Symptoms: Sudden Sensorineural Hearing Loss and Aural Fullness

A 40-year-old man presented to our clinic with left-sided sudden sensorineural hearing loss and aural fullness. He also complained of left tongue numbness and a metallic taste in the mouth. He denied tinnitus, otalgia, and dizziness. He denied any facial weakness, pain, or numbness. He denied hemifacial spasm, dryness or tearing of the eyes, swallowing difficulty, or hoarseness. The patient had been treated with oral and intratympanic steroids with no improvement in hearing. An audiogram showed profound hearing loss with no measurable audiometric thresholds in the left ear. There was no sign of ptosis. The microscopic exam of the bilateral ears did not show significant findings. The audiogram showed a profound left hearing loss. The MRI image of the patient is to the right (see Figure 1).Figure 1: Axial (horizontal) T1-weighted post-gadolinium MRI showing a bilobed mass with dilation of the left internal auditory canal (IAC) and a narrow porus acusticus with a sizeable cerebellopontine angle (CPA) portion.Figure 2: Coronal (parallel to the face) post-gadolinium T1-weighted MRI of IAC showing the bilobed tumor with a narrow (normal sized) IAC segment in between.Figure 3: Coronal (parallel to the face) post-gadolinium T1-weighted MRI of IAC showing the tumor extending above the cochlea laterally and in contact with the cochlea.Figure 4: Coronal (parallel to the face) CISS sequence MRI of IAC showing the tumor extending above the cochlea laterally and in contact with the cochlea.Figure 5: Axial (horizontal) CT of the left temporal bone showing dilated IAC with erosion intro the petrous apex air cells.Figure 6: Coronal (parallel to the face) CT of the left temporal bone demonstrating the erosion of the tumor into the cochlea and the dilation of the labyrinthine segment of the facial nerve.Diagnosis: Facial Schwannoma When a patient presents with unilateral hearing loss associated with otologic symptoms such as aural fullness, clinicians should consider a mass within the inner ear, the internal auditory canal (IAC), or the cerebellopontine angle (CPA) in the differential diagnosis. Other differential diagnoses include migraine; Meniere’s disease; cholesteatoma; and infectious, autoimmune, neoplastic, or traumatic etiologies. Thus, it is imperative to get a thorough medical history, examination, and to obtain magnetic resonance imaging (MRI) of the internal auditory canals to help determine the etiology behind the patient’s presentation. A cholesteatoma produces a low signal intensity on T1-weighted MRI and high signal intensity on T2-weighted MRI. However, since the patient had no history of ear surgery or deep retraction of the tympanic membrane on examination, acquired cholesteatoma was unlikely. In contrast to cholesteatoma lesions, which do not enhance on postcontrast MRI, schwannomas are diffusely enhancing lesions that appear hypo- to isointense to the brain on T1-weighted MRI. Vestibular schwannomas represent 8% of intracranial tumors, whereas facial schwannomas account for less than 1% of all temporal bone tumors. When confined to the IAC or CPA without the involvement of the labyrinthine portion of the facial nerve or geniculated ganglion, the distinction between vestibular schwannoma and facial schwannoma cannot be easily made preoperatively. For this patient, we obtained an MRI of the IACs (Figures 1-4), which showed an enhancing bilobed mass centered within the CPA. The mass extends through the porus acusticus (medial opening of the IAC through which the vestibulocochlear nerve, facial nerve, and labyrinthine artery pass), to the IAC, and medially abuts the brainstem. The mass displaces the left pons and middle cerebellar peduncle. The tongue changes are due to involvement of the nervus intermedius which joins the facial nerve and carries the taste fibers as well as the parasympathetic fibers to the nose and sinuses, submandibular, and sublingual glands. A temporal CT scan (Figures 5-6) was also obtained, which further revealed the mass with a widening of the IAC and labyrinthine segment of the facial nerve. Furthermore, there are areas of bony dehiscence of the anterior wall of the IAC and posterior aspect of the left petrous apex with a communication to the middle fossa. At first sight, the tumor suggests a vestibular schwannoma. However, it is not common for a vestibular schwannoma to extend above the internal auditory canal anteriorly and laterally above the cochlea, which indicates that this likely represents a facial nerve tumor. Therefore, the patient underwent facial electromyography (EMG). Facial nerve EMG testing showed a 30% loss in the upper face and 50% loss in the lower face indicating likely facial schwannoma. Given the clinical presentation, imaging findings, and EMG results, the patient was diagnosed with facial schwannoma. Facial schwannomas are rare benign tumors that arise from the Schwann cells of the facial nerve. These tumors are slow-growing and usually asymptomatic until they grow enough to compress nearby structures. The most common clinical manifestation includes facial paresis due to the compression of the facial nerve by the tumor. Sensorineural and conductive hearing loss, otalgia, and dizziness can also be present due to the proximity of the mass to the middle and inner ear structures. When isolated intracranially, facial schwannomas are difficult to distinguish from vestibular schwannomas and meningiomas, unless they involve the geniculate ganglion, tympanic, mastoid, or parotid portion of the nerve. Several treatment options exist for facial nerve schwannoma depending on its size, rapidity of growth, presence of symptoms, and patient’s age and comorbidities. For patients with slow-growing tumor and normal facial nerve function, “wait and see” with serial imaging is sometimes recommended. Once the patient exhibits signs of facial nerve dysfunction or brainstem compression, surgical resection with facial nerve reconstruction, surgical decompression of the IAC with radiosurgery, or stereotactic radiosurgery should be considered. 1 Surgical removal can be performed through different techniques such as retrosigmoid, middle fossa, or translabyrinthine approaches. The middle fossa approach is preferred in small tumors and is advocated when hearing preservation is possible. The retrosigmoid approach is used for tumors isolated to the posterior fossa and IAC. Finally, the translabyrinthine approach is preferred for patients who have no useful hearing and balance function. To delay surgical resection, facial nerve decompression could be performed to allow the tumor within the bony confines of the temporal bone to expand; thus, relieving the symptoms caused by the tumor compression on axons of the facial nerve. 2 Another option to consider includes stereotactic radiosurgery, either in a single session with GammaKnife or in multi-sessions with CyberKnife. It is a minimally invasive procedure that has been widely used due to its success in long-term tumor control and functional outcomes (facial nerve function and hearing preservation). 3 In the past, surgical resection was carried out when the patient developed facial paralysis as facial reconstruction techniques at best can achieve a grade 3 out of 6. However, more recently, more patients undergo radiosurgery if the facial function is normal. Given the patient’s age and the tumor size, location, and mass effect on the brainstem (Koos grade 4), observation is not an option. The IACs are very narrowed at the porus acusticus that any swelling of the facial nerve after radiosurgery would likely increase the risk of facial weakness. Therefore, we recommended IAC decompression followed by stereotactic radiosurgery. 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) post-gadolinium T1-weighted MRI of IAC showing the tumor. Video 2. Coronal (parallel to the face) post-gadolinium T1-weighted MRI of IAC showing the tumor extending above IAC laterally. Video 3. Coronal (parallel to the face) CISS sequence MRI of IAC showing the tumor extending above IAC laterally and in contact with the cochlea. Video 4. Axial (horizontal) T2 CISS sequence MRI of IAC demonstrating the extension of the tumor above the cochlea. Video 5. Axial (horizontal) CT of left temporal bone showing dilated IAC with erosion into the petrous air cells. Video 6. Coronal (parallel to the face) CT of the left temporal bone demonstrating the erosion of the tumor into the cochlea and the dilation of the labyrinthine segment of the facial nerve. Watch the patient videos online at thehearingjournal.com.