Vessels of Head
Internal Carotid Artery (ICA) Overview
● Origin: Terminal branch of the common carotid artery in the carotid triangle of the
neck.
● Level: Upper border of thyroid cartilage ≈ disc between C3 and C4 vertebrae.
Vital Structures at the Carotid Bifurcation
● Carotid sinus:
○ Dilatation at the origin of internal carotid artery (ICA).
○ Baroreceptors in tunica media monitor blood pressure.
○ Afferent via glossopharyngeal nerve (CN IX).
○ Efferent via vagus nerve (CN X) (baroreceptor reflex).
● Carotid body:
○ Small mass of glomus tissue adjacent to sinus.
○ Chemoreceptors sensitive to O₂ partial pressure.
○ Afferent via CN IX, efferent via CN X (chemoreceptor reflex).
Parts of the ICA
Prior to entering the cranial cavity
1. Cervical part:
○ Begins at carotid bifurcation.
○ Ascends anterior to transverse processes of C1–C3 vertebrae.
○ Passes deep to posterior belly of digastric and styloid process.
○ Ends at inferior aperture of carotid canal.
○ Surrounded by sympathetic plexus from superior cervical ganglion.
○ No branches.
2. Petrous part:
○ Ascends through carotid canal in petrous temporal bone.
○ Curves forwards and medially (near trigeminal ganglion).
○ Enters foramen lacerum.
○ Branches:
■ Carotico-tympanic artery: Enters tympanic cavity via carotid canal
foramen.
■ Artery of the pterygoid canal: Runs with deep petrosal and greater
petrosal nerves.
,Within the cranial cavity
3. Cavernous part:
○ Lies within cavernous sinus, covered by endothelium.
○ Travels from foramen lacerum → dorsum sellae → anterior clinoid process.
○ Emerges from dural roof of sinus under brain.
○ Branches:
■ Trigeminal ganglion branch.
■ Inferior hypophyseal artery → posterior lobe of pituitary gland.
■ Meningeal branches → anterior/middle cranial fossa + tentorium
cerebelli.
4. Cerebral part:
○ Lies in subarachnoid space.
○ Turns backward below optic nerve, then ascends to terminal branches.
○ Segments:
■ C5: Ascends to dorsum sellae.
■ C4: Turns forward along sphenoid body.
■ C3: Curves up to anterior clinoid process.
■ C2: Turns backward below optic nerve.
■ C1: Ascends to divide into terminal branches.
○ C5, C4, C3 = cavernous part.
○ C2, C1 = cerebral part.
○ C4 → C2 = forward convex U-turn = carotid siphon.
Branches of ICA Prior to Termination (Cerebral Part)
● Ophthalmic artery
● Superior hypophyseal artery
● Posterior communicating artery
● Anterior choroidal artery
Ophthalmic Artery
● Main branch of ICA (supplies all orbital structures).
● Course:
○ Enters orbit via optic canal (inferolateral to optic nerve).
○ Arches over optic nerve, then forwards on medial orbital wall.
Branches of Ophthalmic Artery
1. Central retinal artery:
○ Pierces optic nerve → supplies retina (anatomical end artery).
○ Occlusion → blindness.
2. Ciliary arteries (long, short, anterior):
○ Supply sclera, choroid, intraocular muscles.
, 3. Muscular branches:
○ Supply extraocular muscles, give rise to anterior ciliary arteries.
4. Lacrimal artery:
○ Lateral to optic nerve → supplies lacrimal gland + lateral eyelids (via lateral
palpebral).
5. Supraorbital artery:
○ Exits orbit via supraorbital foramen, supplies scalp.
6. Posterior ethmoidal artery:
○ Exits via posterior ethmoidal foramen → ethmoidal air cells, nasal septum
(upper part).
7. Anterior ethmoidal artery:
○ Exits via anterior ethmoidal foramen → ethmoidal air cells, frontal sinus,
anterior nasal septum.
8. Medial palpebral arteries:
○ Supply medial eyelids.
