Carotid canal !

The carotid canal is a bent tunnel through the temporal bone that carries the internal carotid artery, a main blood supply of the brain, into the skull.

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What it is

A bent canal through the petrous temporal bone.

What it does

Carries the internal carotid artery into the skull.

Key facts

Where: Petrous part of the temporal bone
Function: Transmits the internal carotid artery and its sympathetic plexus

Relations

Contents: Petrous segment of the internal carotid artery, wrapped in its sympathetic (internal carotid) plexus and a small venous plexus
Course: Outer opening on the inferior surface of the petrous part, just in front of the jugular foramen; a short vertical part, a bend (genu), then a horizontal part running forward and medially to the inner opening at the petrous apex
Lateral: The middle ear and the bony part of the auditory tube: the lower anterior wall of the tympanic cavity is only a thin plate over the vertical part; the cochlea lies close behind the bend
Above: The trigeminal ganglion rests over the horizontal part near the apex, where the bony roof can be thin or missing
Behind: Jugular foramen with the internal jugular vein and nerves IX, X and XI, separated from the outer opening by a ridge of bone

How to find it

It cannot be felt. On the underside of a dry skull its round outer opening lies just in front of the jugular foramen; from inside the middle cranial fossa its inner opening is seen at the petrous apex, next to the foramen lacerum.

On imaging

Thin-slice CT of the skull base with bone windows shows the canal and any fracture crossing it; CT angiography or MR angiography shows the petrous internal carotid artery when dissection or injury is suspected.

Clinical notes

Internal carotid artery dissection classically combines one-sided head or neck pain with a partial Horner syndrome (small pupil, slight ptosis, no loss of sweating on the face)
In middle fossa and petrous apex surgery the canal is a key landmark; a thin or open roof leaves the artery exposed under the trigeminal ganglion
A thin or deficient wall between the canal and the middle ear puts the artery at risk in ear surgery and can cause pulsatile tinnitus

Anatomical variants

Aberrant internal carotid artery: a rare course through the middle ear instead of the canal, seen as a red mass behind the eardrum that can be mistaken for a tumour
Dehiscence of the bony wall between the canal and the tympanic cavity or the sphenoid sinus, found on CT

Test yourself

Think of the answer, then tap the question to see it.

Which structures pass through the carotid canal?

The petrous segment of the internal carotid artery, wrapped in its sympathetic plexus and a small venous plexus.

Why does injury to the internal carotid artery in the carotid canal give Horner syndrome?

The sympathetic fibres from the superior cervical ganglion ride on the artery to the pupil dilator and the upper eyelid.

What is the classic presentation of an internal carotid artery dissection?

One-sided head or neck pain with a partial Horner syndrome: small pupil, slight ptosis and no loss of facial sweating.

Why does a skull base fracture crossing the carotid canal call for vascular imaging?

It raises concern for carotid injury: dissection, occlusion or a false aneurysm.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): canalis carotidis TA2 651
Official Spanish (DeCS): Conducto carotídeo
English (TA2): Carotid canal

Sources: Terminologia Anatomica (TA2); Anatomy, Head and Neck, Skull Foramen; Anatomy, Head and Neck: Internal Carotid Arteries.

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Representative model, for educational purposes only.