الفهرس 
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Abstract
Congenital posterior fossa malformations are a common group of disorders among the pediatric age group that represent wide range of cases which are in need for proper categorization to provide accurate prognostic and recurrence risk information, as well as guide further genetic evaluation and medical management.
The aim of the current study was to establish a pattern recognition approach of posterior fossa malformations & to delineate the role of MRI in diagnosis & meticulous characterization of these malformations.
The study was conducted on 75 children ranging from 1 month up to 10 years admitted to the pediatric Neurology Unit at Alexandria University Children’s Hospital (AUCH) in the time period between April 2017 and October 2019 with neurological dysfunction and clinical picture suggestive of underlying brain malformations.
MRI studies were done including conventional MRI (3D T1, T2, FLAIR, DWI and SWI) for all patients, while DTI was done in some selected cases.
Posterior fossa malformations were categorized into four categories according to the predominance of anatomical affection. These categories were a) Isolated cerebellar malformations including 15 patients (20%), b) Isolated brain stem malformations including 9 patients (12%), c) Combined cerebellar & brain stem malformations including 22 patients (29.3%) & d) posterior fossa malformations with supratentorial anomalies including 29 patients (38.6%).
Each category was studied thoroughly to detect special MRI features of each disease. The first pattern with predominant cerebellar affection included 6 main diseases, three of which were among the cystic posterior fossa malformations; classical Dandy Walker (five patients representing the largest group among this pattern), isolated inferior vermian hypoplasia (four patients) and persistent Blake’s pouch cyst (only one patient). The other three included disorders were macrocerebellum (2 patients), cerebellar dysplasia (2 patients) and rhombencephalosynapsis (only one patient).
The second pattern with malformations that affected only the brain stem included three main disorders; pontine tegmental cap dysplasia (PTCD) (four patients; representing the most common pattern), horizontal gaze palsy with progressive scoliosis (HGPPS) (three patients), and diencephalic-mesencephalic junction dysplasia(DMJD) (two patients).