Anatomical variations of the spinal accessory nerve and its relevance to level IIb lymph nodes.
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.


METHODS
Case series with planned data collection.


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.
Department of Otorhinolaryngology-Head and Neck Surgery, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
Sang Hyuk
SH
Lee
Jong Kyu
JK
Lee
Sung Min
SM
Jin
Jin Hwan
JH
Kim
Il Seok
IS
Park
Hyung Ro
HR
Chu
Hwoe Young
HY
Ahn
Young Soo
YS
Rho
D000055:Accessory Nerve / Q000033:anatomy & histology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006258:Head and Neck Neoplasms / Q000601:surgery; D006801:Humans; D008198:Lymph Nodes / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000601:surgery; D037981:Neck Dissection