Pineoblastoma with subarachnoid metastasis

8-month-old child presenting with irritability and increasing head circumference. Sagittal pre- (A) and postcontrast (B) T1-weighted MR images show a large, heterogeneous, minimally-enhancing pineal region mass (circle) that displaces both the brainstem and cerebellum. T2-weighted images (C, D, E) show hydrocephalus with ventriculomegaly of the lateral and third ventricles and transependymal edema. Hypointensity (arrows) on T2- (E) and T2*-weighted gradient echo images (F) is attributed to hemorrhage. Postcontrast T1-weighted image in the coronal plane (G) shows both hydrocephalus and an enhancing metastasis (arrowhead) in the left Sylvian fissure.