Clinicopathological characteristics and prognostic factors of atypical meningiomas with bone invasion: a retrospective analysis of nine cases and literature review

Meningiomas are the most common primary neoplasms of the central nervous system in adults, arising from the arachnoid cap cells. Thus, grade 2 meningiomas are situated on the border between benignity and malignancy. Among the many prognostic factors that have been investigated in these tumors, bone invasion is one of them. The aim of our study was to identify whether bone invasion influences tumor recurrence and progression-free survival (PFS) in patients with atypical meningiomas (AMs). Out of 81 patients with AMs followed over a period of five years, we identified nine patients with bone invasion. We analyzed their demographic, clinical, imaging, and pathological characteristics, such as age, gender, radiological aspects, morphological features, extent of resection, recurrence rate, and PFS over a follow-up period of 60 months. Bone invasion was determined based on preoperative, surgical, and pathological reports. Out of the nine patients with bone invasion, four had convexity meningiomas, four had parasagittal meningiomas and one had a falcine meningioma. Regarding tumor recurrence∕progression, most patients (n=6) recurred within the first 24 months after surgery. Our study showed that the early recurrence/progression of tumor (at 12 months) correlated with extensive presence of malignancy criteria, especially with the presence of 15-18 mitoses∕10 high-power fields, as well as with large foci of spontaneous necrosis, but also with tumor bone infiltration, extensive bone lamellae destruction, and tumor infiltration of adjacent muscle with its atrophy due to tumor compression. Patients with bone invasion had a PFS of 29.3 months, compared to patients without invasion who had a higher PFS (49.3 months). Significant statistical associations were observed between bone invasion and tumor recurrence (p=0.002) and PFS (p=0.004). Our study emphasizes the importance of a thorough histopathological examination of the surgical specimen, which can provide significant data for the assessment of the progression of an AM [World Health Organization (WHO) grade 2] with bone invasion. AM infiltration in adjacent bone and muscle increases the rate of tumor recurrence and decreases PFS over a follow-up period of 60 months.