Cystic Schwannoma of the Recurrent Laryngeal Nerve, a Rare Cause of Vocal Cord Paresis

Summary

We present a case of a 37-year-old woman with cystic swelling at the left lobe of the thyroid gland otherwise unrelated to the thyroid gland. Endocrinologist recommended tumour excision with left-sided hemithyroidectomy. Paresis of the left vocal cord was diagnosed preoperatively. A connection between para-glandular swelling and the left recurrent nerve was confirmed during surgery. Due to the large volume, the lesion was removed after having been debulked by puncture. In the postoperative period, the left vocal cord paresis persisted. A cystic schwannoma was verified histologically.

KEYWORDS:
cystic schwannoma, vocal cord paresis, recurrent laryngeal nerve

INTRODUCTION

Schwannoma (Neurilemmoma, Neurinoma) is a benign tumour composed of Schwann cells, which affects myelinated peripheral nerves and spinal nerve roots. It is usually a solid benign tumour with clear boundaries (6). Infrequently, even malignant forms can occur. (9) In rare cases the tumour can undergo cystic changes, then a cystic form of this tumour develops. In the ENT specialty, we often come across schwannomas in the region of the cerebellopontine angle where they develop from Schwann cells of the vestibular nerve (2, 6, 10). Schwannomas constitute 8-10% of all intracranial tumours and in the region of cerebellopontine angle it is 80 up to 90% (2). As many as 25% of all Schwannomas are located in the area of the head and neck. Another quite frequent location is the mediastinum and retroperitoneum (6, 10). The literature describes a rare occurence of solitary circumscribed neuroma of the larynx (8). Surgical exstirpation is the treatment of choice for benign Schwannomas. Due to their close connection to the nervous system, postoperative neurologic complications are not uncommon. (1, 10)

CASE

A 37-year-old female patient was first kept for under observation for one year at the Department of Endocrinology due to the swelling in the left lobe of the otherwise unchanged thyroid. The ultrasound revealed an echogenic cystic nidus measuring 28x40x20 mm. After an additional CT scan of the neck, we could specify the anatomical circumstances – the septated paraglandular cystic lesion did not come out of the thyroid gland, lymphangioma was suspected (Fig. 1).

An Ultrasound guided FNAB was not indicated for suspected lymphangioma. The planned therapeutic procedure remained unchanged.

Exstirpation via a Kocher incision was indicated. After the left sided hemithyroidectomy, paraglandularly on the left, we extracted a smooth cystic mass measuring 5x4x3cm which was attached to the recurrent laryngeal nerve and macroscopically behaved like a suspected neurinoma. Due to it volume we performed a puncture - 5ml of yellowish serous fluid was aspirated. Even so, the cystoid (structure) could not be removed without interrupting the continuity of the nerve. Because of preoperative paresis of the vocal cord on the left, we ligated the nerve and removed the entire mass. In the postoperative period, vocal cord paresis persisted.

Histopathological examination revealed a pseudocystically changed neurinoma.

DISCUSSION

Schwannoma is a benign tumour composed of Schwann cells that affects myelinated peripheral nerves and spinal nerve roots. The symptoms vary depending on the size and location of the tumour. This could be a case of paresis of the affected nerve, or a cystic swelling in which case, the paresis of the affected nerve is diagnosed only after a more detailed examination. Symptomatic progression is not an exception.

In our case, a preoperative paresis of the left vocal cord was present. Due to the preoperative findings (the mass coming directly out of the recurrent laryngeal nerve), the continuity of the nerve was impossible to preserve (10).

Generally, according to the mechanism we distinguish between direct and indirect nerve damage. The indirect mechanism is caused by an injury, an interruption or a ligation of the accompanying artery. The indirect mechanism is caused by pulling or repression caused by oedema, inflammation or hematoma in this area. The prognosis of a particular (type of) nerve paresis depends on the mechanism of its occurrence. The indirect damage can be reversible, a complete regeneration can appear within 5 months after the intervention. In case of a complete direct damage, the symptoms persist, as in our case. (1, 6, 10)

Schwannomas of the recurrent laryngeal nerve occur only rarely. In medical literature, they are globally presented as individual case reports.

Knulst et al. presented a paper on the cystic schwannoma of the recurrent laryngeal nerve. Dutch authors discuss, among other things, the importance of imaging in diagnosing cystic lesions of the neck. As a future prospect, Positron Emission Tomography scans are mentioned as a modality with possibilities to discriminate a cystic schwannoma from other common cystic lesions. (5).

Japanese authors present the case of a large (14 cm) tumor – a schwannoma of the recurrent laryngeal nerve (7). Kennedy and colleagues describe a case of a 68-year-old female with a laryngeal schwannoma of the recurrent laryngeal nerve after a traumatic injury (4). Kahraman at al describe Horner´s syndrome from gigantic Schwannoma of the cervical sympathetic chain (3).

CONCLUSION

Fine-needle aspiration biopsy (FNAB), which can reveal the origin of a neuroectodermal tumour, plays an important role in the diagnostics of the cystic swelling of the neck. In our case, G-FNAB was not indicated due to the preoperatively suspected lymphangioma. After the extirpation of the tumour of neuroectodermal origin, postoperative neurological complications have to be reckoned with. In our case it was preoperative injury to the left recurrent laryngeal nerve by the tumour and a consequently developed left vocal cord paresis. The patient is currently being treated by a phoniatrist, we do not expect reversal of the condition. In most cases schwannoma is a benign tumour the extirpation of which becomes a curative intervention. A histological examination is performed to exclude a rare malignant form of a tumor.

This work was supported by project of Ministery of Defense MO 1012.

Adresa ke korespondenci:

MUDr. Barbora Synková

ORL klinika ÚVN Praha

U Vojenské nemocnice 1200

169 02 Praha 6

e-mail: barbora.synkova@uvn.cz