Tumors of the meninges

Meningiomas represent the second most common central nervous system neoplasm in adults and account for 30% of all primary brain tumors. The incidence of meningioma is 4.7 cases per 100. 000 person-years, and women outnumber men by 2:1. The incidence of meningioma increases with increasing age, and the median age at diagnosis is 63 years. The most common locations for intracranial meningiomas are parasagittal, sphenoid ridge, and convexity. Meningiomas arise from the meningothelial cells of the arachnoid layer forming the external lining of the brain. The World Health Organization (WHO) has classified meningiomas into three grades: benign (WHO grade I), atypical (WHO grade II), and anaplastic or malignant (WHO grade III). Benign meningiomas are those with a low risk of recurrence or aggressive growth. Conversely, grade II and grade III meningiomas possess a greater likelihood of recurrence or aggressive growth. The most common genetic alteration in meningiomas is monosomy of chromosome 22. Some 40-70% of meningiomas exhibit loss of heterozygosity for markers from the chromosomal region 22q12.2 that encompasses the NF2 gene. Mutations specifically in the NF2 gene have been reported in 30-60% of sporadic meningiomas. Complete surgical excision is the treatment of choice for meningiomas. Radiation therapy has evolved as an additional means for controlling meningioma in patients who have undergone a subtotal resection or who have tumors with atypical or anaplastic histologies. No clear evidence of efficacy has been shown for chemotherapeutic agents, although a number of different agents have been investigated. Hemangiopericytomas comprise approximately 1% of intracranial neoplasms. Their clinical presentation, imaging, and intraoperative findings may be indistinguishable from those of meningiomas. Most patients with hemangiopericytomas have been symptomatic for less than 1 year, reflecting the more aggressive clinical course of this tumor. Surgical resection is the primary treatment for this tumor. Preoperative embolization can aid in reducing operative blood loss. Postoperative radiation therapy is recommended. Recurrence of hemangiopericytoma is the rule, and a high index of suspicion must be maintained with regard to screening for recurrence and distant metastases.