The most common type of benign and intracranial tumor are meningiomas. They come from arachnoid cap cells. Arachnoid cap cells are inside a thin, web-like membrane that covers the brain and spinal cord. The arachnoid makes up one of the three protective layers which surround the brain and the spinal cord called the meninges. The dura mater and pia mater are the other two layers of the meninges. Most meningiomas are not malignant but they can continue to grow at a slow pace until they are really large. This can make them life threatening. Some types of meningiomas can be very aggressive and sometimes patients can have several tumors at the same time.
Some meningiomas are located along the dural lining in the venous sinuses of the brain and base of the skull. This is where arachnoid cap cells are most active. Here are subtypes that are based on the location of the tumor.
- Cavernous Sinus Meningioma: Near the area that drains deoxygenated blood to the heart from the brain
- Cerebellopontine Angle Meningioma: Near the margin of the cerebellum
- Cerebral convexity Meningioma: Near the upper surface of the cerebral convexity
- Foramen Magnum Meningioma: Near the base of the skull opening where the lower part of the brainstem passes
- Intraorbital Meningioma: in or around the eye sockets
- Intraventricular Meningioma: In the fluid chambers that carry and make CSF in the brain
- Olfactory Groove Meningioma: on the nerves that connect the nose to the brain
- Parasagittal/Falx Meningioma: Adjacent to the dural fold that separates the two hemispheres of the brain
- Petrous Ridge Meningioma: Portion of the temporal bone that has sections of organs that deal with hearing
- Posterior Fossa Meningioma: Near the back of the brain
- Sphenoid Meningioma: Near the sphenoid bone behind the eyes
- Spinal Meningioma: In the spine or against the spinal cord
- Suprasellar Meningioma: Near the area of the skull where the pituitary gland is
- Tentorium Meningioma: Near where the brain connects with the brainstem
TYPES AND CLASSIFICATIONS
The World Health Organization (WHO) has a frequently used classification of brain tumors. The WHO has 15 variations of meningiomas listed according to their cell type. These are meningioma subtypes. The subtypes are divided into three grades that focus on how fast it grows and how likely it is to recur based on cell features.
- WHO Grade I: Benign; meningothelial, fibrous, transitional, psammomatous, angiomatous, microcystic, secretory, lymphoplasmacytic-rich, metaplastic
- WHO Grade II; Atypical; Chordoid, Clear Cell, Atypical
- WHO Grade III: Malignant; Papillary, Rhabdoid, Anaplastic
Atypical meningiomas are called grade II and make up around 18% of cases. They show unusual cell features and increase of tissue. They grow fast and have a key feature of a brain invasion. Atypical meningiomas are more likely to recur than grade I meningiomas.
Malignant meningiomas are grade III. They show many cell abnormalities and grow very fast. They can likely invade the brain and recur.
PREVALENCE AND INCIDENCE
The Central Brain Tumor Registry of the United States Statistical Report shows that from 2012-2016 tumors diagnosed in the United States that meningiomas were the most common with around 37.6% of all primary central nervous system tumors with 33,560 cases reported in 2019. 8.6 per 100,000 people have a meningioma incidence of all main brain and spinal cord tumors. As age increases, so does the incidence of meningiomas. The main age to get meningiomas is around 66 years old/ Most meningiomas are benign and only 1.7% are malignant, grade III tumors.
The risk of getting a meningiomas will increase with age showing significant increase over the age of 65. Ages 0-14 have the least risk of meningiomas. It is seen that African Americans have more risk of getting meningiomas than other ethnic groups.
High doses and exposure to ionizing radiation has been shown to increase risk of brain tumors such as meningiomas. There is also a linkage between low doses of radiation and the presence of a meningioma. Dental X-rays have exposure to ionizing radiation. Full mouth dental radiographs have been seen to increase risk for meningiomas. Neurofibromatosis type 2 is a genetic disorder that may increase a person’s risk of getting a meningioma and more aggressive meningiomas.
