- Pictorial Review
- Open Access
Vocal cord paralysis: anatomy, imaging and pathology
© The Author(s) 2014
- Received: 16 July 2014
- Accepted: 30 September 2014
- Published: 15 October 2014
Vocal cord paralysis (VCP) can be caused by any process that interferes with the normal function of the vagal nerves or recurrent laryngeal nerves. It may be a first sign of extensive and severe pathology. Radiologists must therefore be able to recognise the imaging findings of VCP and know the course of the vagal and recurrent laryngeal nerves. This review focuses on the anatomy and imaging evaluation of these 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 causes of VCP are presented.
• Vocal cord paralysis may be the first presentation of severe pathology.
• Radiologists must be aware of imaging characteristics and mimics of vocal cord paralysis.
• Lesions along the vagal nerves and recurrent laryngeal nerves can cause vocal cord paralysis.
- Vocal cord paralysis
- Vocal cord anatomy
- Vagal nerves
- Laryngeal nerves
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.
Anatomy of the vocal cords and their innervation by the vagal nerves and recurrent laryngeal nerves [5, 6]
Brainstem and skull base
Bilateral VCP is indicative of a central cause in the medulla oblongata . Acute onset of symptoms also points toward a central cause. The area of the medullary nuclei of the vagal nerve can best be evaluated with magnetic resonance imaging (MRI) [9, 10], using T2-weighted imaging, diffusion-weighted imaging (DWI) and T1-unenhanced and gadolinium-enhanced imaging. Possible pathology in the medulla oblongata comprises demyelinating diseases, infarction and intra-axial tumours [1, 7, 11, 12]. The cisternal part is best visualised by high-resolution heavily T2-weighted sequences and T1-weighted imaging with gadolinium [13, 14]. At this location, the vagal nerve can be affected by external compression by extra-axial masses, vascular structures, or by pathology that affects the nerve itself like schwannoma, paraganglioma or neuritis [1, 7, 11, 12]. If multiple cranial nerves are involved, the jugular foramen should be scrutinised. Pathology in and around the jugular foramen is best depicted by an MRI of the posterior fossa comprising T2-weighted imaging, DWI and T1-unenhanced and gadolinium-enhanced imaging [9, 13, 14].
Extracranial vagal nerves and recurrent laryngeal nerves
To depict pathology in the course of the extracranial vagal nerves and the recurrent laryngeal nerves, we prefer contrast-enhanced computed tomography (CT) from the midbrain to the aortic arch including the AP window (Fig. 3a) . With multi-slice detector CT scanners the whole volume can be acquired with isotropic voxels with a slice thickness of 0.625 mm. The scan duration is only several seconds, which allows for a minimum of image quality degradation by breathing-induced and swallowing-induced motion artefacts. The CT should be acquired during quiet breathing, in order to bring the vocal cords to an abducted position (Fig. 1a). The isotropic voxels make it possible to make reconstructions in any plane of choice (preferred slice thickness of 2–3 mm). Axial reconstructions should always be obtained parallel to the true vocal cords for optimal diagnostic accuracy. Frequently occurring pathologies that cause extracranial vagal or recurrent laryngeal nerve palsy are lung cancer with mediastinal lymph node metastases and squamous cell carcinoma of the neck with or without local lymph node metastases [1, 7]. However, other pathologies like infectious processes, benign masses or malignancies of other structures in the neck and upper mediastinum can all cause VCP [1, 7, 11, 12].
VCP can be caused by any offending lesion in the course of the vagal and recurrent laryngeal nerves, between the medulla oblongata and the aortic arch. Since VCP may be the first presentation of pathology the radiologist has to be aware of (1) the imaging characteristics and mimics of VCP, (2) the expected course of the vagal nerves and recurrent laryngeal nerves, and (3) the different types of pathology that can occur along their course.
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