A Case of Facial Nerve Schwannoma Presenting as an External Auditory Canal Mass

다국어 초록 (Multilingual Abstract)

Introduction



Benign tumors, which originate from the peripheral nerve sheath that surrounds the axons of peripheral nerves, can be divided into two major groups: schwannoma and neurofibroma.1) Schwannoma is a tumor that originates from Schwann cells in the peripheral neurilemma, and approximately 25 percent of these tumors are known to occur in the head and neck region.2,3) The prevalence rate of facial nerve schwannomas is 1/23,000,4) and facial nerve schwannomas on the external temporal bone have been reported in 15% of all cases.5) The occurrence of facial nerve schwannomas in the middle ear and mastoid cavity is relatively rare. We report here on a case of schwannoma that originated from the mastoid segment of the facial nerve, which was presented as external auditory canal mass.


Case Report

A 24-year-old male patient presented to us a symptom in the right ear fullness, which had been occurring for a year. The ear fullness was felt only in the morning at first, but the pain had become severe in the last two to three months ago, and lasted all day. When he visited our hospital, there was a House- Brackmann Grade II facial nerve paralysis, and polyp-formed mass with a smooth surface that had filled the right external auditory canal. The eardrum could not be found due to the mass (Fig. 1). In pure-tone audiometry of 500 Hz, 1,000 Hz and 2,000 Hz, the right ear had an air conduction threshold of 35 dB HL and bone conduction threshold of 5 dB. In addition, the air-bone gap was 30 dB. In the computed tomography (CT) scan of the temporal bone, a shade of soft tissue that filled some of external auditory canal and mastoid was connected to the stylo-mastoid foramen. There were defects on the posterior wall of the external auditory canal due to the mass, but there were no specific ossicles and tympanic segment found on the facial nerve (Fig. 2). In the magnetic resonance image (MRI) T1 weighted image, the same relative signal strength and contrast enhancement with the brain parenchyma was observed and the mass, which was 1.3×1.4 cm, was connected to the part of the mastoid and stylo-mastoid foramen, through the external auditory canal (Fig. 3). It was diagnosed as schwannoma in preoperative incisional biopsy results, which were positive for S-100 protein staining. The dia-gnosis was facial nerve neurilemmoma, which caused the conductive hearing loss and invaded the entire external auditory canal and the middle ear. Surgery was performed using the transmastoid approach. The mass in the external auditory canal was connected to the part of the epitympanum and the mastoid cavity, along the posterior wall of external auditory canal. The mass started at the second genu of the facial nerve, and was connected to the stylomastoid foramen across the entire mastoid segments. However, It had a distinct border with the tympanic segment, so it was relatively easy to dissect. After resection of the mass, neurorraphy with the great auricular nerve was performed using a 9-0 nylon suture. After Tissue glue (Tisseel kit® 2 mL, Baxter) was applied to the connected nerves, we covered the nerves with tragal cartilage, tragal perichondrium and temporalis muscle fascia, and obliterated the opening with an inferior based musculocutaneous flap (Fig. 4). Keratin had gathered began to form a cholesteatoma in the external auditory canal that was inside of the mass. In addition, part of the tympanic membrane was lost due to the mass but the ossicles were intact. In the histopathologic report, Antoni type A, which are the spindle cells, and the surrounding connective tissues were well-arranged, and Antoni type B, which has relatively loose phlegmatic temparament, were scattered. Thus, this case was diagnosed as a typical schwannoma, which was positive for S-100 protein staining (Fig. 5). He had no symptoms such as dizziness after the surgery. It has been 3 months since the surgery and the facial nerve palsy of patients is House-Brackmann Grade III (...

다국어 초록 (Multilingual Abstract)

Facial nerve schwannoma is a rare benign tumor that arises from the Schwann cell sheath of facial nerve. Although the tumor can occur anywhere along the course of the peripheral nerve, it is frequently present as an internal auditory canal mass in the head and neck region. We experienced a rare case of facial nerve schwannoma on the mastoid segment, which was presented as an external auditory canal mass in a 24-years-old man. The lesion was removed via the transmastoid approach and the facial nerve was grafted using the greater auricular nerve. The patient's facial nerve function was preserved postoperatively as House-Brackmann grade III

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