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Address for correspondence : Dae Bo Shim, MD, Department of Otorhinolaryngology, Kwandong University College of Medicine, 697-24 Hwajeong-dong, Deogyang-gu, Goyang 412-270, Korea
Tel : +82-31-810-5407, Fax : +82-31-969-0500, E-mail : lovend77@gmail.com
Introduction
Although the etiology and pathophysiology of sudden sensorineural hearing loss (SSNHL) remains unclear, a commonly used criterion is a sensorineural hearing loss (SNHL) of greater than 30 dBHL over three contiguous pure tone frequencies occurring within 3 days period.1) Since the report by De Kleyn in 1944, the precise cause and prognosis have not been well-understood, widely ranging from the spontaneously recovering hearing loss to no response to any treatments.2) As some hold that this disease is generally idiopathic, the differential diagnosis includes head trauma, viral infection, vascular abnormalities, intracochlear membrane rupture, autoimmune disease and acoustic neuroma.1,2,3) It has been reported that 4.2% of all SSNHL results from the trauma, classified into skull fracture, barotrauma, trauma after the water irrigation and acoustic trauma.4,5) Here, we report two cases of SSNHL caused by the head trauma with consideration of the pathophysiology of the blunt trauma-related SSNHL.
Case Report
Case 1
A 60-year-old female presented to the emergency department following a tumble down some stairs. Symptoms of unilateral right side hearing loss, tinnitus, ear fullness, headache and dizziness with vomiting prompted to admit the patient to the otolaryngology department. Without any specific history of illnesses except for hypertension, spontaneous nystagmus of vertical oscillating movements was the only obvious finding in a neuro-otological exam. Bilateral positive sign in the Rinne test and the left lateralization in the Weber test implied SSNHL of the right side. In a Romberg test conducted to determine cerebellar functions, the patient had a tendency of falling to the right side after 2 seconds. No notable findings were identified by magnetic resonance imaging (MRI) of the internal auditory canal (IAC), which was carried out for the differential diagnosis from a retrocochlear lesion. As well, no fracture or middle ear effusion was observed by temporal bone computed tomography (CT). Complete blood count, erythrocyte sedimentation rate, blood glucose, blood coagulation test, serum test and thyroid function test were all negative. No specific results were obtained in an otoscopic examination, but a pure tone audiometry test carried out on the second day of admission demonstrated that the average auditory threshold was up to 100 dBHL, indicative of profound SNHL. The left side was normal (Fig. 1A).
On the second day morning of admission, left beating spontaneous nystagmus with torsional component was observed in the video nystagmography (VNG). After head shaking, the degree of left beating nystagmus was augmented. On day 3 following admission, the torsional component in spontaneous nystagmus disappeared and compensatory saccadic eye movement when rotating the head to the right in a head thrust test were found. On day 4, there was no change in VNG, and, beginning in the afternoon, the amplitude of spontaneous nystagmus decreased. Since day 5, the amplitude of spontaneous nystagmus markedly decreased with no corrective saccade in head thrust test and notably reduced symptoms of dizziness. With regard to these findings, head trauma was thought to be the trigger of sudden right side hearing loss and labyrinthine concussion. The patient was given a 5-day course of prednisolone (1 mg/kg/day) from the first day of admission, tapering down during the 5-days. Tanamin (80 mg every 12 hr) and Eglandin (10 µg once a day) were also injected from the first day for vascular problems. The dizziness began to resolve on day 4. There was no response evoked on the right ear in a vestibular evoked myogenic potential (VEMP) test (Fig. 2A). Caloric testing revealed a decreased caloric response of 100% in the right side compared to the left side (Fig. 2B). The patient was discharged on day 7 and re-visited as an outpatient 14 days following the appearance of symptoms. No further improvement of the past profound-status of the right side was apparent in a pure tone audiometry test conducted on the re-visit. Nine months later, a pure tone audiometry test showed no recovery of hearing, despite five cycles intratympanic dexamethasone (5 mg/mL) injections on day 14 (Fig. 1B).
