Background: Diffusion weighted imaging (DWI) and apparent diffusion coefficient (ADC) map provide information on MRI about the cellularity of the tumor and have an important role in the pre-operative differentiation of different tumor types.
Objective: The aim of this work is to assess the role of diffusion MRI in differentiation between the most frequently encountered pediatric posterior fossa brain tumors.
Materials and methods: Twenty-four patients were prospectively included in this study. They were referred from the Neurosurgery Department. All of them were suspected to have posterior fossa SOL according to the contrast enhanced CT. All patients were subjected to conventional MRI followed by diffusion MR imaging and calculation of the ADC values.
Results: Twenty-four children (15 females) were included in the study. Their ages ranged between one and fifteen years old with a mean age of six years. Low-and high-grade tumors could be differentiated by using both absolute ADC values and ratios. Low-grade tumors showed statistically significantly higher ADC values (1.69±0.15 vs. 0.80±0.23) and ratios for tumor versus normal cerebellum (2.17±0.30 vs. 1.14±0.33) and tumor versus brain stem (1.88±0.35 vs. 1.06±0.24).The probability of error at 0.05 was considered significant, while at 0.01 and 0.001 was considered highly significant. Absolute ADC values and cerebellar and brainstem ratios were significantly higher in low-grade astrocytomas than in MBs. Overlap was found between ADC values of ATRTs and MBs.The sensitivity and specificity of a cutoff ADC value of > 1.083 x 10^-3mm²/s for differentiation of pilocytic astrocytomas from MBs and ependymomas were 100%.The sensitivity and specificity of a cutoff ADC value of ≤ 0.847 x 10^-3mm²/s for differentiation of medulloblastomas from PAs and ependymomas were 100%.The sensitivity and specificity of a cutoff ADC value of ≤ 1.083 x 10^-3mm²/s and > 0.847 x 10^-3mm²/s   for ependymomas were 100%.
Conclusion: The calculation of ADC value in the solid enhancing portion of a tumor is a simple and reliable technique for preoperative differentiation of the most common posterior fossa tumors.