Intraoperative Flow Cytometry for the Evaluation of Meningioma Grade

Abstract

Meningiomas are the most frequent central nervous system tumors in adults. The majority of these tumors are benign. Nevertheless, the intraoperative identification of meningioma grade is important for modifying surgical strategy in order to reduce postoperative complications. Here, we set out to investigate the role of intraoperative flow cytometry for the differentiation of low-grade (grade 1) from high-grade (grade 2-3) meningiomas. The study included 59 patients. Intraoperative flow cytometry analysis was performed using the 'Ioannina Protocol' which evaluates the G0/G1 phase, S-phase, mitosis and tumor index (S + mitosis phase fraction) of a tumor sample. The results are available within 5 min of sample receipt. There were 41 grade 1, 15 grade 2 and 3 grade 3 meningiomas. High-grade meningiomas had significantly higher S-phase fraction, mitosis fraction and tumor index compared to low-grade meningiomas. High-grade meningiomas had significantly lower G0/G1 phase fraction compared to low-grade meningiomas. Thirty-eight tumors were diploids and twenty-one were aneuploids. No significant difference was found between ploidy status and meningioma grade. ROC analysis indicated 11.4% of tumor index as the optimal cutoff value thresholding the discrimination between low- and high-grade meningiomas with 90.2% sensitivity and 72.2% specificity. In conclusion, intraoperative flow cytometry permits the detection of high-grade meningiomas within 5 min. Thus, surgeons may modify tumor removal strategy.

Keywords: grade of malignancy; intraoperative flow cytometry; meningioma.

Figure 1

Cell cycle distribution analysis using intraoperative flow cytometry in a grade 1 meningioma. Markers M1, M2 and M3 represent G₀/G₁, S and G₂/M cell cycle phases, respectively (absolute quantification of each marker is presented in the top right corner in each histogram). On the left of each figure the cell cycle distribution of peripheral blood mononuclear cells (PBMCs) is presented as a control. The presented case is diploid, with a DNA index = 1, while the tumor index (i.e., percentage of proliferative cells) was calculated at ~7%. In the overlay histogram, the G₀/G₁ peak of cancer cells in red is discernible from that of normal cells in green.

Figure 2

Cell cycle distribution analysis using intraoperative flow cytometry in a higher-grade meningioma. PBMCs and cancer cells are represented as in Figure 1, with respective markers M1, M2 and M3 representing G₀/G₁, S and G₂/M cell cycle phases (presented as quantified in the top right corner of each histogram). The case exhibits a DNA index = 1 and a tumor index = 29%. In the overlay histogram, the G0/G1 peak of cancer cells in red is discernible from that of normal cells in green.

Figure 3

Receiver operating characteristic curve analysis in differentiating grade 1 from grade 2/3 meningiomas, based on tumor index calculation. The area under the curve was 0.825.