Role of Magnetic Resonance Imaging (MRI) in the Diagnosis of Pediatric Posterior Fossa Tumors

Abstract
Aim and Objectives: To assess role of MRI in evaluation of space occupying lesions seen at the posterior fossa in pediatric age group.
Methodology: This study included 20 patients in pediatric age group suspected to have posterior fossa tumors with neurological symptoms and CT findings, all pateints underwent MRI brain with contrast with diffusion weighted images and ADC values were obtained.
Results: A total of 20 patients underwent MRI were: 12 males (60%) and 8 females (40%) their ages ranged from 8 months, according to conventional MRI findings the most common pediatric posterior fossa tumor was medulloblastoma in 8 cases followed by Ependymoma in 4 cases and JPA in 4 cases while pontine glioma was found in 3 cases and one case of schwannoma, based on DWI and ADC map cut off values of 0.9X10–3mm2/s were specific for medulloblastoma while cut off values more than 1.4 X 10–3mm2/s were specific for JPA. In cases of glioma and Schwannoma showed free diffusion with ADC values higher than 1 X 1 0–3mm2/s, cases of Ependymoma showed heterogeneous signal on DWI and ADC map with ADC value ranging from 1.01 and 1.3 X 10–3mm2/s suggesting restricted diffusion more than that seen in JPA cases. By comparing MRI findings with histopathology it was found that conventional MRI combined with DWI and ADC values show sensitivity 94% which is statistically significant positive strong correlation between MRI diagnosis and His-topathological confirmation.
Conclusion: Conventional MRI is the primary imaging modality used for the evaluation of posterior fossa tumors in pediatric age. Advance MRI (diffusion weighted images and ADC map) discriminates much better between different types of pediatric brain tumors. The study demonstrated that pilocytic astrocytomas (JPAs) are characterized by significantly higher ADC values than Ependymomas (EPs) and medulloblastomas, while medulloblastoma has the lowest ADC value, which seem to reliably provide the diagnosis which may affect the treatment plan and prognosis.