INTRODUCTION: Unilateral vocal cord palsy is most commonly idiopathic or secondary to malignant or iatrogenic causes. We present a rare case of cord palsy due to a benign mediastinal parathyroid cyst.
CASE PRESENTATION: A 51-year-old previously well Chinese man presented with hoarseness of voice for two months. He was otherwise asymptomatic and serum calcium levels were normal. Chest radiography and CT scanning showed a well circumscribed cystic lesion measuring 5.8 x 4.4 x 9.5cm at the right posterior aspect of the trachea. The lesion displaced the trachea anteriorly, and its left lateral border abutted the aortic arch in the area of the left recurrent laryngeal nerve. Bronchoscopy confirmed unilateral left vocal cord palsy. Surgical exploration via a left thoracotomy revealed a cystic mass in the posterior mediastinum filled with clear fluid and extendeing from the thoracic outlet to the inferior edge of the aortic arch. The lesion was completely resected. Histological examination demonstrated a benign cyst strongly expressing parathormone and neuroendocrine antibodies for CD56 and chromogranin A, consistent with a diagnosis of a parathyroid cyst. The patient made a satisfactory post-operative recovery and his voice returned to normal.
DISCUSSIONS: Parathyroid cysts are classified as cervical or mediastinal depending on their location. A parathyroid cyst was first described in the mediastinum by de Quervain in 1925. Since then, just over 100 cases of mediastinal parathyroid cysts have been reported in the literature. Mediastinal parathyroid cysts are typically benign, thin-walled, unilocular lesions filled with clear or brownish fluid. They can range from 0.5cm to 12cm in diameter and are usually solitary. They tend to occur in the anterosuperior or middle mediastinum. Posterior mediastinal lesions such as in our patient are rare. Mediastinal parathyroid cysts have been reported in adults from 24 to 83 years of age with no peak incidence related to age. The distribution between sexes is equal. Parathyroid cysts in the mediastinum are often asymptomatic. However, around 40% are functional, producing varying levels of parathyroid hormone (PTH). Patients may therefore present with symptoms of hyperparathyroidism and even acute hypercalcemic crises. Symptoms can also result from a large cyst compressing on mediastinal structures. Dyspnea due to tracheal compression and dysphagia due to esophageal compression have been reported. Compression on the recurrent laryngeal nerve as it crosses the aortic arch may result in left vocal cord palsy. Since 1925, there have only been 10 cases to our knowledge of patients with a mediastinal parathyroid cyst presenting with unilateral vocal cord palsy. Conversely, malignant, iatrogenic and idiopathic etiologies account for over 90% of cases of unilateral cord palsy. A mediastinal parathyroid cyst represents one of the very rare benign causes. Assuming that a mediastinal lesion causing cord palsy is incurable may preclude some patients from potentially curative surgery. Pre-operative diagnosis is confirmed by analysis of the fluid from the cyst that shows increased PTH, although in many cases diagnosis is made only on histological analysis of the resected specimen. Although CT, MRI and ultrasonography may aid pre-operative planning, parathyroid scintigraphy has thus far not been proven to be useful. The treatment of choice is complete resection via a transcervical, open thoracotomy or video-assisted thoracic surgery (VATS) approach. Regardless of approach, no deaths and very few complications related to surgery have been reported. No recurrences have been reported. Fine-needle aspiration may have a palliative role in patients not fit for surgery.
CONCLUSION: Patients presenting with voice hoarseness and a mediastinal lesion on imaging may have a surgically curable mediastinal parathyroid cyst rather than an untreatable malignancy. Early surgical referral should be considered in selected cases.
DISCLOSURE: Alva Sit, None.