A 60-year-old man presented with hearing loss and a history of fluctuating facial weakness and synkinesis. He reported having an episode of facial paralysis many years ago, but he recovered with some mild residual weakness. Since then, he had also developed mild synkinesis (eye closure with mouth movement). Physical exam of his right ear revealed a grade I retraction of the pars flaccida and a white mass in the posterosuperior quadrant behind the tympanic membrane; his left ear was normal. He exhibited some facial weakness in the lower face and twitching of the eyelid with mouth movement. The rest of his head and neck exam results were normal. His audiogram (Fig. 1) is on the right. Tympanogram showed type As on the right.
Diagnosis: Facial Nerve Schwannoma
The patient's combined presentation of conductive hearing loss, a visible mass, and facial nerve changes was concerning for a pathology beyond ossicular fixation (e.g., otosclerosis). Facial nerve symptoms, including weakness, drooping, asymmetry of the facial muscles, and synkinesis (when the movement of one muscle triggers the involuntary movement of another muscle, such as this patient's eyelid twitch upon mouth movement) suggest a process involving not only the ossicular chain but also the facial nerve.1 This patient's physical exam findings were most consistent with a mass affecting the middle ear and facial nerve, the true extent of which is best evaluated with a combination of computed tomography (CT) and magnetic resonance imaging (MRI). From a statistical standpoint, a cholesteatoma was most likely the white mass that was causing conductive hearing loss and facial weakness. The patient had not had previous ear surgery and had no deep retraction in the tympanic membrane, which made an acquired cholesteatoma unlikely. At 60 years of age, however, a congenital cholesteatoma was very unlikely. Also, facial paralysis caused by a cholesteatoma rarely recovers unless it is acutely treated and removed. Synkinesis indicates degeneration and regeneration, which made cholesteatoma unlikely.
CT imaging can provide extensive details of bony anatomy and be useful for evaluating the size and location of middle ear abnormalities. A CT of this patient's temporal bone showed a mass medial to the malleus and incus that extended into the mastoid (Figs. 2-4). If a neoplasm is seen on CT, an MRI is usually obtained next since it gives a detailed view of soft tissues and helps distinguish certain types of neoplasms from inflammation or scar tissue. This patient's MRI showed a large extratemporal and fully encapsulated component of the neoplasm that extended into the parotid gland (Figs. 5-6). The mass also involved the middle ear, mastoid, stylomastoid foramen, and parapharyngeal space.
The differential diagnosis for this patient's mass, which involved the facial nerve from the middle ear to the parotid and parapharyngeal space, included primary facial nerve tumor (e.g., facial schwannoma) and tumor with perineural invasion (e.g., squamous or basal cell carcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma), among others. Clinicians should be cautious of labeling chronic facial nerve symptoms as Bell's palsy or atypical Bell's palsy since many types of malignant and non-malignant neoplasms can cause facial nerve symptoms.
In this patient's case, the mass was likely a facial schwannoma, also incorrectly called a facial neuroma, which is a benign tumor that originates from the Schwann cells and wraps around neurons. A neuroma is a nerve tumor, whereas a schwannoma is a nerve sheath tumor. A few distinguishing features helped lead us to this conclusion. First, a well-encapsulated mass with defined borders, as in the case of this patient, is often benign. Second, the presence of synkinesis suggested that the facial nerve was damaged but had regenerated—a process often seen in facial schwannomas. When the nerve regenerates, some nerve fibers can cross over and get miswired, resulting in involuntary muscle contractions with certain unrelated muscle movements. Cancers involving the facial nerve gradually cause permanent paralysis. It is highly unlikely that the facial nerve would regenerate after a cancer has invaded the nerve. Since facial schwannomas are nerve sheath tumors, the axons are only damaged if applied with pressure. If the tumor compresses the axons i-nside the bony canal of the facial nerve, it can cause permanent weakness. However, as the tumor grows slowly, it tends to take the path of least resistance where it can grow without outside pressure. The tumor tends to grow outside of the mastoid, intracranially, and into the middle ear. Facial hemangiomas can cause this issue, but they are isolated to a small area of the facial nerve.2
Facial schwannomas are similar in origin and nature to the much more common vestibular schwannomas. Whereas vestibular schwannomas are tumors of the myelin sheath-forming the Schwann cells of the vestibulocochlear nerve, facial schwannomas are tumors of the Schwann cells of the facial nerve. Both are benign but can cause symptoms via mass effect. Facial schwannomas can occur along the entire course of the facial nerve, but they most commonly occur along the temporal segment or around the geniculate ganglion. They can cause facial weakness or paralysis, often slowly progressive, and audiovestibular symptoms, including hearing loss, vertigo, and tinnitus. From its origin in the pons, the facial nerve passes through the internal auditory canal and the temporal bone before exiting the skull at the stylomastoid foramen and splitting into five motor muscle branches in the parotid gland. Because of this winding course, facial schwannomas can cause a variety of mass effect symptoms over vast regions, including the ear, upper neck, and parotid areas.
