is often asymptomatic. Furthermore, when symptoms do arise, they individual may attribute them to a normal ageing process, and the doctor to a series of other pathologies. For these reasons, a correct diagnosis of intracranial meningioma could take several years.

In case of suspected meningiomas, an accurate neurological evaluation should be carried out in first place. Subsequently, diagnostic imaging tools must be used:

• CT (computed tomography)
• MRI (magnetic resonance imaging) or NMR (nuclear magnetic resonance)
• Cerebral angiography
• MRS (magnetic resonance spectroscopy)

At present, however, the only way to obtain a true diagnosis is through a biopsy. With it, the doctor can both evaluate whether the tumour is benign or malignant, and classify it accordingly.

Treatment of intracranial meningiomas

Whenever possible, especially for benign meningiomas, neurosurgery is the most suitable treatment to minimise the risks for patients. The most common type of surgery to remove a meningioma is called a craniotomy. The aim is to remove both the main tumour mass and all the parts adhering to the most delicate structures, such as vessels and nerves.

In most cases, however, meningiomas arise at highly critical areas and are particularly vascularized, which makes surgery alone impossible. For patients with meningiomas that cannot be fully removed and in cases of inoperable intracranial meningiomas, hadrontherapy with protons or carbon ions has proven to be particularly effective. This treatment provides optimal long-term control of the disease, causing minimal side effects.

In addition, hadrontherapy has proven to be particularly effective to treatment this kind of tumour in paediatric patients. In fact, this treatment makes it possible to attack only the area affected by the tumour, sparing the surrounding healthy areas, which in children are even more sensitive to radiation.