Carotid space

Last revised by Bálint Botz on 12 Feb 2020

The carotid space, the suprahyoid portion of which is also known as the poststyloid parapharyngeal space, is a deep compartment of the head and neck bound by the carotid sheath.

The "carotid space" terminology was introduced by some radiologists to facilitate differential diagnosis and is used in this article 1. However, in much of the surgical and anatomical literature, the carotid space within the suprahyoid neck is considered part of the parapharyngeal space 2,3. Under this nomenclature, the parapharyngeal space is divided into prestyloid and poststyloid (retrostyloid) compartments by the tensor-vascular-styloid fascia 9. The poststyloid parapharyngeal space consists of or includes the carotid space or sheath around the cervical internal carotid artery.

The carotid space is a roughly cylindrical space that extends from the skull base through to the aortic arch. It is circumscribed by the carotid sheath, which has contributions from all three layers of the deep cervical fascia 4. Above the carotid bifurcation, the contribution of the middle layer of cervical fascia can be inconsistent 9, and the sheath is interrupted 10.

The carotid artery bifurcation occurs near the level of the hyoid bone 1.

Suprahyoid carotid space:

The suprahyoid portion of the carotid space is synonymous with the poststyloid compartment of the parapharyngeal space.

Infrahyoid carotid space:

The carotid sheath is made from the various regional fascia, including contributions from all three layers of the deep cervical fascia 2:

Ultrasound is good for identifying vascular structures in the lateral neck.  The origin of the internal and external carotid arteries is the main point of sonographic interest as the carotid space superior to this cannot be visualized due to the mastoid process.  

The internal carotid is usually posterolateral to the external carotid however in 5-10% of the population the internal carotid lies medial or anterior or the two vessels may lie within the same frontal plane 5.

The external carotid can be identified from the internal carotid as:

  • it branches within the neck; the first immediate branch is the superior thyroid artery
  • Doppler tracing of vessel flow within the internal carotid is typical of low peripheral resistance (high diastolic peak), whereas the external carotid has high-resistance flow (lower diastolic peak, systolic peak higher than that of the internal carotid) 5
  • often modality of choice when evaluating for pathology within the carotid space because CT is able to identify any benign or malignant tumors within the carotid space and allows for better visualization of any associated bone involvement in comparison to MRI
  • best identifies vascular lesions on CT angiography 6
  • useful for identifying between the different types of benign tumors involving the carotid space
  • provides better soft tissue contrast in comparison to CT and can be useful at elucidating any signs of intramural metastatic nodal invasion of the carotid artery which is a relative contraindication for surgical tumor resection 6

A mass originating from the carotid space will cause anterior displacement of the parapharyngeal space fat. Lesions include 7:

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