Management of facial schwannomas is mainly determined by the severity of hearing and facial symptoms or the degree of local erosion. If the patient exhibits proper facial and hearing function, conservative management with observation is preferable. Because surgical removal of the tumor almost always causes loss of facial function, it is only done when facial function is already lost, in cases of severe hearing loss, or if local destruction or erosion is threatening vital structures. Other less radical surgical options include debulking or decompression of the nerve. More recently, stereotactic radiosurgery, which uses multiple focused radiation beams to target specific tissues, has been used with great success in managing facial schwannomas.
Because this patient continued to have good facial function with only mild weakness, he chose a conservative management option, which was to continue observing his condition. If his facial function declines or his hearing loss worsens, he may benefit from radiosurgery or surgical excision with reconstruction of the facial nerve using the sural nerve (from the lower leg). In the future, a device in development can help with the rehabilitation of the facial nerve.3-5
BONUS ONLINE VIDEOS: VISUAL DIAGNOSIS
Read this month's Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient's imaging for yourself.
- Video 1. Axial (horizontal) CT of the temporal bones showing the mass medial to the ossicles.
- Video 2. Coronal (vertical parallel to the face) CT of the temporal bones showing the mass and its relationship to the horizontal canal and the cochlea.
- Video 3. Sagittal (vertical parallel to the ear) CT of the temporal bones demonstrating the mastoid component of the tumor.
- Video 4. Axial (horizontal) T1-weighted post-contrast MRI of the brain showing the mass and its extratemporal areas.
- Video 5. Coronal (vertical parallel to face) T1-weighted post-contrast MRI of the brain showing the extension of the mass off the stylomastoid foramen.
- Video 6. Sagittal (vertical parallel to ear) T1-weighted post-contrast MRI of the brain showing the tumor in the sagittal plane.
Watch the patient videos online at thehearingjournal.com.
1. Vrabec JT, Backous DD, Djalilian HR, et al. Facial Nerve Grading System 2.0. Otolaryngol Head Neck Surg
. 2009 Apr;140(4):445-50.
2. Wu EC, Rothholtz VS, Zardouz S, Lee AD, Djalilian HR. Facial nerve hemangioma: a case report. Ear Nose Throat J.
3. Sahyouni R, Bhatt J, Djalilian HR, Tang WC, Middlebrooks JC, Lin HW. Selective stimulation of facial muscles with a penetrating electrode array in the feline model. Laryngoscope.
4. Sahyouni R, Haidar YM, Moshtaghi O, Wang BY, Djalilian HR, Middlebrooks JC, Lin HW. Selective Stimulation of Facial Muscles Following Chronic Intraneural Electrode Array Implantation and Facial Nerve Injury in the Feline Model. Otol Neurotol.
5. Askari S, Presacco A, Sahyouni R, Djalilian H, Shkel A, Lin H. Closed Loop Microfabricated Facial Reanimation Device Coupling EMG-Driven Facial Nerve Stimulation with a Chronically Implanted Multichannel Cuff Electrode. Conf Proc IEEE Eng Med Biol Soc.