Imaging the causes of vocal cord paralysis Poster No.:

C-1526

Congress:

ECR 2011

Type:

Educational Exhibit

Authors:

A. Clayton, H. Khirwadkar, M. Hourihan; Cardiff/UK

Keywords:

Head and neck, Ear / Nose / Throat, Thorax

DOI:

10.1594/ecr2011/C-1526

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Learning objectives • Review of the normal imaging anatomy of the medulla, larynx and the vagus nerve with its branches. • The causes of vocal cord paralysis will be discussed.

Background Vocal cord paralysis (VCP) has a variable aetiology and can be caused by pathology in the brainstem or anywhere along the course of the nerves supplying the vocal cords. When vocal cord paralysis occurs, the true vocal cords, also commonly referred to as vocal folds, do not open or close properly. This is usually due to a malfunction of the internal laryngeal muscles and is a sign of an underlying disorder and not a disease in itself. VCP is common and symptoms range from mild to life threatening. Paralysis can be caused by damage to: the vagus nerve(s) including its nuclei within the medulla oblongata, the recurrent laryngeal nerve, the external superior laryngeal branches, or from pathology of the larynx. The many causes include iatrogenic, tumour infiltration/compression, trauma, vascular, myopathy, degeneration, neurological insult, inflammation and infection. Some cases are idiopathic, with no cause found.

Imaging findings OR Procedure details Normal Anatomy The recurrent laryngeal (RLN) and superior laryngeal nerves (SLN) originate in the nucleus ambiguus (NA), the motor nucleus of the vagus. Within the medulla, the NA is approximately 2 cm long and lies within the reticular formation. The middle portion projects fibres to form the vagus nerve which leaves the upper medulla, travelling in the 1

posterolateral groove to exit the skull through the jugular foramen.

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Fig.: Parallel axial MR and diagrammatic images of the nucleus ambiguus within the medulla. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM Both vagus (latin for wandering) nerves descend along the posterolateral aspect of the internal carotid artery and in front of the cervical sympathetic chain. Distally the nerves have a different course on each side. Approximately 36mm below the jugular foramina, the superior laryngeal nerve branches from the vagus, travelling with the superior thyroid artery and entering the larynx through the thyrohyoid membrane to 2

innervate the cricothyroid muscles.

On the right, the RLN branches off the vagus nerve, looping under the subclavian artery, and ascends superiomedially towards the tracheo-oesophageal groove. It runs near the inferior thyroid artery to enter the larynx posterior to the cricothyroid joint.

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Fig.: Diagramatic represenatation of the course of the vagus and laryngeal nerves.

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References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM The left RLN branches at the aortic arch, runs posteriorly, ascending in the aortopulmonary window, and tracking superiorly in the tracheo-oesophageal groove to enter the larynx posterior to the cricothyroid joint.

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The larynx is a complex musculo-cartilaginous organ extending from C3 to C6 in the midline. Its skeleton consists of the hyoid bone and the cartilaginous structures of the thyroid, cricoid, epiglottis and paired arytenoids. The vocal cords stretch anteriorly from 2&4

the immobile mid-portion of the thyroid cartilage to the mobile anterior arytenoids.

Fig.: Diagrammatic representation of the larynx. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM The RLN provides the nerve supply of the thyroarytenoid, posterior cricoarytenoid, lateral cricoarytenoid and interarytenoid muscles of the larynx. The extrinsic cricothyroid muscle is supplied by the external branch of the superior laryngeal nerve.

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Pathology

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Vocal cord paralysis (immobility) and vocal cord paresis (hypomobility) implies laryngeal muscle malfunction. This may be from unilateral or bilateral nerve injury. If both sides are affected the cause might be found in the brainstem. Complete RLN damage gives a paramedian position of the vocal cord as the cricothyroid muscles that function as 5

adductors are spared. A high lesion in the medulla or neck that involves both SLN and RLN will give a slightly more lateral position of the vocal cord, so patients are more likely to have swallowing problems and are at a higher risk of aspiration.

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Normal voice production is dependent on proper glottal closure resulting from bilateral adduction of the vocal cords. This adduction of vocal cords combined with subglottic air pressure results in vibration of the vocal cords causing phonation.

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VCP often presents with hoarse voice. In an observational study of 293 patients aged 65 and over presenting with hoarse voice, the cause in 29% of cases was vocal cord paralysis, 16% of cases had laryngeal or hypopharyngeal cancer, and 49% 8

muscle tension/functional dysphonia. Other symptoms of vocal cord paralysis include dysphonia, loss of the upper register of the voice, breathiness, throat pain, choking 3

episodes or decreased vocal stamina.

