Trapezius muscle branch of the spinal accessory nerve without penetrating the sternocleidomastoid muscle as a pitfall in neck dissection: prevalence in a Japanese institution and a protocol for the prevention of iatrogenic injury

Abstract

Background

The spinal accessory nerve (SAN) has several anatomical variations, which may be a pitfall in neck dissection (ND). These include the trapezius muscle branch (TB), which stems from the common trunk before entering the sternocleidomastoid muscle (SCM).

Aims/Objectives

To investigate the prevalence of this variation and suggest a protocol for preventing unexpected injury of the TB in ND.

Materials and methods

We conducted a retrospective cohort study for 93 patients who had undergone neck dissection (117 sides) without resection of the SCM nor SAN. We recorded the division of the TB after and before penetration of the SCM by the common trunk (penetrating type TB [PTB]) and non-penetrating type TB [NPTB], respectively).

Results

Among NDs, PTB and NPTB were observed in 61 (52%) and 56 (48%) sides, respectively. In the subgroup of 24 cases with bilateral ND, PTB/PTB, NPTB/NPTB, and NPTB/PTB were observed in eight (33%), nine (38%), and seven (29%) cases, respectively. The prevalence of PTB/NPTB did not differ according to age, sex, or laterality.

Conclusions and significance

NPTB is a common anatomical variation. The presence or absence of a branch from the common trunk must be initially checked to avoid unexpected damage to the TB.

Chinese abstract

背景：脊髓副神经 (SAN) 有若干种解剖学变体, 这可能是颈部解剖 (ND) 的一个难点。这些变体包括斜方肌分支 (TB), 它自主干进入胸锁乳突肌 (SCM) 。

目的：调查这种变体的发生情况并提出一种预防ND 过程中 TB 意外损伤的方案。

材料和方法：我们对 93 名接受颈部解剖（117 侧）但未切割 SCM 或 SAN 的患者进行了一项回顾性队列研究。我们记录了主干穿透 SCM 前后的 TB的区别（穿透型 TB [PTB]）和非穿透型 TB [NPTB]）。

结果：在ND过程中, 分别在61侧（52%）和56侧（48%）观察到PTB和NPTB。在24例双侧ND中, PTB/PTB、NPTB/NPTB、NPTB/PTB分别为八（33%）、九（38%）和七（29%）个病例。 PTB/NPTB 的患病率不因年龄、性别或偏侧而异。

结论和意义：NPTB是一种常见的解剖变异。必须首先检查来自主干的分支的存在与否, 以免对 TB 造成意外损坏。

Keywords:

• Neck dissection
• spinal accessory nerve
• trapezius branch
• non-penetrating type
• anatomical variations

Acknowledgement

The authors thank Enago for English language editing.

Disclosure statement

No potential conflict of interest was reported by the author(s).