Abstract
Purpose
Conflicting locations of the spinal accessory nerve (SAN) with respect to the internal jugular vein (IJV) are reported in the literature and anatomy texts. The objective of this study is to analyze this anatomic relationship specifically at the level of the posterior belly of the digastric muscle where it is encountered most often during surgery.
Material and Methods
This study is a case series with planned chart review of all operative reports for neck dissections/explorations performed between June 2002 to June 2008 at an academic tertiary care referral center. Inclusion criteria required intraoperative identification of the SAN at the level of the posterior belly of the digastric muscle. Patients undergoing revision neck dissection were excluded. Data is presented using descriptive statistics.
Results
One hundred ninety-seven patients were identified; 175 met inclusion criteria. Thirty-two patients received bilateral neck dissections/explorations, resulting in a total of 207 SANs for analysis. The most common location of the SAN was lateral to the IJV (198; 95%). In 6 (2.8%) cases the SAN was identified medial to the IJV and 2 nerves pierced the IJV. A new variant of the SAN splitting around the SAN was identified.
Conclusion
The majority of SANs course lateral to the IJV at the level of the posterior belly of the digastrics muscle (95%). This intraoperative finding differs from cadaveric studies. Discrepancies may reflect variation in the level at which the nerve was identified, as well as tissue changes related to cadaver versus in vivo studies.
1
Introduction
To date, descriptions of spinal accessory nerve (SAN) anatomy in relation to the internal jugular vein (IJV) have varied widely in the literature . Anatomists such as Hollingshead, Grant, and Netter depict the typical course of the SAN at the level of the posterior belly of the digastric muscle as passing lateral and anterior to the IJV , while others depict a posterior course . An equal preponderance of the lateral and medial course , along with a third variant in which the SAN passes through a fenestration of the IJV , have all been reported.
In order to avoid the morbidity associate with SAN injury, it is critical for surgeons operating in the neck to understand the location of the nerve, as well as anatomic variations which may be encountered. The purpose of this investigation was to identify the intraoperative relationship of the SAN to the IJV in patients undergoing neck dissection and neck exploration. The second objective was to identify and determine the occurrence of each SAN variation at the level of the posterior belly of the digastric muscle, where the surgeon is most likely to encounter the structure during routine dissection.
2
Methods
The University of Texas Health Science Center at San Antonio Internal Review Board approval was obtained. This study entailed a case series with planned review conducted of all patients undergoing neck dissection/exploration at our institution from June 2002 to June 2008. The senior surgeon’s (FRM) surgical log was reviewed to identify all cases meeting inclusion criteria. Patients were excluded from study if they had previously undergone external beam radiation or neck dissection due to potential scarring which could alter the location of the SAN. The operative report from each case was reviewed in order to identify the location of the SAN with respect to the IJV specifically at the posterior belly of the digastric muscle. The majority of cases had this anatomic relationship recorded as part of larger study investigating lymph node distribution in Levels IIA and IIB. The location of the SAN was labeled as: lateral (superficial; ventral) to the IJV, medial (deep; dorsal) to the IJV, traversing the IJV, and dividing around the IJV. The nerve was considered traversing the vein when it tracked through the lumen of the IJV ( Fig. 1 ). The divided spinal accessory nerve was defined as having two branches traveling both superficial and deep to the IJV. All cases in which the intraoperative location of the SAN at the level of the digastric could not be ascertained were excluded from study.
2
Methods
The University of Texas Health Science Center at San Antonio Internal Review Board approval was obtained. This study entailed a case series with planned review conducted of all patients undergoing neck dissection/exploration at our institution from June 2002 to June 2008. The senior surgeon’s (FRM) surgical log was reviewed to identify all cases meeting inclusion criteria. Patients were excluded from study if they had previously undergone external beam radiation or neck dissection due to potential scarring which could alter the location of the SAN. The operative report from each case was reviewed in order to identify the location of the SAN with respect to the IJV specifically at the posterior belly of the digastric muscle. The majority of cases had this anatomic relationship recorded as part of larger study investigating lymph node distribution in Levels IIA and IIB. The location of the SAN was labeled as: lateral (superficial; ventral) to the IJV, medial (deep; dorsal) to the IJV, traversing the IJV, and dividing around the IJV. The nerve was considered traversing the vein when it tracked through the lumen of the IJV ( Fig. 1 ). The divided spinal accessory nerve was defined as having two branches traveling both superficial and deep to the IJV. All cases in which the intraoperative location of the SAN at the level of the digastric could not be ascertained were excluded from study.
