IATROGENIC
INJURY TO THE SPINAL ACCESSORY NERVE
INTRODUCTION:
The accessory nerve (cranial nerve 11) is one of the 12 paired cranial nerves - nerves which arise directly from the brain. The cranial nerves are distinguished from the 31-paired spinal nerves, which originate from the spinal cord. The accessory nerve is unique in that it is formed by the fusion of cranial and spinal root components. Nonetheless, the two components are viewed as a cranial nerve. (1)
The joined cranial and spinal components exit the skull through the jugular foramen, then separate. The cranial component joins the vagus nerve while the spinal component travels on as the spinal accessory nerve (SAN). (1,2)
In the neck, the SAN descends in close proximity to the internal jugular vein. It passes through or posterior to the sternocleidomastoid muscle (SCM), which it innervates. The SAN then enters the posterior triangle of the neck at the junction of the upper and middle thirds of the SCM. It travels obliquely on the surface of the levator scapulae until it reaches the trapezius at the junction of its middle and lower thirds. (2,3,4)
In the posterior triangle, the nerve is very superficial - within 1 to 1.5 cm of the skin surface. It is in this location that the nerve is most susceptible to iatrogenic injury. (2,3)
CASE
PRESENTATION:
A 43-year old female dental hygienist was seen by a General Surgeon for an infected sebaceous cyst located in the right posterior triangle of the neck. The surgeon initially treated her with antibiotics. After 1 week, he excised the cyst since the abscess had not resolved. The surgery was performed under general anesthesia without use of a nerve stimulator. The specimen showed an infected epidermoid cyst with severe surrounding inflammation. The specimen dimensions were 4.1 cm x 1.5 cm with a depth of 1.5 cm.
Following the surgery, the patient experienced severe pain in the right shoulder with sagging and decreased range of movement. She was unable to return to work because of the symptoms. She saw her surgeon for these symptoms who noted that the patient was able to shrug her shoulders. He reassured the patient that her symptoms were secondary to healing and would resolve with time.
The patient saw her surgeon two times more for the same symptoms over the following 6 months. No further studies were performed. She continued to be disabled and the surgeon suspected that she might be malingering. Finally, after 8 months, she saw a Neurologist. An EMG showed denervation of the trapezius. At this time, the right trapezius was wasted and there was significant drooping of the right shoulder. The patient had severe weakness of shoulder abduction.
After referral to a Plastic Surgeon, the wound was re-explored and a 3 cm segment of the SAN was found to be missing. A sural nerve graft was performed, but the patient never recovered significant trapezius function. She was unable to return to her work as a dental hygienist.
The patient initiated a lawsuit against the surgeon who was ultimately found negligent for injuring the nerve and failing to diagnose the problem. The case was settled for $250,000.
DISCUSSION:
Injury
to the SAN is not trivial - it causes significant pain and decreased range of
motion of the shoulder and is often permanently disabling.
Iatrogenic injury is the most common injury of the SAN.
As a result of its superficial location in the posterior triangle, the
SAN is susceptible to injury during any procedure in this area - the most common
being lymph node biopsy. (2)
Before
and after any procedure in the posterior triangle, it is critical to evaluate
the function of the SAN. The ability
to shrug an affected shoulder, however, is an inadequate test of accessory nerve
and shoulder function. The levator
scapulae can elevate the shoulder in the absence of a functioning trapezius.
Testing needs to be done with the arm abducted at 90 degrees so that the
humerus is fixed on the acromion. Shoulder
movement beyond this point requires a functioning trapezius.
(1,3)
In
the unfortunate event of an injury to the SAN, early recognition is critical
since studies have shown that repair within 3 months yields good results, but
longer delays are associated with poor outcomes.
(1,3)
CONCLUSION:
The
medico-legal implications of SAN injury are obvious.
Iatrogenic injury to the SAN is preventable.
Lymph nodes in the posterior triangle should be approached with caution,
as should any procedure in this area. If
surgery is determined to be necessary, a nerve stimulator can help avoid injury
or if necessary, the nerve can be identified and avoided.
Finally, it is imperative to diagnose injuries early through physical
examination and EMG studies. Early
diagnosis can lead to successful nerve repair and return of function.
(1)
REFERENCES:
1. Williams, PL, The Anatomical Basis of Medicine & Surgery. Gray's Anatomy. 1995;Edition 38, Saunders W B Co.
2.
3.
Donner, TR, Kline, DG, Extracranial Spinal Accessory Nerve Injury.
Neurosurgery, Vol. 32, No. 6, 1993.
Nason, RW, Abdulrauf, BM, Stranc, MF, The Anatomy of the Accessory Nerve
and Cervical Lymph Node Biopsy. The
American Journal of Surgery, Vol. 180, 2000.
ABOUT: Brian Camazine, M. D.