Histological characteristics of incidentally-found growing meningiomas

Object. With the wider use of CT and MRI, many meningiomas are discovered as incidental findings during diagnostic work-up for unrelated symptoms. The majority shows no or minimal growth. The purpose of this study was to distinguish pathological features of incidentally-found growing meningiomas by comparing incidentally-found with symptomatic meningiomas. Methods. One hundred and thirty two consecutive nonrecurrent surgically-treated meningiomas treated between 2005 and 2007 were divided into three categories : 19 incidentally-found growing meningiomas (IG), 50 incidentallyfound meningiomas (I), and 63 symptomatic (S) meningiomas. The average follow-up period for the IG meningiomas was 3.7 years. Six out of 19 patients of the IG meningiomas became symptomatic during observation. Results. There is a significant difference of the incidence of WHO grades I, II, and III between all three groups (p=0.035). The incidence of WHO grades II and III in groups IG, I, and S were 26%, 2%, and 10%, respectively. We compare MIB-1 staining index between three groups : an average was 3.8% in IG, 1.3% in I, and 2.4% in S meningiomas. Conclusions. Incidentally-found meningiomas need careful follow-up. One fourth of the meningiomas that showed signs of growing belonged to the atypical or malignant grade.