The fourth venticle is a cavitie which lies posterior to the pons and upper half of the medulla oblongata and anterior to the cerebellum. It is continuous with the cerebral aqueduct (mesencephalic or Sylvius) above and the central canal of the spinal cord in the lower half of the medulla. On each size, a narrow prolongation, the lateral recess, projects around the brainstem; its lateral aperture (forame of Luschka) lies below the cerebellar flocculus.

The fourth ventricle has lateral boundaries, a roof and a floor. The lateral boundaries are formed on each side by the superior cerebellar peduncle, the inferior cerebellar peduncle and the cuneate and gracile tubercles.

Roof of the fourth ventricle - Formed by thin laminae of white matter. The lower has a median aperture (foramen of Magendie); cerebrospinal fluid escapes through this opening and lateral apertures into the subarachnoid space. Because these are the only communications between the ventricular and subarachnoid spaces, their blockage can produce one type of hydrocephalus.

The floor of the fourth ventricle, also known as rhomboid fossa, is formed by the dorsal surfaces of the pons and medulla oblongata.

The cerebral aqueduct is a narrow canal in the midline connecting the third and fourth ventricle. It is 1.5 cm long and 1-2 mm, in diameter. Its floor is formed by the tegmentum of the midbrain. Its roof consists of the quadrigeminal body of the midbrain and posterior comissure.

The tela choroidea is a layer of pia mater of great vascularity which invaginates close to the median plane into the cavity of the fourth ventricle to form the choroid plexus of the fourth ventricle. Anotomic findings indicate that the average normal ventricular system has a capacity of less than 16 ml.

Author: Silvia Helena Cardoso, PhD. Psychobiologist, master and doctor in Sciences by the University of São Paulo and post doctoral fellowship by the University of California, Los Angeles. Invited Professor and Associate Researcher of the Center for Biomedical Inofrmatics, State University of Campinas (Unicamp), Brazil.

Reviewed and commented by the neuroanatomist Dr. Norberto Cysne Coimbra , MD, PhD. Neuoanatomist, Neuroscientist, Molecular Biologist. Laboratory of Neuroanatomy and Neuropsichobiology, Department of Morphology, Faculty of Medicine, Ribeirão-Preto USP (São Paulo), Brazil.

Translation: Silvia Helena Cardoso