9. Dorsal nasal artery:
○ To dorsum of nose.
10. Supratrochlear artery:
● Forehead.
Terminal Branches of the ICA
● Anterior cerebral artery
● Middle cerebral artery
Anterior Cerebral Artery (ACA)
● Right and left ACAs connected by anterior communicating artery (completes anterior
circle of Willis).
● Segments:
○ A1: Precommunicating part.
○ A2: From anterior communicating to callosomarginal artery origin.
○ A3: Continuation = pericallosal artery.
Middle Cerebral Artery (MCA)
● Segments:
○ M1: Horizontal part (on sphenoid).
○ M2: Insular part (lateral sulcus).
○ M3: Opercular part (emerges from lateral sulcus).
○ M4: Cortical part.
, Anastomoses Between ICA and ECA
● Main sites: Scalp, nasal cavity, orbit.
Scalp
● Supraorbital artery (ICA) ↔ Frontal branch of superficial temporal artery (ECA).
● Rich blood supply = profuse bleeding, but rapid healing.
Nasal Cavity
● Little's area / Kiesselbach’s plexus:
○ Anterior ethmoidal artery (ICA) ↔
■ Posterior septal branch of sphenopalatine artery (maxillary, ECA)
■ Septal branch of superior labial artery (facial, ECA).
○ Common site of epistaxis (nosebleeds).
● Posterior ethmoidal artery (ICA) ↔ Posterior septal branch of sphenopalatine
artery (ECA):
○ Less common, more difficult to control bleeding.
Medial Orbital Margin
● Dorsal nasal artery (ICA) ↔
○ Angular artery, lateral nasal artery (facial, ECA).
Superior Orbital Fissure
● Recurrent meningeal branch of lacrimal artery (ICA) ↔
○ Anterior branch of middle meningeal artery (maxillary, ECA).
Brain Circulation and Coverings- Arteries of the Brain
Arterial Supply of the Brain
Supplied by Four Arteries
● A pair of internal carotid arteries (ICA)
● A pair of vertebral arteries
Internal Carotid Artery (ICA) Overview
● Origin: Terminal branch of the common carotid artery in the carotid triangle of the
neck.
● Level: Upper border of thyroid cartilage ≈ disc between C3 and C4 vertebrae.
Vital Structures at the Carotid Bifurcation
● Carotid sinus:
○ Dilatation at the origin of internal carotid artery (ICA).
○ Baroreceptors in tunica media monitor blood pressure.
○ Afferent via glossopharyngeal nerve (CN IX).
○ Efferent via vagus nerve (CN X) (baroreceptor reflex).
● Carotid body:
○ Small mass of glomus tissue adjacent to sinus.
○ Chemoreceptors sensitive to O₂ partial pressure.
○ Afferent via CN IX, efferent via CN X (chemoreceptor reflex).
Parts of the ICA
Prior to entering the cranial cavity
1. Cervical part:
○ Begins at carotid bifurcation.
○ Ascends anterior to transverse processes of C1–C3 vertebrae.
○ Passes deep to posterior belly of digastric and styloid process.
○ Ends at inferior aperture of carotid canal.
○ Surrounded by sympathetic plexus from superior cervical ganglion.
○ No branches.
2. Petrous part:
○ Ascends through carotid canal in petrous temporal bone.
○ Curves forwards and medially (near trigeminal ganglion).
○ Enters foramen lacerum.
○ Branches:
■ Carotico-tympanic artery: Enters tympanic cavity via carotid canal
foramen.
■ Artery of the pterygoid canal: Runs with deep petrosal and greater
petrosal nerves.
,Within the cranial cavity
3. Cavernous part:
○ Lies within cavernous sinus, covered by endothelium.
○ Travels from foramen lacerum → dorsum sellae → anterior clinoid process.
○ Emerges from dural roof of sinus under brain.
○ Branches:
■ Trigeminal ganglion branch.
■ Inferior hypophyseal artery → posterior lobe of pituitary gland.
■ Meningeal branches → anterior/middle cranial fossa + tentorium
cerebelli.
