What is the Left Carotid Bifurcation?
The left carotid bifurcation is the anatomical point where the left common carotid artery divides into two branches: the internal carotid artery (which supplies blood to the brain) and the external carotid artery (which supplies the face, scalp, and neck). 1
Anatomical Location and Structure
The carotid bifurcation typically occurs at the level of the thyroid cartilage (Adam's apple), corresponding to approximately the C3-4 vertebral level. 1
The bifurcation includes a dilated portion called the carotid bulb, which extends superiorly for approximately 2 cm from the division point. 1
The superior extent of the bifurcation begins at the flow divider (the precise point where blood flow splits between the internal and external carotid arteries), while the inferior aspect starts at the beginning of the dilatation associated with the bifurcation. 1
Standardized Measurement Definitions
In clinical research and imaging protocols, the carotid bifurcation segment is defined as beginning at the tip of the flow divider and extending 8 mm proximally (downward toward the heart). 1
The common carotid artery is defined as the segment 10 mm below the bulb, while the internal carotid artery is defined as 10 mm above the flow divider. 1
Clinical Significance
The carotid bifurcation is the preferred site for atherosclerotic plaque development due to complex hemodynamic forces and turbulent blood flow patterns at this location. 2
This region is commonly assessed using ultrasound imaging to measure intimal-medial thickness (cIMT) for cardiovascular risk assessment. 1
The bifurcation can be adequately imaged in 68% to 82% of patients during carotid ultrasound examinations. 1
Anatomical Variations
While the typical bifurcation occurs at the thyroid cartilage level, anomalous bifurcations may occur up to 5 cm higher or lower than the standard location. 1
The left carotid bifurcation is typically positioned slightly higher in the neck compared to the right side. 2
Rare variations include intrathoracic bifurcation (within the chest cavity) or unusually high bifurcations, which have surgical implications. 3, 4
Distinguishing the Branches
- Doppler ultrasound can distinguish the internal from external carotid arteries: the internal carotid exhibits a more pulsatile flow pattern, while the external carotid shows continuous diastolic flow between systolic pulses. 1