Meningiomas represent approximately 20% of all symptomatic intracranial tumors (DeMonte and Al-Mefty 1995). Meningiomas occur at a rate of 7.8 in 100,000 per year, and only 25% of these (2 in 100,000 per year) are symptomatic on presentation (Radhakrishnan et al 1995). The majority of meningiomas show incidental findings on imaging studies, or are found at autopsy. The male-to-female ratio was 1 to 1.8 for all meningiomas, and 1 to 2.3 for symptomatic meningiomas (Radhakrishnan et al 1995). The incidence of meningiomas increases with age, reaching its peak at the age of 85 years. However, in 1 epidemiologic study, the incidence of symptomatic meningiomas remained relatively unchanged between 40 and 90 years of age. Most other studies report a steady increase in incidence rate of meningiomas after 20 years of age (Cushing and Eisenhardt 1962; MacCarty and Taylor 1979; Rohringer et al 1989). Atypical and anaplastic forms are more common in men (Bollag et al 2010).
Meningiomas have been reported to occur intracranially, as well as spinally ,in association with breast carcinoma and colorectal cancer (Schoenberg et al 1975; Knuckey et al 1989; Malmer et al 2000). Radiation-induced meningiomas arise after low dose radiation, and are often multiple, aggressive, and malignant. They do not have mutations in the 17 exons of the NF2 gene on chromosome 22, in contrast to sporadic meningiomas, where the incidence is 50% (Shoshan et al 2000).
Benign meningiomas have a recurrence rate of 7% to 25%. Satoshi and colleagues investigated histopathologic features that would predict recurrence in grade I meningiomas. This study investigated 135 benign meningiomas, of which 120 were totally resected. Recurrence rate in patients with total removal was 7.5% at 10 years and 9.3% at 20 years. Histopathologic features that were found to be statistically significant and correlated with recurrence include an MIB-1 index of greater than 2%, existence of mitosis, absence of calcification, and a paucity of fibrosis (Nakasu et al 2009).
Atypical meningioma after gross total resection had higher recurrence rates than benign meningiomas. In a large retrospective case series (n=108) done at the University of California, San Francisco, recurrence rates following gross total resection without postoperative radiation was analyzed. Tumor recurrence was 7% at 1 year, 41% at 5 years, and 48% at 10 years. Of these 108 patients, 8 received postoperative radiation without recurrence of tumor. Risk factors for recurrence include older age and histologic changes such as prominent nucleoli and increased mitoses (Aghi et al 2009).
Given that higher grade meningiomas have a high recurrence rate following surgery, researchers have looked into noninvasive methods to predict aggressiveness so as to best tailor individual therapy. In a retrospective multivariate analysis of 378 patients with meningioma at a single institution, it was found that nonskull base location and male sex both have a 2-fold increased risk for grade II/III pathology (Kane et al 2011).
In a retrospective study done by Gabeau-Lacet and colleagues, bone involvement in atypical meningioma and outcome was investigated. This study involved 47 patients with atypical meningioma. Bone involvement was associated with an increased rate of disease progression and decreased survival. It is important to note that 78% of patients with bone involvement at initial diagnosis had tumor recurrent within the bone. This evidence suggests that bone assessment should be undertaken at initial diagnosis of atypical meningioma (Gabeau-Lacet et al 2009).
18F-FDG (F-fluorodeoxyglucose)-PET can be used in the detection of high-grade meningiomas, and some studies indicate that FDG-PET can be used as a predictor of tumor recurrence. Lee and colleagues showed that the tumor-to-gray matter ratio of FDG uptake was significantly increased in high-grade meningiomas versus grade I meningiomas. In this study, it was also illustrated that there is a positive correlation between FDG uptake and high MIB-1 index and mitotic count (Lee JW et al 2009).