Carotid canal

The carotid canal is a short but critical passage located in the petrous part of the temporal bone. It serves as a conduit for the internal carotid artery as it ascends into the cranial cavity to supply blood to the brain. This canal plays a vital role in neurovascular anatomy and is closely associated with several important structures of the skull base.

Structure

The carotid canal begins on the inferior surface of the temporal bone, specifically in the petrous part. It travels superiorly and medially in a slightly curved course and ends at the foramen lacerum at the base of the skull. The canal is generally about 4–5 mm in diameter and approximately 1–2 cm in length.

• External opening: Located on the inferior surface of the petrous temporal bone.
• Internal opening: Opens near the foramen lacerum but does not transmit structures into the foramen itself.
• Walls: Formed by dense bone of the petrous temporal region, offering protection to the internal carotid artery.

Location

The carotid canal is found within the petrous part of the temporal bone, at the base of the skull. Its external (inferior) opening is visible on the underside of the skull between the jugular foramen and the foramen magnum. Internally, it leads towards the middle cranial fossa, ending near the foramen lacerum.

Contents

The carotid canal primarily transmits the following structures:

• Internal carotid artery
• Internal carotid sympathetic plexus (nerve fibers from the superior cervical ganglion)
• Venous plexus accompanying the artery

Function

The carotid canal serves as a protective and guiding passage for the internal carotid artery as it enters the cranial cavity to supply the brain. The sympathetic plexus traveling with the artery provides autonomic innervation to intracranial structures.

Relations

• Anterior: Sphenoid bone and foramen lacerum
• Posterior: Jugular foramen and the sigmoid sinus
• Medial: Petrous apex and structures of the inner ear
• Lateral: Tympanic cavity and mastoid air cells

Clinical Significance

Knowledge of the carotid canal's anatomy is crucial in skull base surgeries and radiologic assessments. Pathologies involving the internal carotid artery, such as dissections or aneurysms, may have implications near this canal. Additionally, bone erosion due to tumors or infections can expose the artery, increasing the risk of hemorrhage.

Temporal bone fractures may affect the carotid canal, especially in high-velocity trauma, leading to arterial injury or arteriovenous fistula formation. Infections from the middle ear or mastoid may rarely spread towards the canal due to its proximity.

Imaging

On CT imaging, the carotid canal appears as a well-defined bony tunnel in the petrous temporal bone. MRI may demonstrate the flow void of the artery and enhancement of surrounding soft tissue in inflammatory or neoplastic conditions.

Development

The internal carotid artery forms early in embryogenesis, and the surrounding temporal bone ossifies to enclose the artery, creating the canal. The canal itself is not present at birth in complete form and finishes development during early childhood.