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Fourth ventricle

The fourth ventricle is a diamond-shaped cavity within the brainstem, located between the brainstem (pons and medulla) anteriorly and the cerebellum posteriorly. It is part of the ventricular system, which contains cerebrospinal fluid (CSF) and communicates with the third ventricle via the cerebral aqueduct and with the central canal of the spinal cord. Its boundaries, connections, and characteristic imaging features make it an essential structure for radiologists and neurologists to identify in both clinical and academic settings.

Synonyms

  • 4th ventricle

  • Ventriculus quartus

  • IV ventricle

Function

  • Circulation of cerebrospinal fluid (CSF) between the cerebral aqueduct and the central canal of the spinal cord.

  • Acts as a conduit for CSF flow to the subarachnoid space through the median aperture (foramen of Magendie) and lateral apertures (foramina of Luschka).

  • Helps protect the brain from trauma by cushioning it with CSF.

MRI Appearance

  • T2-Weighted MRI:

    • The fourth ventricle appears as a well-defined, hyperintense (bright) CSF-filled space posterior to the pons and anterior to the cerebellum.

    • The surrounding brain tissue appears darker (hypointense) compared to CSF.

    • Clear delineation from the adjacent structures.

  • T1-Weighted MRI:

    • The CSF within the fourth ventricle appears hypointense (dark/black).

    • The ventricle’s margins are sharply outlined by the slightly higher signal of the brainstem and cerebellar tissue.

  • FLAIR MRI:

    • The CSF signal in the fourth ventricle is suppressed (very dark/hypointense).

    • Any abnormal signal within the ventricle (such as pus, blood, or tumor) would appear hyperintense (bright), aiding in the detection of pathology.

CT Appearance

  • On non-contrast CT, the fourth ventricle appears as a well-demarcated, hypodense (dark) CSF-filled space.

  • Located in the midline, posterior to the brainstem and anterior to the cerebellum.

  • Normally, no enhancement is seen unless there is adjacent pathology (e.g., tumors, hemorrhage, or infection).

  • In cases of hydrocephalus, the fourth ventricle may be dilated.

MRI images

Fourth ventricle mri coronal 3t image

MRI image

Fourth ventricle

CT image

CT Fourth ventricle sag anatomy image -img-00000-00000