Recurrent laryngeal nerve schwannoma: same setting of resection and injection laryngoplasty

Abstract

A 33-year-old woman was diagnosed with right recurrent laryngeal nerve (RLN) schwannoma. She presented with a long history of hoarseness, and only recently developed dysphagia. On physical examination, a mass was observed over the right cervical level IV. Endoscopic examination of the larynx showed that she had right unilateral vocal cord palsy. She successfully underwent transcervical resection of the tumour followed by injection laryngoplasty. This study discusses the presentation of the tumour, radiological findings, our working diagnosis and treatment options of RLN schwannoma.

Background

Schwannoma is a benign neoplasm that arises from Schwann cells.¹ It is the second most common peripheral neural sheath tumours (PNSTs), after neurofibroma.² Approximately 25%–45% of extracranial schwannoma can be found in the head and neck regions, especially in the parapharyngeal space.³ Here, it commonly originates from either the cervical sympathetic trunk or vagus nerve. A schwannoma grows from a single nerve fascicle, where it may cause displacement and impingement of the surrounding nerve fibre, thus affecting that particular nerve function.³

Case presentation

A 33-year-old woman presented with a history of hoarseness for 19 years. Her voice was gradually worsening over the years before she developed dysphagia toward solid foods, and showed symptoms of aspiration 3 months prior to her first visit to otorhinolaryngology clinic. There were no symptoms of upper airway obstructions or neck swelling. Otherwise, she had no prior medical illness and surgery. On examination, her voice was dysphonic with breathiness as the main component. There was a vague swelling over the right cervical level IV, just anterior to the sternocleidomastoid muscle, measuring 3×4 cm. The mass appeared to be mobile, firm and non-tender. There were neither any skin changes nor sinus opening. Endoscopic examination of the larynx showed right vocal palsy at the paramedian position with the right arytenoid prolapsed anteromedially and presence of phonatory gap. There was fullness over the right piriform fossa; however, no obvious mass was seen (video 1).

Video 1.

bcr-2021-245193supp001.mp4 ^{(668.9KB, mp4)}

DOI: 10.1136/bcr-2021-245193.video01

Investigations

MRI of the neck and base of the skull showed a well circumscribed mass measuring 2.5×2.7 × 5.1 cm located at the right tracheoesophageal groove. It appeared hypointense at the T1 weighted image. On the T2 weighted image, ‘target sign’ was present, characterised by heterogeneous enhancement with a hypointense centre (figure 1). The mass displaced the right thyroid lobe anteriorly while medially it obliterated the right piriform. It displaced both the common carotid artery (CCA) and internal jugular vein (IJV) laterally and lay in close proximity to the prevertebral space posteriorly with a clear fat plane between them. No biopsy was performed prior to the surgery.

Figure 1.

MRI neck T2 weighted image. A: axial view shows tumour with target sign (*) at the right tracheoesophageal groove, displacing the internal jugular vein (i) and common carotid artery (c) laterally. B: coronal view shows the tumour (*) with stalk supero-medially causing compression of the right piriform fossa (p).

Differential diagnosis

Common causes of dysphonia are laryngitis followed by functional dysphonia, laryngopharyngeal reflux, benign and malignant neoplasm of the larynx and neurological causes such as vocal cord palsy.⁴ Examination of the larynx by using laryngoscopy is an important procedure to make a diagnosis, which in this case was right vocal cord palsy. With the presence of a neck mass over the ipsilateral side as the affected vocal cord, it was believed that the mass had caused impingement of vagus nerve or RLN. RLN is a branch of the vagus nerve that supplies the phonatory muscle of the larynx. Any lesion that affects either the vagus nerve or RLN may cause unilateral vocal cord palsy and, thus, hoarseness.

