Anatomic relationship between the spinal accessory nerve and the jugular vein: a cadaveric study

Area of Science:

• Anatomy
• Neurosurgery
• Surgical Anatomy

Background:

• Conflicting results exist regarding the Spinal Accessory Nerve (SAN) and Internal Jugular Vein (IJV) relationship due to limited specimens and anatomical variability.
• Classic teaching states the SAN almost always crosses the IJV anteriorly, but posterior crossings necessitate surgical caution to prevent IJV injury.

Purpose of the Study:

• To characterize the anatomical relationship of the SAN to the IJV at the jugular foramen (JF), base of skull (BoS), and posterior belly of the digastric muscle.
• To measure the SAN's distance from the BoS to its crossing of the IJV.
• To describe the anatomy of the JF, including its dimensions and partitioning.

Main Methods:

• Dissection of 84 necks from 61 cadavers (27 male, 34 female).
• Recording the SAN-IJV relationship at the JF (intracranial view), exiting the JF at the BoS, and at the posterior belly of the digastric muscle.
• Measuring the SAN's path length from BoS to IJV crossing, and JF dimensions and partitioning.

Main Results:

• The SAN traveled anteromedial to the IJV within the JF in 87% of cases.
• Exiting the JF, the SAN was lateral to the IJV in 67% of necks.
• In the anterior neck, the SAN crossed the IJV anteriorly in 80% and posteriorly in 19% of cases. Average SAN path length from BoS to IJV crossing was 2.38 cm. JF dimensions averaged 1.42 cm (length) x 0.78 cm (width), with 36% of JFs partitioned.

Conclusions:

• While the SAN predominantly crosses the IJV anteriorly in the neck, posterior crossings are not uncommon, emphasizing the need for surgical awareness of anatomical variations.
• The measured distance of the SAN from the BoS to the IJV crossing can aid surgeons in locating the nerve during dissections.
• No correlation was found between JF anatomy and the SAN-IJV relationship, nor between the SAN-IJV relationship at different anatomical points.