Related Experiment Video
Updated: Jun 19, 2026

Modified Radical Neck Dissection for Cervical Metastasis
Published on: February 20, 2026
Anatomical variations of the spinal accessory nerve and its relevance to level IIb lymph nodes
Sang Hyuk Lee1, Jong Kyu Lee, Sung Min Jin
1Department of Otorhinolaryngology-Head and Neck Surgery, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
Objective:
This study was conducted to identify anatomical variations of the spinal accessory nerve (SAN) in the upper neck, the landmark of the anterior and inferior border of level IIb, and to evaluate the nerve's effect on the border and the number of lymph nodes (LNs) in level IIb.
Study Design And Setting:
Case series with planned data collection.
Subjects And Methods:
A total of 181 neck dissections (NDs) were prospectively enrolled in this study. The relation between the SAN and adjacent structures (internal jugular vein [IJV], sternocleidomastoid muscle [SCM], cervical plexus) and the number of LNs in level IIb was investigated.
Results:
The SAN crossed the IJV ventrally in 72 cases (39.8%) and dorsally in 104 cases (57.4%), and passed through the IJV in five cases (2.8%). The SAN ran along the inner surface of the SCM and sent branches to the SCM without penetration of the muscle in 83 cases (45.9%), whereas in 98 cases (54.1%) the nerve sent branches to the SCM by penetration. Cervical plexus contribution to the SAN was seen from C2 in 96 cases (53.1%), C2 and C3 in 69 cases (38.1%), and C3 in 16 cases (8.8%). The mean number of LNs of level IIa and level IIb was 6.5 and 8.2 in cases in which the SAN crossed the IJV ventrally, and 6.8 and 5.4 in dorsally crossing cases. LNs included in the neck level IIb in ventrally crossing SAN cases were significantly larger than the dorsally crossing cases (P < 0.05).
Conclusions:
Our results may help to minimize the incidence of injuring the SAN in the upper neck during ND. Neck level IIb would contain more LNs if the course of the nerve leans toward the ventral side.
Related Concept Videos
Spinal Nerves: Plexus I
The Cervical Plexus
The cervical plexus, formed by the anterior rami of the first four...
Spinal Nerves: Anatomy
There are 31 bilateral pairs of spinal nerves, each emerging from the spinal cord through the intervertebral foramina—openings between adjacent vertebrae. These nerves are...
Detailed Structure and Function of Lymph Nodes
From a histological perspective, lymph nodes can be split into two main areas: the superficial cortex and the deep medulla. The outer cortex is populated by dendritic cells, macrophages, and B lymphocytes, which are densely packed into follicles. When these B-lymphocytes are presented...
Muscles that Move the Head
The bilateral sternocleidomastoid, or SCM, and the suprahyoid and infrahyoid muscles are significant head flexors. The SCM muscles originate at the sternum and clavicle and attach to the mastoid process of the temporal bone. The SCM contracts bilaterally to bend the head forward, whereas...
Sympathetic Pathways: Sympathetic Chain Ganglia
The Spinal Cord
