Symptom: Unilateral Facial Paralysis

Abstract

A 28-year-old man presented with right-sided facial paralysis that had been worsening over the past eight months. He was initially diagnosed with Bell's palsy and treated with oral steroids and antiviral medication immediately after symptom onset, but experienced minimal improvement. He has a known history of conductive hearing loss in the right ear since age five due to a traumatic tympanic membrane perforation from q-tip use and subsequently underwent tympanoplasty at that time. He denied otalgia, otorrhea, vertigo, or tinnitus. Physical examination showed grade 6/6 paralysis on the right side. Audiogram from two months before presentation ago is shown in Figure 1. What is your diagnosis?Figure 1: Audiogram showing moderate-to-severe conductive hearing loss on the right side. Hearing loss, paralysis.Figure 2: Axial (horizontal) CT of the right temporal bone showing the cholesteatoma involving the middle ear, cochlea, and internal auditory canal. Hearing loss, paralysis.Figure 3: Axial (horizontal) CT of the right temporal bone showing cholesteatoma 1.2 mm above Figure 2 showing the involvement of the tympanic (middle ear) facial nerve by the cholesteatoma. Hearing loss, paralysis.Figure 4: Coronal (vertical parallel to ear) CT of the right temporal bone demonstrating that the cholesteatoma has eroded the tegmen tympani. The cholesteatoma appears to have originated medial to the malleus. Hearing loss, paralysis.Figure 5: Sagittal (vertical parallel to face) CT of the right temporal bone further highlighting the erosion of the tegmen tympani as the cholesteatoma extended medially to the cochlea and internal auditory canal. Hearing loss, paralysis.Figure 6: Sagittal (vertical parallel to face) CT Temporal bone showing the involvement of the cochlea 2 mm medial to the image in Figure 5. Hearing loss, paralysis.DIAGNOSIS: IATROGENIC CHOLESTEATOMA The most concerning aspect of this patient's presentation is the duration of his facial paralysis. Although Bell's palsy is the most frequent diagnosis for facial paralysis, the physician must begin to consider other etiologies and obtain imaging with MRI of the internal auditory canals (IACs) if the paralysis persists beyond six months. The majority of patients with facial paralysis are diagnosed with Bell's palsy, also called idiopathic facial nerve paralysis. By definition, the exact cause of Bell's palsy is unknown; however, it is believed that a large number of cases are due to edema in and around the facial nerve and is caused by the herpes simplex virus (HSV). HSV, which also causes cold sores, has been found to be present within the geniculate ganglion of affected individuals. Viral replication and reactivation within the ganglion are thought to cause edema and subsequent compression of facial nerve fibers, resulting in blockage of electrical conduction and subsequent facial paralysis. The surrounding bony architecture of the facial nerve helps to explain this phenomenon. As it courses through the labyrinthine segment of the temporal bone (the narrowest portion of the fallopian canal measuring approximately 0.68 mm), the facial nerve is completely surrounded by bone, and therefore vulnerable to compression in the event of swelling. The extent of nerve injury depends on both the degree of inflammation and how quickly treatment with steroids and antivirals can be given to reduce swelling. In cases of mild edema, there is transient compression and blockage of nerve conduction until the inflammation subsides. However, in more severe cases the nerve fibers may be crushed and rapidly degenerate. In these cases, axon regeneration usually occurs, but the new nerve fibers may not reach the intended target muscles. This results in synkinesis, in which voluntary movement in one facial muscle group causes involuntary activity of another. For example, a patient may experience involuntary blinking when trying to smile. In the case of this patient, we obtained a CT scan of the temporal bones given the history of conductive hearing loss and previous surgery (Figs. 2, 3, 4, 5). On the right side, we see bony erosion with soft tissue opacification within the petrous and mastoid temporal bone segments, including regional involvement of the labyrinthine and tympanic segments of the facial nerve, basal turn of the cochlea, vestibule, IAC, tegmen tympani, and middle ear cavity including the ossicles. Though initially treated for Bell's palsy, our patient was ultimately diagnosed with a middle ear cholesteatoma that invaded the skull base and involved the facial nerve. The diagnosis was confirmed surgically. Cholesteatomas are benign masses comprised of abnormal squamous epithelium within the temporal bone. Over time, these masses can grow large enough to cause local bony destruction with surrounding inflammation and granulation tissue. Cholesteatomas are often classified into congenital and acquired types (primary or secondary). In the primary acquired type, cholesteatomas typically arise in the setting of chronic tympanic membrane (TM) retraction. Alternatively, secondary acquired cholesteatomas occur in the setting of TM perforation with epithelial migration into the middle ear space. Given the patient's history of q-tip injury and subsequent surgery, the cholesteatoma was most likely caused by traumatic implantation of squamous epithelium or iatrogenic, i.e., caused by the surgeon not removing or implanting squamous epithelium from the middle ear. Facial nerve palsy due to cholesteatoma has been rarely reported in the literature.1 While the mechanism by which cholesteatoma causes facial nerve palsy remains unclear, several theories have been proposed. The first hypothesis is that direct compression by the cholesteatoma is responsible for causing nerve edema and subsequent ischemia. A second hypothesis is that direct contact between the cholesteatoma and facial nerve promotes an inflammatory reaction that leads to injury. This theory is supported by histological studies showing degeneration of the epineurium in facial nerve segments exposed to cholesteatoma or granulation tissue.2 A third hypothesis is that nerve injury is mediated by neurotoxic or enzymatic substances secreted by the cholesteatoma, although the significance of these factors remains controversial.3 It is important to accurately diagnose and treat cholesteatomas, as they have a strong propensity to become infected and erode through local bony structures.4 The infections and associated pathogens in cholesteatoma can be especially hard to eradicate as they are frequently polymicrobial and resistant to antibiotics. Skull base invasion of cholesteatomas carries an increased risk of deafness, facial paralysis, and intracranial complications given their location. In this patient, we see the cholesteatoma is already eroding the cochlea, creating an increased likelihood of sensorineural hearing loss in the right ear. After evaluating the extent of the disease on CT scan, surgical treatment is undertaken with the goals of removing all of the cholesteatoma and repairing damaged structures when possible. Various surgical approaches can be used, depending on the involved structures as well as surgeon comfort level. In this patient, a right middle cranial fossa or translabyrinthine approach could be undertaken. Generally, when the hearing is intact, the best approach is the middle cranial fossa. The translabyrinthine approach is reserved for non-serviceable hearing patients. If the facial nerve function does not return, the patient may receive a hypoglossal-facial jump graft. In the future, a medical device in development may allow restoration of function for the patient.5-6 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 right temporal bone showing the extent of the cholesteatoma in the axial plane and involvement of tympanic facial nerve and geniculate ganglion. Video 2. Coronal (vertical parallel to ear) CT of the right temporal bone showing the extent of the cholesteatoma in the coronal plane and invasion of the tegmen and IAC. Video 3. Sagittal (vertical parallel to face) CT of the right temporal bone showing the extent of the cholesteatoma in the sagittal plane and invasion of the cochlea. Video 4. Axial (horizontal) CT of the left temporal bone showing the normal anatomy of the facial nerve in the axial plane. Video 5. Coronal (vertical parallel to ear) CT of the left temporal bone showing the normal anatomy of the tegmen tympani. Video 6. Sagittal (vertical parallel to face) CT of the left temporal bone showing the normal cochlear anatomy in the sagittal plane. Watch the patient videos online at thehearingjournal.com