Axial CT without contrast of the brain (above) shows moderate dilation of the lateral, third and fourth ventricles. Axial T2 MRI without contrast of the brain (below left) shows a round focus of bright signal in the posterior medulla that on the sagittal T1 MRI post contrast (below right) shows it to be a non-enhancing mass in the floor of the fourth ventricle causing ventricular outlet obstruction.
Pediatric Imaging 