Quantitative morphological magnetic resonance imaging follow-up of low-grade glioma: a plea for systematic measurement of growth rates.

Supratentorial hemispheric diffuse low-grade gliomas (LGGs), i.e., World Health Organization grade II gliomas, are a heterogeneous group of tumors. During their natural course, LGGs tend to progress to a higher grade of malignancy, leading to neurological disability and ultimately to death. In this review, we will show, that during their low-grade period, these tumors exhibit systematically a spontaneous and continuous radiological growth, whatever their histological subtypes. The radiological tumor growth is easily quantified by measuring the evolution of the equivalent tumor diameter (calculated from the tumor volume), obtaining the velocity of diametric expansion (VDE). The spontaneous VDE of LGGs varies markedly with an average VDE of about 4 mm/year. It depends on intrinsic factors (1p19q codeletion status, P53 overexpression status) and can be modified by extrinsic factors (pregnancy). The spontaneous VDE carries a strong prognostic significance regarding progression-free and overall survivals. As a consequence, VDE should be integrated along with the other "static" parameters (multimodal imaging, histological and molecular analyses) in the initial investigations. In addition, the assessment of VDE obtained before, during, and after a particular oncological treatment helps in analyzing their effects on LGGs on an individual basis, helping to guide the decision making.