Primary facial nerve paraganglioma: report and review of the literature

Background

Paragangliomas (PGLs) are an important differential to include when dealing with head and neck soft tissue tumours. Whether arising from the facial nerve (FN) itself or nearby structures, they commonly present as progressive FN paralysis and can easily be mistaken for other, non-neoplastic conditions. Treatment of these tumours almost always consists of complete surgical excision. Delays in proper diagnosis and treatment may lead to permanent FN paralysis, emphasising the importance of this rare disease.

Case presentation

A 60-year-old Caucasian man presented with a 4-month history of progressive left-sided facial paresis that began as mild facial twitching. Steroid treatment at the time for presumptive Bell’s palsy produced no improvement and his symptoms continued to worsen. Examination revealed House-Brackmann (HB) VI/VI left facial palsy. He could no longer close his left eyelid and had to tape it shut at night. He had recently noticed increased dryness of his eyes in the morning. No vision changes, voice irregularity or loss of sensation were noted. Otoscopic examination was within normal limits. He was a non-smoker and did not drink alcohol. No relevant prior medical history was noted.

Investigations

Prior to referral to otolaryngology, the patient’s primary care physician had already begun investigation into his condition. In March, 4 months prior to his referral visit, the patient began experiencing mild left facial twitching and paralysis. Suspecting potential viral aetiology, treatment was initially attempted with oral glucocorticoids. By June, his condition progressed and he could no longer completely close his left eyelid. MRI of the head with and without contrast was performed. This revealed a small lobulated, enhancing mass lesion along the inferior portion of the descending mastoid segment of the left FN and left stylomastoid foramen.

At referral visit, these findings were found to be suspicious for an FN schwannoma. Audiogram performed at this time revealed essentially normal hearing from 250 Hz to 8000 Hz on the patient’s right ear. However, on the left ear, the patient was found to have a sloping mild-to-moderate sensory neural hearing loss at 2000–8000 Hz. Hearing between 250 Hz and 2000 Hz was normal. Speech reception threshold and Word Recognition Scores were within normal limits bilaterally. Dedicated MRI of the head with and without intravenous contrast revealed a lobulated, expansile lesion involving the distal mastoid segment of the left FN and left stylomastoid foramen with mild extension to the surrounding mastoid air cells (figure 1). With the differential diagnosis, then being FN schwannoma versus haemangioma, CT scan of the temporal bone with and without contrast was performed. This revealed a 19 mm×9 mm×9 mm soft tissue mass in the mastoid segment of the left FN as well as a focus of ‘honeycomb bone’ at the mass’ posterior aspect (figure 2). With this new evidence, the differential shifted to include either a haemangioma or possibly a skip lesion from some other malignant process. Nerve conduction studies and Electromyography (EMG) testing were instead performed on both FNs. The conduction study, performed via bilateral nasalis muscles, revealed compound muscle action potentials (CMAPs) of normal amplitude and frequency on the right. No CMAPs could be obtained from the left FN. Needle electrode examination revealed denervation of both the left frontal and orbicularis oculi muscles. No voluntary activity was identified. These findings were consistent with severe damage to the left FN and provided the need for urgent intervention to salvage nerve function.

Treatment

Following the nerve study results, a surgical team lead by an experienced neuro-otological surgeon performed a mastoidectomy with transmastoid FN decompression and nerve biopsy. During the procedure, the tympanic portion of the FN was found to be severely edematous and abnormally enlarged. Tracing the nerve inferiorly, a 2 cm mass was identified arising from the FN near the mastoid tip. Surrounded in a fibrous capsule, the mass’ location and size were consistent with previous CT scan/MRI findings. During excision, the mass was revealed to be arising from nerve itself. This was revealed when the epineurium was identified surrounding the mass as opposed to being simply adjacent to it. The later organisation being what would be expected with other such neoplasms such as haemangioma.

Biopsies were initially taken from the epineurium and sent for frozen. Results returned as non-diagnostic. The facial nerve was therefore traced back to the stylomastoid foramen and further samples were taken, for total of 25, and sent for permanent. A diagnosis of primary FN PGL was confirmed by histology. The classic nesting pattern of chief cells with abundant granular cytoplasm and evenly dispersed nuclear chromatin was consistent with neuroendocrine differentiation. The tumour displayed a prominent fibrovascular stroma between the nests (figure 3). Neuroendocrine origin was confirmed by diffuse positivity with synaptophysin (figure 4). The accompanying sustentacular cells at the periphery of the nests were highlighted with S100 (figure 5).

Following recovery, treatment options were discussed with the patient and his family. These included observation, radiation and/or complete surgical excision of the mass and involved nerve with subsequent nerve grafting. The risks and benefits of each option were thoroughly explained for each option as well as for the option of not receiving treatment at all. Emphasis was made that excision and grafting would require at least 1 year of postoperative care and could potentially return his nerve function to an HB III/VI, at best. The patient was elected for excision and grafting.

With the goal to aid in surgical tumour removal, 3 days prior to surgery, an interventional radiology team successfully immobilised the tumour feeder vessel at the occipital branch of the left external carotid artery using embolic TRUFILL n-butyl cyanoacrylate.

The mass was completely excised subsequently and required superficial parotidectomy and with sacrifice of the FN. The left greater auricular nerve was then used for FN anastomoses via 12-7 jump graft to the left hypoglossal nerve. Final pathology of the mass revealed type I (chief) cells, which stained positive for chromogranin A and synaptophysin. An S-100 stain was also positive in scattered type 2 (sustentacular) cells.

Outcome and follow-up

One year postoperatively, the patient’s left face remained HB VI/VI and he exhibited significant left lagophthalmos that required he tape his left eye shut at night. He remained HB VI/VI on the left 2 years after his initial surgery and it was at this point that the patient elected to undergo facial reanimation surgery. Postoperatively, the patient reported drastic improvement in his symptoms. Overall the left facial nerve function was improved with his left forehead, eye and mouth, now HB IV/VI, HB II/VI and HB V/VI, respectively. The patient’s sloping mild-to-moderate sensorineural hearing loss in the 2000–8000 Hz frequencies on the left remained unchanged from the preoperative assessment.