Tumor Types> Meningiomas
Meningiomas are tumors that arise from the dura. The dura mater is the membrane covering the entire interior of the skull. It also creates compartments within the skull: the falx, which separates the right side of the brain from the left side and the tentorium, which forms the shelf separating the cerebrum from the cerebellum and brainstem. The latter structures are housed in the posterior fossa below the tentorium, termed the infratentorial space.
Dura also encloses a space on the inside of the skull located on each side of the sella where the pituitary gland sits. This space is called the cavernous sinus. The carotid arteries run through here, supplying the front 2/3rds of the brain, a large network of veins which drain the front 2/3rds of the brain and several cranial nerves (associated with muscles for eye movement and sensation from the upper face).
Meningiomas are usually named for the part of the dura they come from. Hence, a meningioma starting in the falx is called a falx meningioma , a meningioma in the tentorium is called a tentorial meningioma , a meningioma in the cavernous sinus is called a cavernous sinus meningioma and so on. Convexity meningiomas are tumors located over the outer surface of the brain, but do not involve the dura covering the sagittal sinus (midline vein). Those that do involve the sagittal sinus are called parasagittal meningiomas.
Some meningiomas are named for the bone which the tumorous dura covers. The sphenoid wings, for example, are bones located behing the eye socket. There are two parts: the greater wing (forming the back of the eye socket) and the lesser wing (forming the back roof of the eye socket). Meningiomas from the dura covering these are called sphenoid meningiomas. The place where the greater and lesser wings meet is called the sphenoid ridge - a favorite spot for meningiomas. Surgeons like to classify sphenoid ridge tumors still further: the lateral third, middle third and medial third of the sphenoid ridge. This is important in assessing surgical risk. Lateral and middle third meningiomas are usually less complicated to remove than medial third meningiomas which are complicated by the juxtaposition of the carotid artery and optic nerve.
Most meningiomas are benign and slow growing and can grow for years without producing any symptoms. When they do produce symptoms, it's due to irritation of compressed brain tissue (seizures), damage to brain tissue (neurological deficit such as paralysis) or elevation of intracranial pressure from the mass of the tumor itself. Olfactory groove meningiomas which grow from beneath both frontal lobes can become very large before a diagnosis is made. The first actual symptoms relate to a loss of the sense of smell which usually goes unnoticed or blamed on allergies.
Malignant Meningiomas
Some meningiomas are more aggressive than others and tend to recur faster. The so-called "atypical meningioma" have mitotic figures and other features suggestive of malignant behavior. Occasionally radiation therapy is recommended for these tumors following surgery. In addition, the so-called hemangiopericytoma can be a bad actor and can recur quickly and even metastasize to other parts of the central nervous system and to other parts of the body.