Local Control Among Gross and Subtotally Resected Atypical Meningiomas Followed With Adjuvant Radiation or Observation

Abstract

Atypical meningiomas carry increased local recurrence (LR) rates and may benefit from adjuvant radiotherapy (RT) following both gross and subtotal resection. We hypothesize that subtotally resected (STR) atypical meningiomas treated with adjuvant RT and gross totally resected (GTR) atypical meningiomas followed by observation do not have different LR rates. We hypothesize that STR atypical meningiomas followed with observation experience unacceptably high local progression, which is significantly increased compared to those treated with adjuvant RT. All atypical meningiomas definitively resected with meeting 2016 World Health Organization (WHO) II criteria were included in this single institution retrospective analysis. Patients with prior brain RT or less than one year of radiographic follow up with MRI were excluded. GTR was defined as absence of clear enhancing tumor on post-operative MRI concordant with surgeon’s findings as dictated in the operative note, and STR was defined as residual enhancing tumor as noted on post-operative MRI or operative note. Adjuvant RT included both traditionally fractionated and stereotactic focal RT and defined as any RT delivered post operatively before progression noted on serial MRI. The primary end points of LR and PFS were estimated using the Kaplan Meier method. Cox proportional hazards model was used to evaluate differences in local control rates according to extent of resection and adjuvant RT. A tumor registry query of 2386 patients was reviewed, and 155 patients met inclusion criteria with median radiographic follow-up of 53.1 months (12-208 months). 115 (74.2%) patients were GTR while 40 (25.8%) were STR. Of the STR patients 24 (60%) were observed and 16 (40%) received adjuvant RT. Of those who received adjuvant RT, 16 were traditionally fractionated with median dose of 57.6 Gy (50.4, 60) and 4 received stereotactic focal RT with median dose of 13 (12, 27.5). The Kaplan-Meier estimate of LR at 5 years was 28.9% for patients with a GTR, 57.6% for patients with STR, and 34% for patients with STR followed by adjuvant RT. There was not a significant difference in LR rates between GTR patients followed by observation and STR patients treated with adjuvant RT (p= .667). STR patients followed with observation had significantly increased LR rate compared to those treated with adjuvant RT (p= .018). Observation of STR atypical meningiomas results in unacceptably high LR rates while STR followed by adjuvant RT significantly decreases the LR rate. The LR rate of STR patients who received adjuvant RT was not significantly different than GTR patients followed with observation.