abnormal brain ventricle morphology abnormal fourth ventricle morphology MP:0000828 MPheno.ontology abnormal 4th ventricle morphology abnormal IVth ventricle morphology abnormal rhombencephalic ventricle morphology abnormal ventricle of rhombencephalon morphology abnormal ventriculus quartus morphology any structural anomaly of the irregularly shaped cavity in the rhombencephalon, between the medulla oblongata, the pons, and the isthmus in front, and the cerebellum behind; it is continuous with the central canal of the cord below and with the cerebral aqueduct above, and through its lateral and median apertures it communicates with the subarachnoid space fourth ventricle dysplasia abnormal hindbrain morphology