The Grade 1.5 Meningioma: Clinical Characteristics of an Aggressive Subset of Typically Benign Who Grade I Tumors

Objective: The World Health Organization has assigned three pathological grades to meningiomas that predict recurrence rates. Typically, Grade I meningiomas have the lowest recurrence rate and most benign clinical course. However, many clinicians have observed a small subset of Grade I lesions that behave more akin to their Grade II and III counterparts. We seek to define this subset of “aggressive” grade I tumors and describe their clinical characteristics.

Methods: We retrospectively reviewed the 832 patients with histologically confirmed meningioma at our institution from 2000–2012, with grades standardized to WHO 2007 criteria. 713 patients with Grade I meningioma assed for “aggressive” behavior, defined as a tumor that required repeat operation for recurrence within two years of gross total resection or a tumor with recurrence within two years that underwent radiosurgery and grew despite through treatment. Univariate and multivariate logistic regression were performed on potential risk factors for aggressive behavior, and 5-year progression free and overall survival distributions were plotted with Kaplan-Meier analysis.

Results: 24 tumors (3.7%) were aggressive by our criteria. 10.7% of all tumors recurred during the mean follow-up period of 49.1 (+/− 14.2) months. Aggressive tumors recurred at an average of 19.3 (+/− 12.1) months compared with 59.2 (+/− 17.3) months for benign tumors. Sex (p = .436), lesion size (p = .239), skull base on non-skull base location (p = .114), history of radiation exposure (p = .426), or embolization prior to surgery (p = .134) did not predict recurrence or aggressive behavior by Fisher exact test. By logistic regression younger age was predicted a 31.5% increased likelihood of aggression for every 10 years of age (odds ratio =.963). Kaplan-Meier distributions demonstrated 5-year progression free survival similar to Grade III tumors and overall survival similar to Grade I tumors.

Conclusion: We define a Grade 1.5 meningioma as an aggressively behaving Grade I meningioma with time to recurrence similar to Grade III lesions. Other than younger age, no clinical factors predicted aggressive clinical behavior. Further molecular based laboratory studies are needed to develop biomarkers for aggressive Grade I meningiomas.