Anastamoses between internal and external carotid arteries
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Multiple, highly-variable anastomoses exist between the internal and external carotid arteries. These anastomoses 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.
A non-exhaustive list of such sites includes:
- ophthalmic artery (ICA) – middle meningeal artery (ECA) 1
- 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 meningeal artery or with the deep temporal artery or infraorbital artery (from the maxillary artery)
- ethmoidal sinuses
- inferolateral trunk (ICA) – branches of maxillary artery (ECA) 1
- the inferolateral trunk is a variably identified branch of the cavernous (C4) segment of the ICA. Branches of the inferolateral trunk may anastomose with the middle meningeal artery/deep temporal artery/artery of the foramen rotundum 1.
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 1.