Molecular typing of Meningiomas by Desorption Electrospray Ionization Mass Spectrometry Imaging for Surgical Decision-Making

Abstract

Meningiomas are the most frequent intracranial tumors. The majority is benign slow-growing tumors but they can be difficult to treat depending on their location and size. While meningiomas are well delineated on magnetic resonance imaging by their uptake of contrast, surgical limitations still present themselves from not knowing the extent of invasion of the dura matter by meningioma cells. The development of tools to characterize tumor tissue in real or near real time could prevent recurrence after tumor resection by allowing for more precise surgery, i.e. removal of tumor with preservation of healthy tissue. The development of ambient ionization mass spectrometry for molecular characterization of tissue and its implementation in the surgical decision-making workflow carry the potential to fulfill this need. Here, we present the characterization of meningioma and dura mater by desorption electrospray ionization mass spectrometry to validate the technique for the molecular assessment of surgical margins and diagnosis of meningioma from surgical tissue in real-time. Nine stereotactically resected surgical samples and three autopsy samples were analyzed by standard histopathology and mass spectrometry imaging. All samples indicated a strong correlation between results from both techniques. We then highlight the value of desorption electrospray ionization mass spectrometry for the molecular subtyping/subgrouping of meningiomas from a series of forty genetically characterized specimens. The minimal sample preparation required for desorption electrospray ionization mass spectrometry offers a distinct advantage for applications relying on real-time information such as surgical decision-making. The technology here was tested to distinguish meningioma from dura mater as an approach to precisely define surgical margins. In addition we classify meningiomas into fibroblastic and meningothelial subtypes and more notably recognize meningiomas with NF2 genetic aberrations.

Keywords: CNS; DESI; DESI-MSI; H&E; MS; MSI; PCA; ROI; iMRI; meningioma; real-time diagnosis; subtyping; surgery.

Figure 1

Optical images of the samples H&E stained after MSI analysis of surgical samples A1 (a) and J10 (b), and post-mortem sample PM3 (c) tissue sections analyzed by DESI-MSI (left panels). Squares delineate regions corresponding to the magnified images presented in middle panels. Right panels display the DESI-MSI ion images of each sample representing the distribution of an ion at m/z value 682.7.

Figure 2

Average mass spectra of the phospholipid content of case 41 secretory meningioma WHO grade I (a). Insets show optical images of the sections stained with H&E after DESI-MSI analysis of A1 (tumor) and J10 (dura), respectively. Score plot of the two first principal components (in red the tumor group, n=81 and in green the dura group, n=69) (b). Loading plot of the first and second principal components (c). m/z values correspond to the ions preferentially detected in high cellularity regions (i.e. meningioma).

Figure 3

Label-free 3D molecular imaging of tumor presentation with DESI-MS. (a) 3D visualization of DESI-MSI results over MRI segmented tumor volume for surgical case 41. The MRI was acquired preoperatively, and the tumor segmented and modeled using Slicer 4.0. Inset shows the overall tumor volume in light green. The position of each stereotactic sample was digitally registered to the pre-operative MRI using BrainLab iplan cranial 3.0, and the corresponding 3 dimensional coordinates used to render the distribution of the DESI-MSI analyses in the 3D tumor volume. The warm color scale from yellow to red represents the relative intensity of the peak at m/z 682.7. (b) Results are further visualized on axial sections of post-contrast T1 MR images. (c) Intensity values of the peak at m/z 682.7 for each surgical sample and autopsy. Arrow shows the dural tail. S, superior, A, anterior, L, lateral, P, posterior.

Figure 4

Meningioma subtypes and subgroups. Each subgroup is characterized by the absence or the presence of the mutations listed in the figure.

Figure 5

Average mass spectra of the phospholipid content of fibroblastic (in red) and meningothelial (in green) wild type NF2 meningioma samples (a). Insets show optical images of the sections stained with H&E after DESI-MSI analysis of MG-13 (fibroblastic) and MG-6 (meningothelial) samples, respectively. Arrows of upper average mass spectrum display phospholipids presenting specific relative abundance between each sample. Score plot of the two first principal components (in red the fibroblastic group, n=165 and in green the meningothelial group, n=346) (b). Circle indicates mass spectra acquired during DESI-MSI analysis of sample MG-6.

Figure 6

Average mass spectra of the phospholipid content of fibroblastic meningioma samples wild type NF2 (red) or NF2 mutated (green) (a). Insets show optical images of the sections stained with H&E after DESI-MSI analysis of MG-13 (wild type NF2 fibroblastic meningioma) and MG-25 (NF2 mutated fibroblastic meningioma) samples, respectively. Score plot of the two first principal components (in red the wild type NF2 fibroblastic group, n=165 and in green the NF2 mutated fibroblastic group, n=748) (b).