J Neurosurg 106:846–854, 2007 846 J. Neurosurg. / Volume 106 / May, 2007 TYPICAL and malignant meningiomas are character- ized by successive recurrences and aggressive be- havior even after complete resection. Their report- ed incidence among all meningiomas varies, ranging from 4.7 to 6.2% for atypical tumors and from 1.0 to 1.7% for malignant tumors. 10,22,31 Classification of meningiomas has been revised substantially over the last 20 years, with the aim of defining clear criteria for each meningioma variant. The most recent (2000) revision of the WHO meningioma classification system has been well accepted in the litera- ture and provides reasonably good prognostic correlation. 10, 25,47 Borderline cases exist in all grading schemes. Recur- rence and high proliferation rates have been reported in other- wise histologically benign meningiomas. 10,21 An increase in tumor grade (malignant progression) may be noted with suc- cessive recurrences of benign or atypical meningiomas. This aspect is not extensively discussed in the literature, but au- thors of some case series have reported incidence rates rang- ing from 1.6 to 2% of meningiomas. 22,31,41 Adjuvant EBRT has been shown to decrease the inci- dence of tumor recurrence in aggressive meningiomas and improve patient survival rates after subtotal resection. 18,34 Although the effectiveness of SRS and SRT is well recog- nized for benign meningiomas, 3,7,11,15,27,33,42,45,46 few authors have reported on case series in which patients with atypical Stereotactic radiation treatment for recurrent nonbenign meningiomas CARLOS A. MATTOZO, M.D., 1 ANTONIO A. F. DE SALLES, M.D., PH.D., 1 IVAN A. KLEMENT , M.D., 2 ALESSANDRA GORGULHO, M.D., 1 DAVID MCARTHUR,PH.D., 1 JUDITH M. FORD, M.D., PH.D., 3 NZHDE AGAZARYAN,PH.D., 3 DANIEL F. KELLY , M.D., 1 AND MICHAEL T. SELCH, M.D. 3 1 Division of Neurosurgery and Departments of 2 Pathology and 3 Radiation Oncology, University of California at Los Angeles School of Medicine, Los Angeles, California Object. The authors analyzed the results of stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) for the treatment of recurrent meningiomas that were described at initial resection as showing aggressive, atypical, or malignant features (nonbenign). Methods. Twenty-five patients who underwent SRS and/or SRT for nonbenign meningiomas between December 1992 and August 2004 were included. Thirteen of these patients underwent treatment for multiple primary or recurrent lesions. In all, 52 tumors were treated. All histological sections were reviewed and reclassified according to World Health Organization (WHO) 2000 guidelines as benign (Grade I), atypical (Grade II), or anaplastic (Grade III) menin- giomas. The median follow-up period was 42 months. Seventeen (68%) of the cases were reclassified as follows: WHO Grade I (five cases), Grade II (11 cases), and Grade III (one case). Malignant progression occurred in eight cases (32%) during the follow-up period; these cases were con- sidered as a separate group. The 3-year progression-free survival (PFS) rates for the Grades I, II, and III, and malignant progression groups were 100, 83, 0, and 11%, respectively (p  0.001). In the Grade II group, the 3-year PFS rates for patients treated with SRS and SRT were 100 and 33%, respectively (p = 0.1). After initial treatment, 22 new tumors re- quired treatment using SRS or SRT; 17 (77%) of them occurred inside the original resection cavity. Symptomatic ede- ma developed in one patient (4%). Conclusions. Stereotactic radiation treatment provided effective local control of “aggressive” Grade I and Grade II meningiomas, whereas Grade III lesions were associated with poor outcome. The outcome of cases in the malignant progression group was intermediate between that of the Grade II and Grade III groups, with the lesions showing a ten- dency toward malignancy. KEY WORDS • atypical meningioma • brain tumor • meningioma • malignant meningioma • radiosurgery • tumor classification A Abbreviations used in this paper: EBRT = external-beam radia- tion therapy; GKS = Gamma Knife surgery; MR = magnetic reso- nance; PFS = progression-free survival; SRS = stereotactic radio- surgery; SRT = stereotactic radiotherapy; WHO = World Health Organization.