recurrent laryngeal nerve ( rln ) palsy is one of the most common complications after thyroid surgery .
therefore , reducing the rate of temporary and , especially , permanent nerve palsy is essential .
although an important anatomic landmark , zuckerkandls tubercles , could help us to locate and dissect the rln during thyroid surgery , anatomic variations such as nonrecurrent laryngeal nerve ( nrln ) might increase the rate of rln damage .
nrln is a rare anomaly that represents a major risk factor for injury during neck surgery .
because of its special anatomical position , it may be misdiagnosed and damaged , with subsequent vocal cord paralysis that can decrease the overall physical and psychological quality of life .
vascular anomaly of the aortic arches during early embryonic development results in the formation of nrln , which was first reported by stedman in 1823 .
the absence of brachiocephalic artery and the presence of an aberrant right subclavian artery ( arteria lusoria ) is the feature used to identify nrln .
surgeons seek ways to make a preoperative diagnosis of nrln to reduce the risk of inadvertent nerve injury .
the aim of this study was to retrospectively analyze the methods of preoperative judgment and intraoperative identification and protection of nrln during thyroidectomy or parathyroidectomy .
of the 7169 patients who underwent thyroidectomy or parathyroidectomy at our hospital between august 2008 and january 2013 , 5 patients who had nrln were included in this study .
preoperative chest x - rays , neck ultrasonography ( us ) , and ct findings were reviewed . due to the cost , ct scans were mainly performed for the patients with suspected malignancy and lymph node metastasis .
the study was approved by the ethics committee at our hospital . due to embryologic reasons ,
nrln is always associated with vascular anomalies of the aortic arch . on the right side , the absence of brachiocephalic artery and the presence of an 
arteria lusoria  is the feature used to identify nrln . in ct scan images , the  arteria lusoria  was identified as an aberrant right subclavian artery that originated from the left part of the aortic arch , crossed the mediastinum behind the esophagus , and entered the right base of the neck .
the diagnosis of  arteria lusoria  was rejected when the brachiocephalic artery was found . in the us
scans , the division of the brachiocephalic artery into the right common carotid artery and the right subclavian artery has been described as the  y sign  ( figure 1a ) . according to the intraoperative findings ,
type i arises directly from the vagus nerve and running along with the superior thyroid vessels ; type iia originates from the vagus on the level of the trunk of inferior thyroid artery ; and type iib originate from the vagus and travels under the level of the trunk of inferior thyroid artery or between the branches .
we retrospectively reviewed patient information , including clinical presentation , physical examination , diagnostic investigations , therapeutic interventions , and pathology results .
the normal preoperative vocal cord function of all patients were confirmed by fibrolaryngoscope , and none of them presented symptoms related to recurrent laryngeal nerve , such as hoarseness or bucking . in our group , near total thyroidectomy was performed in 2 patients , right lobectomy was performed in 2 patients , and subtotal thyroidectomy was performed in 1 patient .
the postoperative histopathological diagnosis included 3 papillary carcinomas , 1 follicular carcinoma , and 1 nodular goiter ( table 1 ) .
all of the 5 patients received preoperative chest x - ray , us , and ct imaging .
we retrospectively reviewed the chest x - ray , us , and ct results . in our study , patients with nrln had lacked the brachiocephalic trunk and had an  arteria lusoria  on ct images .
the right subclavian artery originated directly from the left side of aortic arch , crossed the mediastinum behind the esophagus , and entered to the right side of the neck ( figure 2 ) .
we found no features of chest x - ray and us results to identify the nrln before surgery .
however , by reviewing the us images , we found that the right common carotid artery originated directly from the aortic arch and separated from the right subclavian artery , and the brachiocephalic truck was absent ( figure 1b ) .
all surgical procedures of the 5 patients were performed by experienced surgeons . when a preoperative  arteria lusoria
 diagnosis was given by ct findings , the surgical procedure of nrln identification was performed .
after dissection of the upper pole , we gently mobilized the thyroid inherent capsule , dissected the middle cervical vein and the inferior thyroid vessels , isolated and mobilized the thyroid lobe , and pulled it to the left .
nrln was found on the level of the inferior thyroid artery or cartilage and entered into the larynx at its usual location ( figure 3 ) . in searching for the normal recurrent laryngeal nerve
careful intraoperative dissection also allowed for detection of nrln in cases not detected by preoperative ct scan .