The pathophysiology of VCP is complex. In a review of 7 published studies including 1308 patients with vocal cord paralysis, surgical trauma was implicated in 22% of cases, malignancies (primarily thyroid and lung) in 22%, infection/inflammatory causes in 36%, 9

neurological in 4% and the remaining 16% were idiopathic.

In the absence of previous neck or mediastinal surgery, laryngeal tumour or trauma, investigations should image locations from the vagal nuclei in the brainstem down to the aortic arch. VCP is considered a common disorder

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and as such, radiology has a

significant role in identifying these other causes of vocal cord paralysis.

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Although the RLN, (which is more frequently injured than the SLN), may be damaged anywhere along its course from the brainstem to the larynx, the left side is more frequently 11

affected because of its longer course (by 28%) into the mediastinum.

Peripheral causes

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of vocal fold paralysis are more common than central causes. The Medulla

Central nervous system disorders associated with VCP include cerebrovascular disease, (brainstem stroke is the commonest cause), multiple sclerosis, multiple system atrophy,

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Parkinson's disease, progressive supranuclear palsy, Arnold Chiari Malformation and progressive bulbar palsy. Neurological conditions, such as multiple sclerosis or Parkinson's disease are more likely to cause vocal cord weakness than complete 13

paralysis.

Fig.: T2 MRI with a MS plaque in the left medulla causing VCP. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM

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Small lesions of the NA may produce isolated laryngeal motor losses, more often bilateral than unilateral. Tumours of the Larynx Laryngeal tumours cause mechanical interference with vocal cord function. The larynx accounts for approximately 25% of head and neck malignancies, with 90% being squamous cell carcinomas associated with cigarette smoking and excessive 12

consumption of alcohol.

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Fig.: Axial CT showing a right vocal cord squamous cell carcinoma presenting as VCP. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM

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Patients with glottic cancer (65-70% of laryngeal cancers) often present with hoarseness. Supraglottic tumours (30%) have space to grow without causing symptoms and so are commonly diagnosed at a later stage, when presenting with a neck lump (lymph node metastasis), sore throat, referred otalgia or dysphagia. Subglottic cancer is rare and often 14

presents at a late stage with hoarseness from tumour invasion of the vocal cords.

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Fig.: Axial CT showing a large laryngeal carcinoma causing a VCP. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM

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Damage to the Recurrent Laryngeal Nerve Iatrogenic Trauma Surgical trauma, mainly thyroidectomy, is the most common cause of VCP in hospitalised 15

patients. However surgical intervention involving the anterior cervical spine, cardiac, pulmonary, aortic arch, carotid artery and other head and neck surgery can also injure the RLN.

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A study of 193 patients with VCP found 35.8% were related to surgery or intubation, 17

with thyroid and thoracic/cardiac procedures having nearly equal causation. Iatrogenic injury can occur from intubation, crush, division, traction, ligature placement and thermal 3

injury. Figures for injury to the RLN from thyroid surgery vary between 0.3% and 13.2%, from anterior cervical spine surgery between 2% and 21.6% and from thoracic aortic aneurysm surgery between 12 and 32% of patients.

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Non Iatrogenic Trauma Injuries to the neck caused by 'sport', automobile accidents and penetrating neck injuries can cause vocal cord palsy. Tumour Around 22% of cases of vocal cord paralysis are secondary to a neoplastic cause. Lung cancer infiltrating the left upper mediastinum where the RLN passes around the aortic arch causes left vocal cord paralysis. Less often, tumour of the right superior chest wall, where the nerve courses around the subclavian, is implicated.

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Fig.: Carcinoma of the lung involving the left RLN as it loops around the aortic arch. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM 19

Thyroid, oesophageal, lymph node tumours and Pancoast tumours can injure the RLN.

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Fig.: Axial CT image demonstrating para-aortic lymphadenopathy compressing the left RLN. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM Compression secondary to thyroid disease such as a large thyroid goitre is uncommon. Patients with a unilateral vocal cord paralysis will have thyroid disease in 4%, though only 0.7% with benign thyroid disease will have a RLN paralysis.

20-22

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Fig.: Axial CT of a thyroid goitre causing VCP. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM

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Idiopathic Idiopathic VCP, which accounts for up to 20% of cases, is poorly understood. A viral cause is suspected as many patients describe upper respiratory tract infection symptoms 3

prior to their vocal cord problems. The left vocal cord is commonly involved in these patients. Although idiopathic vocal cord paralysis is quite common, investigations should not be terminated at too early a stage as a recent study found that 34% of cases labelled idiopathic after clinical examination only, were found after thorough investigation to be 6

reduced to only 8% of cases where no cause could be identified. Another series of 193 patients found that nearly half of the 35 patients with 'idiopathic vocal cord paralysis' presented with or were subsequently diagnosed as having neurological conditions.

