Restriction lift date: 2027-09-11
Distal course and variability of the spinal accessory nerve: a cadaveric study with surgical implications
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Date
2026-09-11
Authors
Stasiewicz, Martyna
O’Flynn, Carrie
Hand, Collette K.
Toulouse, André
Journal Title
Journal ISSN
Volume Title
Publisher
Springer-Verlag Italia s.r.l.
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Abstract
Purpose: The spinal accessory nerve (SAN) is most vulnerable to injury along its distal extracranial course in the posterior cervical triangle. While proximal anatomy is well described, distal branching patterns and cervical plexus contributions to trapezius innervation remain poorly defined. This study aimed to characterise distal extracranial SAN branching and cervical plexus contributions and to assess whether proximal configurations predict distal trapezial innervation. Methods: Ten sides from five adult cadavers were dissected from the emergence of the SAN at the posterior border of the sternocleidomastoid muscle (SCM) to its intramuscular termination in the trapezius. Emergence level, SCM branching pattern (Shiozaki classification), cervical plexus communications, loop formations, and distal branching were recorded. Linear morphometric measurements were obtained where feasible. Results: The SAN entered the posterior cervical triangle at variable levels (4.5–8.5 cm from the mastoid). Only Shiozaki Type A and B SCM patterns were identified. Cervical plexus contributions were present in all specimens. An independent cervical branch to the superior trapezius occurred in 6/10 sides, and SAN-cervical loop formation in 2/10 sides. Distal intramuscular branching ranged from two to five terminal branches, with no clear relationship to proximal configuration or measurements. Conclusion: Distal SAN anatomy is highly variable and cannot be predicted from proximal patterns or surface landmarks alone, underscoring the need for meticulous identification of both the SAN and cervical contributions during posterior cervical triangle and trapezius-based surgery.
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Keywords
Anatomical variation , Cervical plexus contribution , Posterior cervical triangle , Spinal accessory nerve , Trapezius muscle , [Medicine]
Citation
Stasiewicz, M, O’Flynn, C, Hand, C K & Toulouse, A 2026, 'Distal course and variability of the spinal accessory nerve: a cadaveric study with surgical implications', Surgical and Radiologic Anatomy, vol. 48, no. 1, 227, pp. 1-10. https://doi.org/10.1007/s00276-026-03994-9
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© 2026, the Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature. This version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://link.springer.com/article/10.1007/s00276-026-03994-9#Abs1