A chronic lateral neck mass can be caused by congenital mass such as branchial cleft cyst, benign neoplasm such as carotid body tumour and PNSTs. Malignancy causes such as metastatic head and neck squamous cell carcinoma, lymphoma and thyroid malignancy are possible, but they usually progress in months rather than years as in this case. Infection or inflammatory causes such as reactive lymphadenopathy from mycobacterium infection may also progress in the same manner but they usually have other symptoms such as pain and fever.⁵

From the MRI images, the presence of a ‘target sign’ on the T2 weighted MRI was suggestive of PNSTs rather than metastatic carcinoma⁶ MRI features that suggestive of metastatic carcinoma such as round lymph node, irregular border, heterogeneous signal intensity on T2 weighted images and central necrosis are absence from this patient.⁷ Given that the tumour was originating from the right tracheoesophageal groove, we suspected it originated from the right RLN. Vagal schwannoma may present with similar symptoms but the MRI findings did not correlate with this condition. In enlarged vagal schwannoma, the tumour has a tendency to displace IJV and CCA medially but not in this case, as both of the structures were displaced laterally.⁸ Schwannoma of the cervical sympathetic chain may have similar findings on MRI, that is, it may displace both the CCA and IJV laterally but the tumour is likely to present with Horner’s syndrome rather than unilateral vocal cord palsy.⁹ A carotid body tumour may also present with anterior neck mass and multiple cranial nerve palsy including RLN but it is located more superior at the carotid bifurcation and will display the classic ‘salt and pepper’ sign on MRI. The low signal flow void within the carotid body tumour gives the appearance of ‘pepper’, while high signal foci of haemorrhage correlate with the appearance of ‘salt’.^{10 11}

Treatment

We proceeded with resection of the tumour via a transcervical approach followed by transoral injection laryngoplasty using calcium hydroxyapatite. Intraoperatively, a well lobulated mass was identified at the right tracheoesophageal groove, deep to the right thyroid lobe (figure 2). The tumour appeared to have a stalk supero-medially, abutting the right piriform fossa. The tumour was excised as a whole and the surgery was followed by transoral injection laryngoplasty. About 1.2 cc calcium hydroxyapatite was injected at the right paraglottic space until adequate medialisation of the right vocal cord was achieved. Vocal cord medialisation was performed to close the phonatory gap, thus improve vocalisation and reduce the risk of aspiration. Post-operatively, the patient underwent voice and swallowing rehabilitation.

Figure 2.

A: intraoperative view of the neck after subplatysmal flap elevation. the tumour (*) is seen after sternocleidomastoid muscle (sc) and strep muscle (st) retraction. superior (s), anterior (a), inferior (i), posterior (p). B: resected tumour.

Outcome and follow-up

Histopathological examination of the excised tumour revealed spindle cell proliferation arranged in alternating cellular Antoni A and hypocellular Antoni B areas, suggestive of schwannoma. The patient was discharged 2 days after surgery. During follow-up in a month, she had less hoarseness, no aspiration symptoms and no dysphagia. Endoscopic examination of the larynx showed an immobile right vocal cord in the median position while her left vocal cord was mobile with no phonatory gap. The fullness over the right piriform fossa was no longer present.

Discussion

PNSTs are rare tumours originating from Schwann cell differentiation. About 90% of PNSTs are benign and comprise neurofibroma and schwannoma. Malignant peripheral neural sheath tumour is uncommon but most are high grade tumours.¹² A schwannoma grows within the epineurium from a single nerve fibre, splaying the rest of the nerve fibre.³ In comparison, a neurofibroma arises for the perineurium and consists of additional cells such as neuronal axons, fibroblasts, mast cells, macrophages, perineural cells and extracellular matrix materials.¹³ Both tumours can arise from any part of the body and are virtually indistinguishable prior to surgery. Vagal schwannoma is a slow growing tumour that is present with a painless neck mass. Only a small number of patients develop hoarseness due to unilateral vocal cord palsy. Syncope and paroxysmal cough during palpation caused by vagal stimulation are rare symptoms.¹⁴

MRI is the imaging of choice to evaluate and plan for surgery for PNSTs. Both schwannoma and solitary neurofibroma share similar features on MRI such as being fusiform in shape, less than 5 cm in size and with intermediate signal intensity on T1 weighted images and high signal intensity on T2 weighted images. Moreover, both tumours also demonstrate split-fat sign, fascicular sign or target sign, which was present in this case. The target sign is a biphasic pattern of the tumour on MRI T2 weighted image characterised by peripheral high intensity and central low intensity and vice versa for T1 weighted image. It has 100% sensitivity and 59% specificity for schwannoma but may also be present on neurofibroma.¹⁵ All the similarities make it very difficult to confidently distinguish both tumours on MRI; the only way to diagnose them is from histopathology examination.⁶

Despite playing a key role in most neck mass workup, fine-needle aspiration provides less valuable information for PNSTs.⁹ It is difficult to diagnose PNSTs from cytological smears due to frequent poor cellularity or lack of cells. Often, the cytological finding can easily be confused with other benign or soft-tissue tumours, making the tool unreliable for PNSTs.¹⁶ For this patient, information from MRI was sufficient enough for us to diagnose a PNSTs and proceed with surgery.

