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Background: Left nonrecurrent laryngeal nerve (LNRLN) is an extremely rare anatomic variant. The development of such anatomic variation requires the regression of both the fourth (aortic arch) and sixth (ductus arteriosus, DA) arches on the left side. Preoperative prediction of this variant is difficult but might reduce risk of nerve injury., Methods: A 34-year-old female was indicated for thyroidectomy for a 2.4 cm follicular neoplasm and Graves' disease. Due to a positive medical history of 22q11.2 microdeletion and unexplained left vocal cord paralysis, a preoperative chest computed tomography (CT) scan was obtained and revealed a right-sided aorta (RSA) and aberrant left subclavian artery (ALSA) without Kommerell's diverticulum. A left-sided NRLN was then highly suspected., Results: Thyroidectomy was performed under general anesthesia with the utilization of intraoperative laryngeal nerve monitoring. A LNRLN was confirmed intraoperatively., Conclusions: Right-sided aorta and ALSA indicate embryologic regression of the left fourth primitive aortic arch. The absence of Kommerell's diverticulum at the origin of the ALSA indicates the lack of high-pressure blood flow from the pulmonary artery to the ALSA through the ductus arteriosus during embryogenesis, suggesting the embryologic regression of the left sixth primitive aortic arch. The presence of all 3 radiologic features thus highly suggests the possibility of a LNRLN.

The etiology of 389 cases of partial or complete bilateral abductor vocal cord paralysis has been determined and classified. One hundred and forty-nine were infants and children 12 years of age and under; 240 were adults, age 13 and older. In the infants and children the paralyses were congenital in 82 cases, of which 43 were associated with other congenital anomalies, and 39 were without associated anomalies. Fifty-nine cases were considered acquired, most being secondary to underlying congenital anomalies, particularly the associated findings of meningomyelocele, Arnold-Chiari malformation, and hydrocephalus. Eight cases of paralysis in this age group were of undetermined etiology. Of the 240 adult cases of bilateral vocal cord paralysis. 138 followed thyroidectomy. Fifty-two cases were associated with various neurologic disorders, including poliomyelitis, Parkinson's disease, cerebrovascular accident, Guillain-Barré syndrome, multiple sclerosis, neoplasms and other miscellaneous neurologic conditions. Sixteen cases were due to malignant neoplasms of the neck and mediastinum. The remaining 34 cases constitute a miscellaneous group which includes foreign bodies, bilateral neck dissection, infection, congenital lesions, trauma, and idiopathic paralyses. The characteristic symptoms of bilateral abductor vocal cord paralysis include normal or near normal phonation with inspiratory stridor which may progress to complete respiratory obstruction. These symptoms are due to the stationary but flaccid midline position of the vocal cords which places them in a phonating position, where they both obstruct the airway and produce a faily clear voice or cry. This paradoxical combination of symptoms was frequently found to be responsible for a failure or delay in diagnosis.