Case 2
A 48-year-old male career soldier visited as an outpatient complaining of tinnitus, hearing loss of the left ear and mild dizziness immediately after sustaining a blow to the left ear 3 months previously. Underestimating the severity of the symptoms at their onset, the patient did not see the doctor. The patient was diagnosed with profound hearing loss at a military hospital 1 month previous to the outpatient visit, but declined treatment. The otoscopic finding on the day of the outpatient visit was unremarkable. Pure tone audiometry measured the auditory threshold to be 15 dB for the right ear and 86 dB for the left ear, indicating severe SNHL (Fig. 3A). The finding of IAC MRI and temporal bone CT was unremarkable. Blood tests were all negative. On the first day of admission, weak horizontal spontaneous nystagmus toward the right side was observed in the VNG and a head shaking test revealed nystagmus increasing to the right, but dizziness was absent. The patient was given a same management with case 1 patient because the patient wanted treatment due to slightest possibility of remission, although the onset of treatment was very late. There was no response evoked on the left ear in the VEMP test (Fig. 4A). Caloric testing revealed a decreased caloric response of 100% in the left side compared to the right side (Fig. 4B). The patient was discharged because of personal affairs on day 3. No improvement was apparent at a follow-up 10 days later; the auditory threshold was still 91 dB in pure tone audiometry (Fig. 3B).
Discussion
Both the cited cases of SSNHL and dizziness had a history of mild head trauma in common with the total hearing and vestibular loss verified by functional tests. Every examination result was the same except for the degree of dizziness and hearing loss, which were more severe in the case 1 patient. No significant evidence of temporal bone fracture and otic capsule damage was found by imaging in both patients; retrocochlear lesion was absent and blood tests were negative. Caloric testing revealed a decreased caloric response in the ipsilateral side compared to the contralateral side. VEMP testing revealed non-response in the ipsilesioned ear. Several theories about etiologies could be concluded on the base of these two case-studies.
The postulated pathophysiology for the SSNHL with dizziness after head trauma has four possible pathways. First, microfractures resulting from the head trauma could account for the labyrinthine concussion. However, they were not big enough to be identified by imaging. Traumatic perilymph fistula, a destruction of central auditory structure, might also be an important etiology. The likelihood of simultaneous acute labyrinthitis is a slim one but cannot be excluded.
Head trauma does not impart just a simple shock. Various damages are possible, ranging from the inner ear structural and neurological damage to brain laceration and hemorrhage.6) Microfractures in the otic capsule might directly cut across the ossicles or cochlea. Microfracture cutting across the ossicles almost produces conductive hearing loss, and so can be ruled out in the present two cases. However, a cochlear microfracture is compatible with SNHL. Hemorrhage caused by a microfracture of the bony labyrinth might seep through the peri- or endo-lymph, degenerating the neuroepithelium, resulting in a labyrinthine concussion. In such a case, however, it is unlikely that imaging would detect the lesion, which might later be classed as an
'idiopathic etiology'.
Another possible explanation of SSNHL is a traumatic perilymph fistula. Considering the increasing incidence of traumatic perilymph fistula, it cannot be ignored merely on the basis of its rarity.7) Considerable controversy still exists regarding the cause and pathophysiology of traumatic perilymph fistula. But, two speculated causes are external and internal explosions. The former is a tension-induced pressure transmission through cochlear aqueduct or IAC, which leads to oval window rupture or dislocation of the lagamentum anulare stapedis. The latter is a sudden external pressure difference that passes through the eustachian tube, bursting round window and internally dislocating the stapedial foot plate.8) The traumatic perilymph fistula of an external explosion might be responsible for the symptoms of the case 1 patient. This patient experienced the sudden hearing loss and the long-lasting, sustained positional torsional nystagmus that changed over time, and had no reverse nystagmus when sitting up with relatively severe dizziness. Hence, It is considered that the possibility of traumatic perilymph fistula is high in case 1 patient. Although an exploratory tympanotomy should have been performed for the definite diagnosis, the procedure was not performed in case 1 patient because of the recovery of her vertigo on the day 4 of admission. However, relatively sensitive examinations such as fistula tests and imaging tests should be done for further differential diagnosis in such a case.
The damage of peripheral auditory structure is usually accompanied by head trauma. Moreover, damage of the central auditory structure should also be addressed concerning the likelihood of the broad brain damage. Such damage might be primarily due to either direct impact on the middle and inner ear, or rupture of the central neural pathway.6) Head trauma not only elongates of neural fibers but also devastates the intracochlear fibroblasts by transmission of compressive force to the inner ear, which finally leads to SSNHL.9,10) In a practical animal model (cat), a shock delivered to the inner ear destroyed the organ of Corti, spiral ganglion, spiral lamina, basement membrane and perilymph space.10) Besides a shock alone, the likelihood of cochlear microcirculation failure and membrane damage caused by inflow of mild hemorrhage is not subtle.
The last theory, which is least likely, involves simultaneous acute labyrinthitis. The two present case studies did not provide convincing evidence of acute inflammation and abnormalities in the physical exams; thus, this last possibility can be ruled out in our cases. However the possibility of simultaneous acute labyrinthitis must be considered in all traumatic SSNHL patients.
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