Given that the majority of vagal schwannoma presents with asymptomatic neck mass, observation with serial imaging is an option depending on the size, location and overall health condition of the patient. Surgery is usually indicated in symptomatic patients. This occurs when the tumour is enlarged and causes nerve dysfunction or compression of adjacent structures.³ The surgical approaches comprise intracapsular enucleation or en bloc resection of the tumour. Intracapsular enucleation has the potential of preserving the vagus nerve fibre, thus maintaining vocal cord function but at the expense of having the risk of recurrence. Despite its promising nature, a study comparing both techniques showed only 20% of patients who underwent intracapsular enucleation retained their vocal cord function while having 33% risk of recurrence. Undoubtedly, en block resection of vagus schwannoma is superior in terms of local clearance while having comparative results on post-operative voice quality.¹⁷

Few case series have proposed using intermittent intraoperative nerve monitoring during intracapsular enucleation of vagus schwannoma.³ This technique allows surgeons to identify the location of the nerve fibre running over the tumour surface, thus avoiding injury to the nerve fibre. Nevertheless, this technique is not useful in this case given that the patient already had unilateral vocal paralysis from the tumour compression.

Injection laryngoplasty is a treatment for unilateral vocal cord palsy. During this procedure, a filler material is injected into the right paraglottic space by using a needle to medialise the vocal cord. This is to reduce glottic insufficiency, improve phonation and prevent aspiration. It was concurrently performed during this surgery because the right RLN function was already affected before surgery and was expected not to recover after the surgery. The procedure needs to be repeated periodically, every few months, and can be done in an office setting under local anaesthesia.¹⁸

Patient’s perspective.

I waited for a very long time before decided to seek medical treatment for my voice. I felt that my voice had changed but I was being dismissive and took it for granted. It was until I developed difficulty in swallowing that I realised that something needs to be done.

To my surprise, the doctor discovered that one of my voice boxes was not functioning, and there was a swelling compressing my throat. I felt very disappointed and helpless, and some regret because I did not seek medical assistance earlier and waited for years. However, the doctor was very supportive, and he reassured me that the mass did not look like a cancer. He informed me that after treatment, with some voice and swallowing rehabilitation, my swallowing and voice may improve.

I agreed for the surgery, which went well. After the surgery, I felt mild discomfort on my neck and in my throat. Swallowing was slightly painful and difficult. I was instructed to rest my voice for a few days. The doctor showed me the tumour that he removed, it looked like a whitish flesh. After few days, I was allowed to vocalise slowly. I had to stain more to speak while voice quality was still the same. I was pleased that the surgery went well but at the same time quite disappointed with the quality of my voice. The doctor reassured me that the voice quality will improve over the next few weeks.

By the time of my next appointment after a month, my voice had much improved and I did not have to strain as much as before to speak. My voice only got worse if I overuse my voice during the day. With the help from my speech and language therapist, I learnt new swallowing techniques. With this technique, I had less coughing during swallowing. Although I realise that I may need repeated injections to my voice box in the future, I am quite satisfied with my current condition.

Learning points.

• Any prolonged hoarseness needs to be referred to otorhinolaryngologist for further investigation to rule out organic causes such as malignancy and vocal cord palsy.

• Despite its indolent nature, a schwannoma may lead to functional loss due to neve impingement and surrounding structure compression.

• Despite advanced imaging techniques, especially MRI, there remains no clear criteria to reliably distinguish a schwannoma from a neurofibroma. Histopathological examination is still the gold standard to diagnose these conditions.

• Observation with serial imaging is an option for vagal schwannoma depending on the size, location, patient’s symptoms and patient’s general health.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s)