DOI: 10.1007/s00259-018-4107-zPages: 1-11

Region-by-region analysis of PET, MRI, and histology in en bloc-resected oligodendrogliomas reveals intra-tumoral heterogeneity

1. Uppsala University, University Hospital, Department of Neuroscience, Neurology

2. Uppsala University, Department of Surgical Sciences, Radiology

3. Uppsala University, Department of Information Technology, Division of Visual Information and Interaction

4. Uppsala University, Department of Immunology, Genetics and Pathology, Rudbeck Laboratory

5. Uppsala University, Department of Neuroscience, Section of Neurosurgery

6. Uppsala University, Department of Immunology, Genetics and Pathology and Science for Life Laboratory

7. Uppsala University Hospital, Department of Radiology

8. University of Gothenburg, Institute of Neuroscience and Physiology, Department of Clinical Neuroscience, Sahlgrenska Academy

Correspondence to:
Kenney Roy Roodakker
Tel: +46 70 49 19 767
Email: kenney.roodakker@neuro.uu.se

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Abstract

Purpose

Oligodendrogliomas are heterogeneous tumors in terms of imaging appearance, and a deeper understanding of the histopathological tumor characteristics in correlation to imaging parameters is needed. We used PET-to-MRI-to-histology co-registration with the aim of studying intra-tumoral 11C-methionine (MET) uptake in relation to tumor perfusion and the protein expression of histological cell markers in corresponding areas.

Methods

Consecutive histological sections of four tumors covering the entire en bloc-removed tumor were immunostained with antibodies against IDH1-mutated protein (tumor cells), Ki67 (proliferating cells), and CD34 (blood vessels). Software was developed for anatomical landmarks-based co-registration of subsequent histological images, which were overlaid on corresponding MET PET scans and MRI perfusion maps. Regions of interest (ROIs) on PET were selected throughout the entire tumor volume, covering hot spot areas, areas adjacent to hot spots, and tumor borders with infiltrating zone. Tumor-to-normal tissue (T/N) ratios of MET uptake and mean relative cerebral blood volume (rCBV) were measured in the ROIs and protein expression of histological cell markers was quantified in corresponding regions. Statistical correlations were calculated between MET uptake, rCBV, and quantified protein expression.

Results

A total of 84 ROIs were selected in four oligodendrogliomas. A significant correlation (p < 0.05) between MET uptake and tumor cell density was demonstrated in all tumors separately. In two tumors, MET correlated with the density of proliferating cells and vessel cell density. There were no significant correlations between MET uptake and rCBV, and between rCBV and histological cell markers.

Conclusions

The MET uptake in hot spots, outside hotspots, and in infiltrating tumor edges unanimously reflects tumor cell density. The correlation between MET uptake and vessel density and density of proliferating cells is less stringent in infiltrating tumor edges and is probably more susceptible to artifacts caused by larger blood vessels surrounding the tumor. Although based on a limited number of samples, this study provides histological proof for MET as an indicator of tumor cell density and for the lack of statistically significant correlations between rCBV and histological cell markers in oligodendrogliomas.

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  • Accepted: Jul 20, 2018
  • Online: Aug 14, 2018

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