Anastamoses between internal and external carotid arteries

Dr James Harvey et al.

Multiple, highly-variable anastamoses exist between the internal and external carotid arteries. These anastamoses may not be evident on non-invasive imaging or even catheter angiography, and may only be demonstrable with elevated intra-arterial pressures or high-flow states. ICA-ECA collaterals may enlarge following occlusion of the ICA and have been implicated in the development of dural AV fistulas.

A non-exhaustive list of sites include:

Orbit
- Ophthalmic artery (ICA) – middle meningeal artery (ECA)
- The ophthalmic artery most commonly arises from the supraclinoid (C6) segment of the ICA but may arise from the middle meningeal artery or middle cerebral artery
- Ophthalmic artery may have collaterals with the middle mengingeal artery or with the deep temporal artery or infraorbital artery (from the maxillary artery)
Cavernous sinus
- Inferolateral trunk (ICA) – branches of maxillary artery (ECA)
- The inferolateral trunk is a variably identified branch of the cavernous (C4) segment of the ICA. Branches of the inferolateral trunk may anastamose with the middle meningeal artery/deep temporal artery/artery of the foramen rotundum
Ethmoidal sinuses
- Anterior and posterior ethmoidal arteries (ICA) – sphenopalatine artery (ECA)
Nose
- Dorsal nasal artery (ICA) – nasal branches of the facial artery (ECA)
- Dorsal nasal artery is branch of the ophthalmic artery
- Recognition is important in epistaxis embolization
Scalp
- Superior orbital artery (ICA) – superficial temporal artery (ECA)
- The superior orbital artery is a branch of the ophthalmic artery

Collateral pathways are also present between the occipital artery (from the ECA) and muscular branches of the vertebral arteries around the C1 and C2 vertebrae.