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Third ventricle

The third ventricle is a narrow, vertically oriented, slit-like midline cavity located in the diencephalon of the brain. It forms part of the ventricular system and is bounded laterally by the thalamus and hypothalamus. The third ventricle is connected anteriorly to the lateral ventricles via the foramen of Monro and posteriorly to the fourth ventricle through the cerebral aqueduct (aqueduct of Sylvius). It is filled with cerebrospinal fluid (CSF) and plays an essential role in the circulation of CSF within the central nervous system.

Synonyms:

  • Ventriculus tertius

  • 3rd ventricle

  • Third cerebral ventricle

  • Tertiary ventricle

MRI Appearance:

  • T1-weighted Images (T1):

    • The third ventricle appears as a low-signal (dark) CSF-filled space.

    • The surrounding brain parenchyma appears relatively hyperintense (brighter) compared to CSF.

    • The margins are sharply defined when CSF flow is normal and there is no obstruction.

  • T2-weighted Images (T2):

    • The third ventricle appears as a high-signal (bright) fluid-filled cavity due to the long T2 relaxation time of CSF.

    • The surrounding brain structures (thalamus, hypothalamus) show intermediate to low signal.

    • Its shape and size are best appreciated on coronal and axial sections.

  • FLAIR (Fluid Attenuated Inversion Recovery):

    • The third ventricle is seen as a low-signal (dark) region, as the CSF signal is suppressed.

    • Abnormal signal intensity within the ventricle may indicate pathology (e.g., pus, blood, high-protein fluid).

CT Appearance:

  • Non-contrast CT:

    • The third ventricle appears as a well-defined, hypodense (dark) midline structure due to the low attenuation of CSF.

    • The margins are easily visible if the ventricle is of normal size and not compressed or distorted.

    • The third ventricle may become more prominent with atrophy, hydrocephalus, or if pathology causes ventricular enlargement.

MRI images

Third ventricle mri 3t axial image

MRI images

Third ventricle mri 3t coronal image

MRI images

Third ventricle mri 3t sagittal image