Normal and Varied Anatomy of Spinal Accessory Nerve and its Clinical Implications
Rajani Singh *
Department of Anatomy, Graphic Era Institute of Medical Sciences, Chakarata Road, Doolkot 248007, Dehradun, India.
Kavita Gupta
Department of Physiology, Graphic Era Institute of Medical Sciences, Chakarata Road, Doolkot 248007, Dehradun, India.
Neeru Garg
Department of Physiology, Graphic Era Institute of Medical Sciences, Chakarata Road, Doolkot 248007, Dehradun, India.
*Author to whom correspondence should be addressed.
Abstract
There are twelve cranial nerves, and the spinal accessory nerve is the XI cranial nerve, innervating the sternocleidomastoid and trapezius muscles. The nerve under study arises from a nucleus in the spinal cord and emerges as a variable number of twigs attached to the spinal cord; later, it fuses with the cranial root, which originates in the medulla. It enters the cranial cavity through the foramen magnum and exits through the jugular foramen. Outside the cranial cavity, this nerve passes superficial to the jugular vein. In the posterior triangle, it makes several connections and terminates in the trapezius muscle. The inclusion of this nerve among the cranial nerves is controversial, as it is often subject to non-union with the cranial twig. Moreover, the nerve under consideration varies anatomically, and lack of awareness of this variation may place neurosurgeons in difficulty when planning the diagnosis and management of medical conditions related to this nerve. In this chapter, the normal and varied anatomy of this nerve is highlighted, and its associated implications are discussed to help clinicians treat related medical conditions with minimal risk. The aim of the study is to underscore the importance of the spinal accessory nerve, and this information will be useful for neurosurgeons, anatomists, otolaryngologists and clinicians involved in head and neck interventions in related areas with fewer complications.
The literature was scrutinised using different online databases, such as ResearchGate, SciELO, MEDLINE, PubMed, PubMed Central and Google Scholar. The results of the literature search were interpreted, analysed and discussed.
The literature survey revealed that the SpA travelled superficial to the internal jugular vein in most cases (about eighty-seven percent), whereas in the remaining eleven percent of specimens, the spinal accessory nerve was detected deep to the internal jugular vein. Some authors and investigators observed this nerve passing superficial to the internal jugular vein in 51.4% of individuals. The aforementioned studies emphasised that clinicians should be cautious while performing surgery in the region of the jugular foramen.
Keywords: Cranial nerve, cranial cavity, varied anatomy, accessory nerve, spinal cord