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VII./4.1.: Epidemiology, etiology
Meningiomas are the most common central nervous system neoplasms, account for 13-26% of the primary intracranial tumors (4.3% in childhood, 30% in adulthood, 40% in elderly). The numerous WHO grade I histological subtypes are heterogeneous, but have no influence on the prognosis. WHO grade II meningiomas are atypical, WHO grade III meningiomas are malignant (anaplastic).
Meningiomas frequently found incidentally with neuroimaging or autopsy („incidentaloma”), which alters epidemiology. Prevalence may be around 2.8% in women. Interestingly, meningiomas afflict more often women then men (female-to-male ratio is 2:1); the greatest difference found in the subgroup of 35-44 years of age with female-to-male ratio of 3.15:1. In some subgroups, for example in the cases of thoracic spine meningiomas, the ratio is 9:1.
In prepuberty, incidence does not altered by gender, while atypical and malignant meningiomas (account for 5% of all meningiomas) found slightly more frequent in male. The incidence increases with age, incidence rate is the highest in the 6th and 7th decade. According to the data of the Central Brain Tumor Registry of the United States, the incidence rate of the meningiomas continuously increase in the past decades, but more accurate diagnostic methods and report could alter them.
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Genetics. Despite of meningiomas are benign in the 95% of the cases, genetic analysis prove clonal origin (spawn of one cell). The origin of the tumor is a so called „cap cell” of the aranchnoid granulation, with their active metabolism taking part in cerebrospinal fluid resorption. Chromosome aberrations found in sporadic meningiomas frequently, for example in one third of the cases chromosome 22 NF2 locus (so called merlin) deletion detected, but 14q, 1p, 6q, 18q deletions are well-known as well. Meningiomas occur in certain familiar tumor syndromes (e.g. Gorlin, Cowden, Li-Fraumeni, Turcot, von Hippel-Lindau).
Neurofibromatosis and meningiomas. Neurofibromatosis type 2 (NF2) is a dominantly inherited syndrome with multiple neoplasms. Its genetic background is the NF2 tumorsupressor gene inactivation because of mutation in the chromosome 22 locus q12. NF2 is a rare disorder, with the incidence of 1/33,000. Multiple benign tumors e.g. schwannomas, meningiomas and ependymomas diagnosed frequently in NF2 patients. In half of the patient’s accumulation in the family is not characteristic, in these cases de novo mutations of the NF2 gene detected. Bilateral accustic schwannoma raises the suspicion of NF2, positive result expected in half of the patients. NF2 may be present is 90% of spinal tumors. Half of the NF2 positive patients will have menigioma; the rate is 83% in childhood cases.
Risk factors. Ionising radiation is a definite risk factor. Among the Japanese survivors of the atomic bomb, incidence of meningiomas increased, but the role of lower level doses is also generally accepted. Irradiated patients because of tinea capitis have ten-fold risk of meningiomas (Israel, between 1948 and 1960); total ontoradiograp and irradiation of the skull because of intracranial tumors also increase the risk. Role of the electromagnetic radiation became interesting with the excessive use of mobile phones, but current research did not prove increased risk. E.g. ionising radiation increases meningioma risk with a 17-36 years latency, which means, that results of mobile phone usage are hard to interpret yet.
The clear female dominance proves hormonal risk factors. In most meningiomas, oestrogen and progesterone receptors detected; and in a few cases, meningiomas have a chance to grow in pregnancy or in the luteal phase of menstrual cycle as well. Epidemiology refers to increased risk of meningiomas with hormon replacement therapy, oral anticoncipient use and patients with breast cancer.
Skull trauma could increase risk of meningiomas by traditional point of view, but on the bases of case reports and small case series in which meningioma arise near to the location of a previous skull fracture. No connection confirmed in head injuries and meningiomas in large case series.
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