Brain Science Foundation has listed studies that show a relationship between meningiomas and hormones:
- Post-pubertal women have more risk of getting meningiomas than men
- More females get meningiomas than men during the years of reproduction
- Estrogen, progesterone and androgen are often present in meningiomas
- There is a relationship between breast cancer and meningioma
- There is a relationship between menstruation, pregnancy, and meningiomas
Oral contraceptives and hormone replacement therapy may increase the risk of having a meningioma.
There may be a relationship between obesity and the development of meningiomas.
Once meningiomas are larger in size, symptoms become more obvious. Some meningiomas may not present any symptoms at all. Some symptoms include:
- Personality change
- Pregressive focal neurologic deficit
- Being drowsy
- Weakening in the muscles
- Visual impairment
Symptoms are usually related to the location of the tumor:
- Falx and Parasagittal: brain functioning impairment, reasoning and memory impairment. Leg weakness or numbness and possibly seizures
- Convexity: Can lead to headaches, seizures, neurologic issues
- Sphenoid: Problems visually, sensation loss in face, seizures
- Olfactory Groove: Smell loss as nerves are compressed. Vision impairment if optic nerve is compressed
- Suprasellar: visual impairments
- Posterior Fossa: Symptoms related to the face, hearing loss, unsteady walking, coordination issues
- Intraventricular: Can block CSF flow, headaches, hydrocephalus, mental impairments
- Intraorbital: Increase of pressure in eyes, vision impairment
- Spinal: back pain
Most meningiomas grow slowly and the symptoms may be very discrete. This can make them hard to diagnose. The symptoms of meningiomas can also relate to many other health issues.
If a patient has progressive mental impairments, seizures, or headaches, intracranial pressure, then a neurological evaluation should be done.
Imaging can help with the diagnosis. This can include CT scans or an MRI. An intraoperative MRI can be used to help with tumor removal. MRS can be used to look at the chemicals in the tumor.
A biopsy can help diagnose meningiomas. The neurosurgeon will get tissue to examine and work with a pathologist to come to a diagnosis and learn more about the tumor.
Meningiomas have a well defined border and this allows for complete removal of the tumor. This is the best chance to be cured. The neurosurgeon will perform a craniotomy to be able to access the tumor. The surgeon will work to remove as much of the tumor as possible. Complete removal is not always possible and can be very risky.
The surgeon will work to save the patient's neurological function over resecting the whole tumor. Sometimes a full tumor removal can cause death and it may be better to not remove the whole tumor. Preoperative embolization can help increase safety during the surgery. This is where the surgeon adds a compound to the blood vessels to fill them and stop the supply of blood to the tumor.
Observation over a certain time period can help with patients who:
- Have few symptoms and little swelling of the brain
- Have mild symptoms with a history of tumors that do not affect daily living
- Slow symptom progression in older patients
- If treatment has too great of a risk
- Do not want to have surgery
Radiation therapy uses high energy x-rays to destroy cancer cells or unusual cells and to make tumors smaller. If the tumor cannot be operated on, this is another option.
- Standard external beam radiotherapy: using multiple radiation beams to cover the tumor and limit the dose to nearby areas. The risk over time of radiation is low. New techniques include 3DCRT, and intensity-modulated radiotherapy.
- A certain type of radiation where protons are directed at the tumor. Less tissue around the tumor will be damaged.
- Stereotactic radiosurgery: puts radiation with multiple beams to tumor tissues. Less damage will be made to nearby tissues.
This treatment is rarely used as treatment. This might be used in malignant types than cannot be treated with normal treatment options.
The outcome can best be predicted by the patient's age. The younger the patient is, the more likely the outcome. If the tumor can be removed surgically, the more likely the outcome.
Central Brain Tumor Registry of the United States Statistical Report shows that there is an 84% chance of ten year survival from a benign meningioma. There is a 62% chance of ten year survival for those with malignant meningiomas. Spine benign meningiomas have a 96% ten year survival compared to 86% ten year survival of cerebral meningiomas. Malignant spinal meningiomas have a higher rate of ten year survival (73%) than malignant brain meningiomas (55.7%).