To illustrate the most common magnetic resonance imaging (MRI) and computed tomography (CT) findings of posterior fossa tumors in pediatric age, to discuss the differential diagnosis and to make a checklist including key points for differential diagnosis of the most common pediatric brain tumors of posterior fossa: pilocytic astrocytoma, medulloblastoma, ependymoma and brainstem glioma.

Brain tumors are the most frequent solid neoplasm in children and the first cause of mortality in infancy. Having a pathological spectrum completely different to the adult one, the treatment of pediatric brain tumors presents many difficulties because of the nature of the developing brain. The localisation of the tumors according to patient age is as follow: 0 to 3 years old (yo) : supratentorial > infratentorial 4 to 10 yo : infratentorial > supratentorial 10 to early adult hood : infratentorial = supratentorial adults...

The standard MRI protocol for pediatric intracranialtumors includes volumetric fluid-attenuatedinversion recovery (FLAIR), sagittal and axial T1-, axialT2-, axial diffusion-, and postcontrast axial and coronal T1-weighted sequences. In suspected infratentorial tumors,postcontrast sagittal T1-weighted images are also obtained. A 1.5 tesla MRI was used to perform the exams. The protocol included a axial T1 and T2 spin echo acquisition completed according to the results by sagittal gradient echo, sagittal and axial T1 post gadolinium injection acquisition.

Conventional MRI is the primary imaging modality used for the evaluation of posterior fossa tumors in pediatric age. Advance MRI (DWI) discriminates much better between different types of pediatric brain tumors.Several studies (Yamasaki et al; Rumbolt et al; Schneider et al; Bull et al) demonstrated that pilocytic astrocytomas (PAs) are characterized by significantly higher average ADC values than ependymomas (EPs) and medulloblastomas, but no clear difference was shown between EPs and MBs. There is a considerable interest in developing new imaging tools to noninvasively predict...

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