Grading Gliomas - Role of Diffusion Weighted Magnetic Resonance Imaging and Apparent Diffusion Coefficient (ADC) Values in Grading Gliomas

BACKGROUND \nThe central nervous system is a common site of tumorigenesis, where gliomas \nconstitute ~80% of primary malignant brain neoplasms. CNS neoplasms are first \nclassified into specific tumour types and then further graded as a measure of \nmalignancy. We wanted to evaluate the diffusion characteristics in high - and low \n- grade gliomas and correlate the ADC values of brain gliomas with the WHO \nhistopathological grades. \nMETHODS \nThe study group included 35 patients during the period of June 2017 to July 2018, \nwho had histopathologically proven gliomas of varying grades. The MRI images of \nthe patients (performed using a Siemens Magnetom Avanto 1.5T MRI machine at \nVictoria Hospital, Bangalore Medical College and Research Institute, Bangalore) \nwere reviewed retrospectively. MRI detected cases of Gliomas without HPE reports \nand patients with postoperative recurrent tumours, were excluded from the study \ngroup. \nRESULTS \nThe most common age group was found to be 40 to 59 years, with a distinct male \npredilection. MR images revealed diffusion restriction in cases of glioma, differing \nonly in the amount of restriction as assessed by the corresponding mean and \nminimum ADC values. It was noted that the mean and minimum ADC values were \nrelatively higher for cases of low grade gliomas, when compared to that obtained \nfrom high grade gliomas. The average minimum ADC values were 1.11 (grade I \ntumour), 0.96 (grade II tumour), 0.92 (grade III tumour) and 0.74 (grade IV \ntumour). The average mean ADC values were 1.19 (grade I tumour), 1.05 (grade \nII tumour), 0.98 (grade III tumour) and 0.86 (grade IV tumour). Statistical \nsignificance was found between the calculated ADC values and the \nhistopathological tumour grade (p value was <0.001 for both values). \nCONCLUSIONS \nOur study confirmed that diffusion weighted MR imaging with ADC (both mean \nand minimum) value measurements, can be used to differentiate high - and low - \ngrade gliomas in a non-invasive method for approximating tumour grade. We \ndemonstrated that as the tumour cellularity and the grade increases, both the \nmean and minimum ADC values decrease.