4. Cerebral part:
○ Lies in subarachnoid space.
○ Turns backward below optic nerve, then ascends to terminal branches.
○ Segments:
■ C5: Ascends to dorsum sellae.
■ C4: Turns forward along sphenoid body.
■ C3: Curves up to anterior clinoid process.
■ C2: Turns backward below optic nerve.
■ C1: Ascends to divide into terminal branches.
○ C5, C4, C3 = cavernous part.
○ C2, C1 = cerebral part.
○ C4 → C2 = forward convex U-turn = carotid siphon.
Branches of ICA Prior to Termination (Cerebral Part)
● Ophthalmic artery
● Superior hypophyseal artery
● Posterior communicating artery
● Anterior choroidal artery
Ophthalmic Artery
● Main branch of ICA (supplies all orbital structures).
● Course:
○ Enters orbit via optic canal (inferolateral to optic nerve).
○ Arches over optic nerve, then forwards on medial orbital wall.
Branches of Ophthalmic Artery
1. Central retinal artery:
○ Pierces optic nerve → supplies retina (anatomical end artery).
○ Occlusion → blindness.
2. Ciliary arteries (long, short, anterior):
○ Supply sclera, choroid, intraocular muscles.
, 3. Muscular branches:
○ Supply extraocular muscles, give rise to anterior ciliary arteries.
4. Lacrimal artery:
○ Lateral to optic nerve → supplies lacrimal gland + lateral eyelids (via lateral
palpebral).
5. Supraorbital artery:
○ Exits orbit via supraorbital foramen, supplies scalp.
6. Posterior ethmoidal artery:
○ Exits via posterior ethmoidal foramen → ethmoidal air cells, nasal septum
(upper part).
7. Anterior ethmoidal artery:
○ Exits via anterior ethmoidal foramen → ethmoidal air cells, frontal sinus,
anterior nasal septum.
8. Medial palpebral arteries:
○ Supply medial eyelids.
9. Dorsal nasal artery:
○ To dorsum of nose.
10. Supratrochlear artery:
● Forehead.
Terminal Branches of the ICA
● Anterior cerebral artery
● Middle cerebral artery
Anterior Cerebral Artery (ACA)
● Right and left ACAs connected by anterior communicating artery (completes anterior
circle of Willis).
● Segments:
○ A1: Precommunicating part.
○ A2: From anterior communicating to callosomarginal artery origin.
○ A3: Continuation = pericallosal artery.
Middle Cerebral Artery (MCA)
● Segments:
○ M1: Horizontal part (on sphenoid).
○ M2: Insular part (lateral sulcus).
○ M3: Opercular part (emerges from lateral sulcus).
○ M4: Cortical part.
, Anastomoses Between ICA and ECA
● Main sites: Scalp, nasal cavity, orbit.
Scalp
● Supraorbital artery (ICA) ↔ Frontal branch of superficial temporal artery (ECA).
● Rich blood supply = profuse bleeding, but rapid healing.
Nasal Cavity
● Little's area / Kiesselbach’s plexus:
○ Anterior ethmoidal artery (ICA) ↔
■ Posterior septal branch of sphenopalatine artery (maxillary, ECA)
■ Septal branch of superior labial artery (facial, ECA).
○ Common site of epistaxis (nosebleeds).
● Posterior ethmoidal artery (ICA) ↔ Posterior septal branch of sphenopalatine
artery (ECA):
○ Less common, more difficult to control bleeding.
Medial Orbital Margin
● Dorsal nasal artery (ICA) ↔
○ Angular artery, lateral nasal artery (facial, ECA).
Superior Orbital Fissure
● Recurrent meningeal branch of lacrimal artery (ICA) ↔
○ Anterior branch of middle meningeal artery (maxillary, ECA).
Brain Circulation and Coverings- Arteries of the Brain
Arterial Supply of the Brain
Supplied by Four Arteries
● A pair of internal carotid arteries (ICA)
● A pair of vertebral arteries
