Meningioma is the most common form of malignancy in the central nervous system. It is a mesenchymal tumour that arises from the meninges.
The most common form is meningioma, grade I. More aggressive types, namely atypical meningioma and anaplastic meningioma, also exist and have a worse prognosis.
Meningioma is more common in women; although it can occur at any age it is most common in the 50s.
The exact aetiology is not known, but risk factors include:
- Exposure to ionising radiation - the increased use of CT brains is thought to have increased the numbers of meningiomas
- Genetic susceptibility - neurofibromatosis type II is the most commonly associated genetic syndrome, where patients also develop numerous schwannomas.
Clinical Features & Natural History
Clinical features relate to the site of disease and the size and invasion of the tumour. They often include headache, seizures, visual disturbance, ataxia or weakness.
On imaging, menginiomas are typically enhancing with a dural tail.
Meningiomas can have several histological patterns - only the chordoid, clear cell, rhabdoid and papillary types upstage the tumour to grade II or III. The common forms are:
- Meningothelial meningioma - consists of epithelioid cells with pink cytoplasm and indistinct borders arranged into lobules
- Fibrous meningioma - consists of spindle cells arranged in a whorled pattern
- Transitional meningioma - consists of both types
Any type may have psammamoma bodies and calcification. Brain invasion is not seen. Invasion of bone through vascular cannaliculi is not considered bone invasion.
Atypical meningiomas are classified by either:
- Combination of 3 or more of increased mitotic count (4-20 per 10 hpf), increased cellularity, patchy areas of necrosis, or sheet like growth pattern.
- Clear cell histology
- Chordoid histology resembling chordoma
Invasion of the brain tissue or bone is also associated with atypical meningioma.
Anaplastic meningioma is the rarest form of meningioma (2%) and is associated with a uniformly bad prognosis with 2 year survival of < 50%.
It is classified by:
- High mitotic count (> 20 per 10 hpf)
- Rhaboid histology
- Papillary histology