A meningioma is a tumor that arises from the lining of the brain and/or spinal cord (ie: the "meninges"). They arise from cells known as "arachnoid cap cells". Meningiomas are usually slow growing, "benign" tumors, which means that they are not usually considered cancerous.
When viewed under the light microscope, meningiomas can have many different appearances. The most common type is a dense sheet-like formation of cells interspersed with closely packed blood vessels. Sometimes the sheets of cells can be separated by connective tissue.
Frequently, meningiomas will have calcium deposits in them known as "psammoma bodies". Uncommonly, meningioma cells may take on a malignant appearance characterized by increased cellular division (ie: "mitotic figures") and invasion of the tumor cells into surrounding brain or bone.
Meningiomas test positive for epithelial membrane antigen (EMA) and vimentin (a marker of connective tissue). Ki-67 (a marker of proliferation) can be elevated in more aggressively behaving tumors.
The most common genetic abnormality seen in patients with meningiomas is found on chromosome 22. If present, a mutation in the NF2 gene on this chromosome causes type 2 neurofibromatosis; this disease predisposes individuals to developing multiple tumors including meningiomas. Other less common genetic abnormalities can be seen on other chromosomes as well.
Due to their slow growing and benign nature, many meningiomas cause no symptoms. However, if they become too large or start to compress adjacent brain tissue they can cause headache, seizures, confusion, or visual problems.
The most common location for a meningioma is in between the two hemispheres of the brain - the so called "parasagittal" location. Parasagittal meningiomas near the portion of the brain responsible for muscle movements may cause weakness in the opposite leg.
Diagnosis of meningioma can reliably be made based on characteristic findings on CT or MRI scans. Interestingly, many meningiomas are found incidentally when a CT or MRI is done for other reasons.
However, like any other tumor, meningiomas can only be truly diagnosed once a specimen is sent to the pathology lab for analysis. Pathologists can reliably make the diagnosis based on typical histological features.
Meningiomas must be distinguished from a more malignant tumor known as a hemangiopericytoma. Hemangiopericytomas can look similar to meningiomas on imaging studies.
Many meningiomas can be watched over time with repeat imaging studies; this is especially true if they are small and not causing neurological signs or symptoms.
On the other hand, large or symptomatic meningiomas require surgical resection. Many meningiomas can be removed completely without any significant problems. However, some meningiomas may be near vital structures such as the venous draining systems of the brain (ie: "venous sinuses") where complete surgical removal may be impossible, or extremely difficult. In these cases the tumor is debulked as much as possible. The residual tumor can be followed and/or irradiated with repeat imaging to assess for enlargement.
Residual tumor after incomplete surgical resection, or meningiomas in difficult to access locations are candidates for radiation therapy. Several studies have shown that radiation decreases the growth rate of meningiomas.
Meningiomas are considered "benign" tumors of the brain. They arise from arachnoid cap cells, which are located in a layer of the meninges (ie: the covering of the brain) known as the arachnoid. Symptoms include headache, weakness, vision problems, paresthesias (ie: abnormal sensations), amongst many other possible symptoms. Diagnosis can be made reliably from imaging studies such as CT or MRI. If symptomatic, or large, treatment is surgical resection. Small asymptomatic meningiomas can be managed with repeat imaging to assess for growth over time.
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