Anatomical phenotyping and staging of brain tumors

In contrast to most other tumors, the anatomical extent of brain tumors is not objectified and quantified through staging. Staging systems are built on the understanding of the anatomical sequence of tumor progression and its relation to histopathological dedifferentiation and survival. While major advances in the understanding of primary brain tumors at a histological, cellular and molecular level have been achieved in recent decades, our understanding at a macroscopic anatomical level is limited. The aim of this study was to describe the anatomical phenotype of the most frequent brain tumor entities based on topographic probability and growth behavior analysis. The association of anatomical tumor features with survival probability was assessed and a prototypical staging system for WHO grade II-IV glioma was proposed based on the hypothesized anatomical sequence of tumor progression. The analysis is based on data from a consecutive cohort of 1000 patients with first diagnosis of a primary or secondary brain tumor. On preoperative MRI, the relative tumor density (RTD) of different topographic, phylogenetic and ontogenetic parcellation units was derived through normalization of the relative tumor prevalence to the relative volume of the respective structure. While primary central nervous system lymphoma (PCNSL) showed a high RTD along white matter tracts, the RTD in metastases was highest along terminal arterial flow areas. Neuroepithelial tumors (NT) demonstrated a high and homogeneous RTD along all sectors of the ventriculo-cortical axis, avoiding adjacent units, consistent with a transpallial behavior within phylo-ontogenetic radial units. Additionally, the topographic probability in NT correlated with morphogenetic processes of convergence and divergence of radial units during phylo- and ontogenesis. The anatomical tumor growth behavior was analyzed by comparing pre- and postoperative MRI, showing that a ventriculofugal growth dominates in NT. With progressive histopathological dedifferentiation of NT, a gradual deviation from this neuroepithelial anatomical behavior was found. By comparing survival probability, we identified prognostically critical steps in the anatomical behavior of NT. Based on a hypothesized sequence of anatomical tumor progression, we developed a three-level prototypical staging system for WHO grade II-IV glioma. This staging system proved to be accurate across histological, molecular, radiomorphological and clinical strata based on Kaplan Meier curves and multivariable survival analysis. Similar to staging systems for other tumors, a staging system such as this one may have the potential to inform stage-adapted treatment decisions.