15 - Defining the carotid sinus nerve: characterization and revised descriptive criteria

Poster Board Number: 15
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Co-authors:

Sophie Scherer - Anatomy - Case Western Reserve University School of Medicine; Brandon Brunsman - Anatomy - Case Western Reserve University School of Medicine; Leina Lunasco - Anatomy - Case Western Reserve University School of Medicine; Andrew Crofton - Anatomy - Case Western Reserve University School of Medicine

Abstract Body : Introduction:

The carotid sinus nerve (CSN) is a branch of cranial nerve (CN) IX with variable contributions from the cervical elements of CNs X-XII and the sympathetic chain. The CSN is a chief element of the intercarotid plexus and acts as the afferent limb of the baroreceptor reflex to relay sensory information from the carotid sinus and body. The high complexity and variability of the CSN make identification of the CSN difficult and can lead to nonspecific approaches to baroreflex activation therapy. We seek to provide a more anatomically detailed characterization of the structure and its variants through gross anatomic dissection and suggest descriptive criteria to facilitate accurate identification of nervous structures innervating the carotid sinus.



Methods:

Twenty-two CSNs were dissected from 15 cadavers. Distances from anatomic landmarks, course, and branching patterns were recorded.



Results:

The mean distances of the CSN’s origin off CN IX from key landmarks were: 11.18 ±6.73 mm to the jugular foramen, 13.33 ±5.75 mm to the distal styloid process, and 49.40 ±8.83 mm to the anterior margin of the tragus. The CSN most commonly descended along the anterolateral (7 of 13) surface of the right internal carotid artery (ICA) and the posterolateral (5 of 9) surface of the left ICA. The CSN emerged from two rami off CN IX in 3 specimens. The CSN received branches from the sympathetic chain in 36% of specimens, CN X in 18%, and CN XII in 5%. The CSN traveled alone in 32% of cases. The right side of a 76 year-old Caucasian male reveals independent branches from CN IX and X that both distributed to the carotid sinus, which demonstrates the difficulty in accurately identifying the CSN.



Conclusions:

The CSN frequently exhibits a wide variety of normal anatomic variants. To accurately identify the CSN versus distinct CN X-XII and sympathetic contributions to carotid sinus, we propose that such a nerve meet the following criteria: 1) maintain at least one point of origin off CN IX and 2) terminate at the carotid sinus. If those criteria are not met, the nerve should be classified as a carotid sinus branch of the nerve from which it originated.



Significance/Implications:

Our descriptions of the CSN can inform surgical approaches to the carotid bifurcation. Criteria for CSN identification can guide anatomists and clinicians and may clarify future literature. Together, these findings can establish a basis for further functional research of the CSN and inform the development of improved baroreflex activation therapies.