Abstract
We present here the first case report of a mucoepidermoid carcinoma of the parotid infiltrating the chorda tympani nerve and also discuss why an initial diagnosis of Bell palsy may be misleading.
1
Introduction
Malignant tumors infiltrating the facial nerve present clinically with facial palsy and require wide surgical excision before facial nerve grafting. Postoperative radiochemotherapy is frequently administered depending on the histology and tumor staging. Although perineural spread is a hallmark of an adenoid cystic carcinoma, the more frequent mucoepidermoid carcinoma is also known to progress along the nerve fibers, and intraoperative frozen sections are required to define clear margins before placing any nerve graft . We present a case report of a mucoepidermoid carcinoma of the parotid infiltrating the facial nerve and extending into the chorda tympani and discuss the diagnostic and therapeutic challenges.
2
Case report
A 63-year-old man presented with a mild left-sided facial nerve dysfunction. Clinical examination did not reveal any further pathology, and the patient was diagnosed as having Bell’s palsy and treated with steroids. His facial function recovered fully, but over a period of 2 months, recurrent spells of facial palsies progressed to a complete paralysis. His family practitioner referred the patient to a neurologist, and 2 magnetic resonance imaging (MRI) scans and laboratory tests did not reveal any pathology. Electroneurography showed marked denervation. He was reassured to be patient and to expect partial recovery. Because no improvement was observed after 9 months, the patient was referred to our center for facial reanimation. Although the first brain MRI did not reveal any pathology, we noticed on a coronal section on the second (MRI scan) a parotid tumor. Further workup ( Fig. 1 ) including fine-needle aspiration cytology verified a mucoepidermoid carcinoma of the left parotid gland. The patient was unaware of any taste loss but presented with a total peripheral facial palsy. The patient was counseled for partial mastoidectomy, total parotidectomy, and selective neck dissection with auricular and sural facial nerve grafting. Intraoperatively, the proximal facial nerve was infiltrated on repeated frozen sections up to the outer genu at its turn from the mastoid to the tympanic segment ( Fig. 2 ), although the fallopian canal was intact and the nerve itself did not appear conspicuous under the operating microscope. Because middle ear surgery had not been discussed preoperatively, the tumor was totally resected except an uncertain margin within the tympanic segment. A hypoglossal-peripheral facial nerve jump graft anastomosis was performed, and a gold weight lid loading was accomplished.
On the day after surgery, the patient was informed upon the unexpected proximal extension, and 10 days later, an endaural middle ear exploration was performed, the incus was temporarily removed, and the tympanic segment was resected without further evidence of carcinoma infiltration. The chorda was cut underneath the anterior malleal ligament, and the bone was drilled proximally toward the previous mastoid division. The chorda was completely resected and sent for final histology. After incus interposition for hearing restoration, the patient was sent for radiotherapy because of the advanced stage of the disease (T4aN0M0).
Final histology revealed high-grade mucoepidermoid carcinoma of the salivary gland, which was multifocal and involved the entire gland. Two of the 13 peri- and intraparotid lymph nodes were positive along with infiltration of major peripheral nerves and accompanying soft tissue and skeletal muscles. The tympanic segment was free of tumor, but the chorda showed microinfiltration measuring 1.6 mm of mucoepidermoid carcinoma with an otherwise intact mucosa ( Fig. 3 ). It also showed epithelial calcification suggestive of inactive and low-grade chronic inflammation.
