Glioblastoma multiforme regional genetic and cellular expression patterns: influence on anatomic and physiologic MR imaging

Abstract

Purpose: To determine whether magnetic resonance (MR) imaging is influenced by genetic and cellular features of glioblastoma multiforme (GBM) aggressiveness.

Materials and methods: In this HIPAA-compliant institutional review board-approved study, multiple enhancing and peritumoral nonenhancing stereotactic neurosurgical biopsy samples from treatment-naïve GBMs were collected prospectively, with guidance from cerebral blood volume (CBV) MR imaging measurements. By using monoclonal antibodies, tissue specimens were examined for microvascular expression, hypoxia, tumor and overall cellular density, and histopathologic features of GBM aggressiveness. Genetic expression patterns were investigated with RNA microarrays. Imaging and histopathologic variables were compared with the Welch t test and Pearson correlations. Microarray analysis was performed by using false discovery rate (FDR) statistics.

Results: Tumor biopsy of 13 adult patients yielded 16 enhancing and 14 peritumoral nonenhancing specimens. Enhancing regions had elevated relative CBV and reduced relative apparent diffusion coefficient (ADC) measurements compared with peritumoral nonenhancing biopsy regions (P < .01). A positive correlation was found between relative CBV and all histopathologic features of aggressiveness (P < .04). An inverse correlation was found between relative ADC and all histopathologic features of aggressiveness (P < .05). RNA expression patterns between tumor regions were found to be significantly different (FDR < 0.05), with hierarchical clustering by biopsy region only.

Conclusion: These findings suggest MR imaging is significantly influenced by GBM genetic and cellular biologic features of aggressiveness and imply physiologic MR imaging may be useful in pinpointing regions of highest malignancy within heterogeneous tissues, thus facilitating histologic grading of primary glial brain tumors.

Figure 1:

Histopathologic correlation of MR imaging with stereotactic biopsy specimens in patient 10, a 51-year-old man with a left temporal GBM. A, Axial three-dimensional spoiled gradient-recalled acquisition in the steady state T1-weighted contrast-enhanced image with, D, an aligned CBV map, and, G, an ADC map show preoperatively selected nonenhancing (pink circle) and enhancing (green circle) biopsy regions. B, C, Tissue specimens (corresponding to A) were stained with factor VIII monoclonal antibody and show normal delicate microvasculature (brown-stained cells) and complex hyperplastic microvasculature within, B, nonenhancing and, C, enhancing biopsy samples. (Factor VIII monoclonal antibody stain; original magnification ×20.) E, F, T2* signal intensity time curves (corresponding to D) from, E, nonenhancing and, F, enhancing regions show increased relative CBV (rCBV) and relative peak height (rPH) with reduced relative percentage of signal intensity recovery (rPSR) within the enhancing region. Peak height (PH) was calculated with the following equation: PH = S₀−S_min. Percentage of signal intensity recovery (PSR) was calculated with the following equation: PSR = (S₁−S_min)/(S_o−S_min), where S0 is the baseline precontrast signal intensity, Smin is the lowest signal intensity during the first passage of the intravascular contrast bolus, and S1 is the signal baseline during the recirculation steady-state phase after administration of the intravascular contrast material bolus. H, I, Histopathologic slides (corresponding to G) of, H, nonenhancing and, I, enhancing tissue samples stained for cellular mitosis show both biopsy samples infiltrated with malignant cells associated with increased mitotic activity (brown-stained cells) and overall cellularity within, I, enhancing regions correlating to areas of reduced ADC. (Mindbomb homolog 1 monoclonal antibody stain; original magnification ×20.)

Figure 2:

Presence of contrast enhancement is predictive of GBM genetic expression pattern. Right: Axial three-dimensional spoiled gradient-recalled acquisition in the steady state T1-weighted contrast-enhanced MR image obtained in the same patient as in Figure 1. Purple and green circles indicate nonenhancing and enhancing biopsy regions, respectively. Left: Genetic expression map of all biopsy samples with hierarchical clustering of the 500 most variant genes shows clustering only by biopsy sample. Purpleindicates nonenhancing samples; blue, gliosis samples; and green, enhancing samples. In the left column, biopsy location and sample number are provided for cross reference purposes with Table E1 [online]. Gliosis samples 1 through 6 were included as control samples to enable us to differentiate between gene expression due to astrocyte repair and scarring. These are not included in Table E1 [online]. RNA extracted from biopsy samples 1 and 5 was of insufficient quality to be hybridized to the microarray platform; therefore, these samples were not included in this analysis. Separate distinct sample locations from biopsies 24 and 25 were used twice in this genetic analysis. Bx = biopsy sample, G = gliosis sample.