Diagnosing symptomatic meningiomas:  Brain MRI (Magnetic Resonance Imaging) is the gold standard for diagnosing intracranial meningiomas.  Usually, when patients develop any neurological symptoms – such as headaches, speech problems, seizures, memory loss, body/extremity numbness or weakness, hearing loss, visual loss, double vision, dizziness, imbalance, etc. – a brain imaging is ordered by the patient’s PCP (primary care physician).  Preferably, when a brain tumor is suspected, MRI with and without Godolinium (contrast injected intravenously) is performed.

When patients have any metal implants in the body such as cardiac pacemaker, MRI cannot be done.  Rather, a brain CT with and without IV contrast is performed.  CT is also done as an adjunct to the brain MRI when the meningioma extends into the surrounding skull or the skull base to better delineate the full extent of the tumor including the extent of bone invasion.

When meningiomas are adjacent to or involving the major venous structures, such as the sagittal sinus, torcular, transverse sinus or sigmoid sinus, MRV (Magnetic Resonance Venogram) may be performed additionally to better assess the full extent of the meningioma’s invasion into the surrounding venous structure(s).

When a very vascular meningioma (i.e. rich in blood supply) is suspected based on the preoperative MR imaging, a cerebral angiography may be performed to visualize the full extent of the blood supply to the meningioma as a part of preoperative planning.  When it would be deemed appropriate and beneficial, at the same time as the cerebral angiography is being done, tumor embolization may be performed to occlude the feeding blood vessels which, in turn, will make the subsequent surgery less bloody and risky.

Diagnosing asymptomatic, or “incidental”, meningiomas:  These days, with the widespread availability and use of brain imaging (either CT or MRI) for evaluating head trauma, nasal sinus complaints or nonspecific neurological complaints, incidental meningiomas (i.e. those detected by an “accident” or not causing any specific symptoms referable to the tumor) are being diagnosed with increasing frequency.  When a non-contrast CT done initially to evaluate nasal sinusitis or minor head trauma, for example, reveals a possible meningioma, a brain MRI with and without Gadolinium is ordered to confirm and better delineate the tumor.

Please see the next section, “Clinical Presentation/Meningiomas by Location”, for examples of meningioma MR images.

Etiology (What’s the cause?) – So far, there are only 2 known definitive factors that lead to meningioma development:  (1) radiation, and (2) the gene associated with Neurofibromatosis type 2 (NF2).  Most likely, meningiomas and other tumors in the brain and the rest of human body develop due to alterations or damages that have occurred in the patient’s gene(s) within certain chromosomes.  Exactly what genes and what kind of alterations or damages lead to meningioma formation are still unknown other than the NF2 gene mentioned above.  However, with the NF2 gene, located on Chromosome 22, the gene defect accounts for a fraction of all (non-NF2) meningioma patients (33%).  Obviously, additional research is required to further elucidate the exact and all genetic changes that lead to meningioma formation.

Additional reading:

Lee JH, Sundaram V, Stein JD, Kinney SE, Stacey DW, Golubic M:  Reduced expression of schwannomin/merlin in human sporadic meningiomas.  Neurosurgery 40:578-587 (1997)

Evans J, Jeun SS, Cowel JK, Harwalkar JA, Golubic M, Lee JH:  Molecular alterations in the NF2 gene and its protein are rarely occurring in meningothelial meningiomas:  J Neurosurgery 94:111-117, 2001

Pathology (What cell type and how aggressive?) – Meningiomas are classified using the World Health Organization (WHO) grading scale, from Grade 1 (benign) to Grade 3 (malignant).  In a single institution review conducted by my group, 92% meningiomas belonged to WHO Grade 1 (benign), while 6% was WHO Grade 2 (aggressive or atypical) and 2% WHO Grade 3 (malignant) meningiomas.  This pathologic classification is critically important in meningiomas because one of the factors that determine how well patients do long-term depends on this tumor “grade”.  For example, only 3% of WHO Grade 1 tumors recur within 5 years of initial surgery, compared to 40% 5-year recurrence rate for WHO Grade 2 tumors, and 80% for WHO Grade 3 meningiomas.

Additional reading:

Meningothelioma as the Predominant Histological Subtype of Midline Skull Base and Spinal Meningioma

Lee JH, Sade B, Choi E, Prayson R, Golubic M:  Meningothelioma as the predominant histologic subtype of midline skull base and spinal meningiomas.  J Neurosurgery 105:60-64, 2006

Prayson R:  Pathology of meningiomas, In: Meningiomas (JH Lee, ed), Springer-Verlag, London, 2008

Definition (What is it?) – Meningiomas are predominantly benign tumors, arising from the covering (“meninges”) of the brain (90%) and spine (10%).  These tumors arise from the arachnoid “cap cells” which are the cells forming the outer lining of the arachnoid layer (the middle of the three meningeal layers).  Strictly speaking, these are not “brain tumors” per se as they do not take their origin from the brain tissue proper.

Epidemiology (How common is it?) – The incidence of symptomatic meningiomas (“how common?”)  is approximately 2/100,000 population per year while the incidence of asymptomatic (tumors causing no symptoms) meningiomas is 5.7/100,000 population per year.  Therefore, the overall combined incidence of all meningiomas (both symptomatic and asymptomatic) is nearly 8/100,000 population/year.  This roughly translates into the yearly incidence of roughly 800 new meningioma patients in a geographic area the size of Los Angeles County which has a total population of 10 million.  Symptomatic meningiomas account for about 15-20% of all primary brain tumors, second most common after glioblastoma multiforme (GBM).  When incidental (i.e. asymptomatic) tumors are included, however, meningiomas account for nearly 60% of all primary brain tumors.  In reality, meningiomas are the most common primary “brain tumors”.

The average age at diagnosis for those requiring surgery, based on the review of my personal operative series of 1200 cases, is 54 years.  For some unknown reason, meningiomas are more common in women by a ratio of 2-2.5:1.

Additional reading:

Meningioma (JH Lee, ed.), Springer-Verlag, London, 2008