Fig. 1

Three examples of causes of obstructive hydrocephalus in different patients due to different intracranial tumours. a Sagittal post-contrast T1-weighted MRI image showing a medulloblastoma in the fourth ventricle with mass effect on the brainstem (solid white arrow). There are no early signs of hydrocephalus—the floor of the third ventricle is not bulging inferiorly (dashed white arrow)—despite the compression of the brainstem. b Axial T2-weighted MRI image in patient with a pilocytic astrocytoma in the posterior fossa (black arrow) with signs of hydrocephalus and dilatation of the temporal horns (solid white arrow) of the lateral ventricles and inferior dilatation of the third ventricle (dashed white arrow)