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Condylar canal

The condylar canal, also known as the posterior condylar canal, is a small bony passage located in the posterior part of the occipital condyle near the foramen magnum. It transmits the emissary vein connecting the sigmoid sinus to the vertebral venous plexus, providing a route for venous drainage between the cranial cavity and the vertebral venous system. The canal is variable in size and may be unilateral, bilateral, or absent in some individuals. It lies posterolateral to the occipital condyle and is closely related to other cranial foramina at the skull base, making its recognition important in imaging of the posterior cranial fossa and occipital bone.

Synonyms

  • Posterior condylar canal

  • Foramen of the condylar vein

  • Condylar emissary foramen

Function

  • Provides a venous communication between the sigmoid sinus and vertebral venous plexus

  • Acts as a route for emissary veins to equalize intracranial and extracranial venous pressures

  • Plays a minor role in thermoregulation of intracranial venous blood

  • Can serve as a potential pathway for infection or tumor spread between intracranial and extracranial spaces

MRI Appearance
T1-weighted images:

  • The condylar canal appears as a small tubular structure of low signal intensity within the occipital condyle

  • Emissary veins within the canal may appear as flow voids if patent

  • Surrounding bone is intermediate signal, while adjacent soft tissue and fat provide subtle contrast

T2-weighted images:

  • Patent emissary veins appear hyperintense, contrasting with hypointense cortical bone

  • Surrounding soft tissues and cerebrospinal fluid in adjacent spaces help delineate the canal

STIR (Short Tau Inversion Recovery):

  • Suppresses fat signal from adjacent occipital and paraspinal tissues

  • Normal canal remains low signal; venous or soft tissue abnormalities appear hyperintense

CT Appearance

  • The condylar canal appears as a well-corticated, small bony channel within the occipital condyle

  • Easily visualized on axial, coronal, and sagittal planes, especially in bone window settings

  • Patency of the canal can be inferred from a small hypodense tubular lumen

  • Surrounding air of the nasopharyngeal or vertebral region provides natural contrast

MRI images

Condylar canal mri axial image -img-00000-00000