the nerve wraps around the sixth arch in the normal embryo stage . on the right ,
the nerve moves up as high as the fourth arch , which forms a portion of the subclavian artery . in the absence of the fourth aortic arch ,
the right recurrent laryngeal nerve goes directly into the larynx , forming a right nrln .
because the formation needs the coexistence of situs inversus viscerum , left nrln is extremely rare , with an incidence of 0.04% .
the detection rate of arteria lusoria by ct for the prediction of nrln was 0.4% ( 5/1170 ) in our group .
nrln protection without recognition before surgery is very difficult for the surgeon . if the abnormal vasculature is identified , the risk of nrln damage is reduced . in our group , although the vascular anomaly was recognized in preoperative neck ct findings , we also carefully explored the origin trunk of nrln after we identified it .
the tissue between the thyroid lobe and the carotid sheath was bluntly isolated , not dissected directly , to expose all the structure originating from the vagus nerve up to the larynx .
nrln includes 3 types based on the running course , of which type iia is the most common . in the present study ,
several imaging methods aimed at the preoperative identification of nrln have been recommended , including chest x - rays , barium esophagogram , vagal neurostimulation , and us and ct examinations .
each procedure has limitations because of the variable diagnostic accuracy , cost , and invasiveness .
chest x - rays may present a special linear shadow on the frontal view and a rounded image travelling upward and right from the top of the aortic arch , but these features exist in less than 20% of cases .
barium esophagogram may present an extrinsic compression on the left edge of the posterior esophagus notch at the third thoracic vertebral level below the aortic arch , which is called the  bayonet sign  .
because the sign can be easily missed if the superior thoracic esophagus is not carefully examined and the lateral or oblique views are not obtained , we recommend barium esophagogram only for dysphagic cases .
brauckhoff et al .   reported that selective vagal neurostimulation is an easy and reliable method to identify nrln .
they showed that a latency threshold of 3.5 ms after ipsilateral vagus nerve stimulation was able to distinguish between nrln and recurrent laryngeal nerve ( rln ) .
however , the lack of a standard with which to estimate variability and the high false positive results limit the use of this method .
us is an easy to perform , cost - effective , and noninvasive technique for preoperative recognition of nrln .
maurizio et al .   reported that us can easily identify the absence of the brachiocephalic trunk and indirectly predicts nrln with 100% accuracy .
its main limitation is that the results of us examinations depend on the sonographer ; if the us operator does not look for the  y sign  , nrln can not be predicted in routine preoperative us examination .
they are often performed to evaluate thyroid cancers with lymph node metastasis , intrathoracic goiters , or hyperparathyroidism . for diagnosis of 
nrln can be accurately predicted before surgery using ct by identifying the  arteria lusoria  and the absence of the brachiocephalic trunk without additional examination .
arteria lusoria  in ct images . in another study , although only 5 of the 20 patients with nrln were suspected before surgery , all patients had the  arteria lusoria  feature found by reviewing the ct images in after the operation .
in our experience , preoperative ct scanning is a simple and effective method for identifying abnormal vasculature to indirectly predict nrln .
combining ct and us findings with careful and systematic dissection of the rln area may help reduce the risk of nerve damage and prevent nerve palsy .
 backgroundnonrecurrent laryngeal nerve ( nrln ) is a risk factor for nerve injury during thyroidectomy or parathyroidectomy . 
 it is usually associated with abnormal vasculature that can be identified by several imaging methods . 
 the aim of this study was to retrospectively analyze the preoperative diagnosis and intraoperative protection of nrln.material/methodsof the 7169 patients who underwent thyroid surgery at our hospital between august 2008 and january 2013 , 5 patients with nrln were identified . 
 preoperative chest x - rays , neck ultrasonography ( us ) , and computed tomography ( ct ) findings were reviewed . 
 nrlns were carefully and systematically searched for in surgery.resultspreoperative ct predicted nrln in all 5 cases ( 100% accuracy ) . 
 the detection rate of nrln by ct was 0.4% ( 5/1170 ) . 
 nrlns were confirmed in surgery . 
 all of them were right - sided nrln with type iia variant . 
 the ct scans clearly revealed the vascular anomalies . 
 the review of us images suggested that vascular anomalies could be identified on the images in 1 patient . 
 no postoperative complications occurred in any patient.conclusionsthe preoperative ct scan was a reliable and effective method for identifying abnormal vasculature to indirectly predict nrln . 
 combining the ct and us findings with adequate surgical technique may help to reduce the risk of nerve damage , in addition to preventing nerve palsy . 
Background
Material and Methods
Results
Discussion
Conclusions