Sagittal and axial CISS reconstructions through the fourth ventricle.
Key structures include:
floor of fourth ventricle (along the dorsal pontomedullary surface, also known as the rhomboid fossa)
cerebral aqueduct (sagittal) / aqueduct of Sylvius (axial)
roof of fourth ventricle (along the cerebellar vela)
the peak of the ventricle in the cerebellum is the fastigium
flow into cisterna magna via the median aperture (foramen of Magendie)
flow into the cerebellopontine angle via the lateral apertures (foramina of Luschka)
the most interior point is the obex, which passes into the central canal of the spinal cord