The vocal cords play a crucial role in phonation. The muscles that are responsible for vocal cord movement are mainly innervated by the recurrent laryngeal nerves. The recurrent laryngeal nerves are branches of the vagal nerves. Vocal cord paralysis (VCP) can therefore be caused by any lesion along the course of the vagal nerves above the branching of the recurrent laryngeal nerves or of the recurrent laryngeal nerves itself. An offending lesion located in the brainstem or the skull base usually results in multiple cranial nerve deficits because at this level the vagal nerve is intimately related to other cranial nerves. Pathology involving the recurrent laryngeal nerves and/or the extracranial vagal nerves frequently results in isolated laryngeal symptoms. VCP most frequently affects one side but can be bilateral. Due to long anatomical course of the vagal and recurrent laryngeal nerves, there are many disease processes that can cause VCP. Surgery, malignancy, trauma, infection and inflammation can all result in VCP. A review of more than 800 patients showed that iatrogenic injury by mediastinal and neck surgery is the most important cause of VCP . Around 40 % of unilateral VCP and 50 % of bilateral VCP is caused by surgical injury. Bilateral VCP was more often caused by thyroid surgery, while unilateral VCP was more often caused by other surgery, like carotid endarterectomy, anterior approaches to the cervical spine, and heart or great vessel surgery. Unilateral VCP was idiopathic in almost 20 % of cases. Malignancy outside the larynx was the third most common cause of unilateral VCP, being responsible for 14 % of cases. Traumatic injury causes about 6 % of all unilateral VCPs and is most frequently intubation related. Less common causes were central nervous system disease, infection, inflammation, radiation therapy, and aortic aneurysm.
Clinically, vocal cord function can be assessed by laryngoscopy, during which a stroboscopic light can confirm the absence of movement of the affected side. Symptoms of VCP include: hoarseness, vocal fatigue, loss of vocal pitch, shortness of breath and aspiration . However, about 30–40 % of patients with unilateral VCP are asymptomatic [3, 4]. In these patients, presence of VCP is an incidental finding and the radiologist may be the first to report it. Due to the wide range of possible locations for lesions that can cause cord paralysis, it may be a first sign of extensive and severe pathology. Radiologists must therefore be able to recognise the imaging findings of VCP.
This review focuses on the anatomy and imaging evaluation of the vagal and recurrent laryngeal nerves and thereby the possible sites for pathology causing VCP. The imaging characteristics and imaging mimics of VCP are discussed and cases from daily practice illustrating various causes of VCP are presented.