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Infection Infectious diseases such as Lymes disease, tertiary syphilis, Epstein-Barr virus and herpes have also been reported to cause viral neuritis and subsequent RLN 23-26

paralysis.

Tuberculosis can also cause RLN paralysis due to effects of apical scarring of the mediastinum or enlargement of hilar nodes. Vascular

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Fig.: Axial and Coronal CT image of an aneurysmal aortic arch compressing the left RLN and presenting as VCP. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM On the left side, vascular causes of RLN injury include carotid artery dissection, thoracic aortic aneurysm or dissection, and cardiomegaly (particularly from right atrial enlargement from mitral stenosis). Right subclavian artery aneurysms have also been implicated as potential causes.

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A study of 168 cases of thoracic artery aneurysms found

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an associated VCP rate of 5%.

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Fig.: CT Angiogram of a carotid pseudoaneurysm which caused VCP by compresssion of the vagus nerve within the carotid sheath. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM Case Study on page

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A 78 year old male presented with shortness of breath, anorexia, general malaise, a productive cough and drenching night sweats. On examination a splinter haemorrhage and a soft systolic murmur were observed along with elevated inflammatory markers. A transthoracic echocardiogram was performed, on which, there was a suspicion of small vegetation on the aortic valve. Subsequently the patient became unable to cough and was noticed to have a hoarse voice. ENT review found a left vocal cord palsy. A CT was arranged and this showed a 4.6cm saccular aneurysm arising from the arch of the aorta just distal to the origin of the left subclavian artery. In view of the history this was diagnosed as a mycotic aneurysm and was the cause of the vocal cord paralysis. This was treated with an endovascular stent with subsequent improvement of his vocal symptoms. Degenerative Rarely it has been reported that severe spondylophytes can compress the RLN and cause 27

vocal cord paralysis.

Fig.: Soft tissue and bony windowing axial CT images of osteophytes compressing the right RLN. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM Neurological disorders The neurological disorders reported to be associated with VCP are best divided into central nervous system disorders (cerebrovascular disease, multiple sclerosis, multiple system atrophy, Parkinson's disease, progressive supranuclear palsy and Arnold Chiari malformation) and peripheral nervous system disorders, eg Wallenburg syndrome,

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myasthenia gravis, Guillain-Barré syndrome, postpolio syndrome, Charcot-Marie-Tooth disease and chronic motor axonal neuropathy) progressive bulbar palsy.

17, 28-34

Cerebrovascular accident may injure the RLN neurones, (a 2005 study finding 9% of the 69 cases being cause by stroke)

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although this type of injury would usually involve 35-37

damage to other neurones. Diabetic neuropathy of the RLN can occur rarely.

Schwannomas arising from the lower cranial nerves are rare and the majority are located in the jugular foramina. Figure 14 demonstrates an MRI of a schwannoma of the jugular foramen that presented as VCP.

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Fig.: Contrasted Coronal MRI image of a right jugular schwannoma compressing the vagal nerve and giving rise to VCP. References: A. Clayton; Radiology, University Hospital of Wales, Cardiff, UNITED KINGDOM Sarcoidosis Sarcoidosis, a multisystem, granulomatous disease affecting the upper tract is uncommon, and vocal cord involvement is rare, but is described in 8 UK case reports.

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In addition to compressive lymphadenopathy of one or both of the RLN, sarcoidosis can 38

result in neuritis affecting the cranial nerves.

Other miscellaneous causes include haemolytic anaemia, subclavian vein thrombosis, 7

syphilis, collagen disorders, lead and arsenic poisoning. Images for this section:

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Fig. 1: Diagramatic represenatation of the course of the vagus and laryngeal nerves.

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Fig. 2: CT Angiogram of a carotid pseudoaneurysm which caused VCP by compresssion of the vagus nerve within the carotid sheath.

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Fig. 3: Axial CT image of an aneurysmal aortic arch that presented as a VCP.

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Fig. 4: Coronal CT image of an aneurysmal aortic arch presenting as VCP.

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Conclusion As illustrated, VCP is complex. With the knowledge of the anatomy of the nerve supply to the larynx, the origin of the nerves within the brainstem, their control by the cerebral cortex and awareness of the various pathologies that may result in vocal cord paralysis, it is possible to investigate and identify causes for vocal cord paralysis by performing the appropriate imaging. Contrast enhanced CT is the first line investigation for VCP. It is a readily available modality which can rapidly image the course of the vagus from the vagal nuclei in the brainstem, down to the aortic arch. Multiplanar reformatted contrast enhanced CT images with bone and soft tissue windowing provide an ideal imaging technique for the exclusion of the many causes of VCP. The majority of patients with positive radiology will have a 39

malignant cause.

MRI has a role to play when imaging the central nervous system.

The reporting radiologist may be the first person to raise the possibility of VCP and inform the unsuspecting clinician.

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