Journal of Otology & RhinologyISSN: 2324-8785

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Case Report, J Otol Rhinol Vol: 5 Issue: 3

Misleading Clinical Presentation of the Superior Semicircular Canal Dehiscence Syndrome before Electrophysiological Testing and High Resolution Computed Tomography

Chiossone-Kerdel JA*, Graterón E, Ceballos S
Venezuelan Foundation of Otology, Venezuela
Corresponding author : Chiossone-Kerdel JA
MD MA FRCS, Calle Santa Cruz, Instituto Oto-Hospital. Urb Chuao, Caracas 1061 Apartado 62.277 Caracas 1060-A. Venezuela
Tel: +58 (412) 606-1202
E-mail: [email protected]
Received: February 25, 2016 Accepted: April 13, 2016 Published: April 18, 2016
Citation: Chiossone-Kerdel JA, Graterón E, Ceballos S (2016) Misleading Clinical Presentation of the Superior Semicircular Canal Dehiscence Syndrome before Electrophysiological Testing and High Resolution Computed Tomography. J Otol Rhinol 5:3. doi:10.4172/2324-8785.1000276

Abstract

The superior semicircular canal dehiscence syndrome is a recently reported condition. Superior semicircular canal bony coverage disruption presence determines his communication with the middle cranial fossa. The etiology is under continuous investigation. The paper objective is to describe with the presentation of two clinical cases, those elements that serves as a guide to the diagnosis of these infrequent and interesting disease and the challenge of not having the newest technological resources. The primary basis of the superior semicircular canal dehiscence syndrome diagnosis must rely on clinical suspicion supported by electrophysiological confirmation and millimetered temporal bone computed tomography

Keywords: Superior semicircular canal dehiscence syndrome; High resolution computed tomography

Keywords

Superior semicircular canal dehiscence syndrome; High resolution computed tomography

Introduction

The superior semicircular canal dehiscence syndrome (SSCDS) is a recently reported condition. Initially described by Minor, when study patients who showed vestibular and auditory symptoms, including oscillopsia, eye movements in response to intense auditory stimuli and hearing loss, with subsequent evidence of a disruption of the bone covering the superior semicircular canal of the affected ear through the use of computed tomography of the temporal bone [1]. Its pathogenesis is uncertain, postulating various theories framing from alterations in the embryonic development to posttraumatic alterations [2]. The absence of bone coverage at the superior semicircular canal (SSC) determines a communication between the canal and the middle cranial fossa creating a “third window phenomenon”, which in turn triggers audiological and clinical manifestations such as mixed hypoacusia with a conductive component in low frequencies, similar to that observed in the cochlear hydrops, in Meniere disease [1,3,4] . As for the vestibular symptoms such as nystagmus in response to intense auditory stimuli in the affected ear, called, the Tullio’s phenomenon, the “conductive hyperacusis”, which is the perception of eye movements in the affected ear due to an increase in the perception of bone threshold. Currently, there are diagnostic procedures that allows identifying this condition, it’s based on adequate physical examination, audiological assesment and studies such as vestibular evoked myogenic potentials (VEMPs), and finally high resolution computed tomography of the temporal bone (HRCT) with 0.5 to 1mm sections, demonstrating incomplete bone coverage of the superior semicircular canal [1,5]. The aim of these clinical cases is to describe, the presenting clinical condition in a patient who presented their first symptom 30 and 15 years ago.

Methods

Prior approval of the protocol by The Venezuelan Foundation Ethic Committee, clinical records of 2 patients with SSCDS were identified, a full description of signs, symptoms, audiology, electrophysiological tests and images is described.
Case 1
A 41- year-old male with bilateral Sudden Hearing Loss (SNHL) diagnosed 14 years before his first visit, associated with tinnitus and vertigo, treated with Prednisone in a pyramidal scheme and Betahistine, with a full left ear hearing recovery and 33 dB pure tone average (PTA) hearing loss in his right ear. He presented with hyperacusis, unsteadiness and vertigo after exposure to loud noises in his left ear in the last 5 months. Weber test lateralized to the left and Rinne was positive bilaterally to all frequencies, pure tone audiometry showed a mixed bilateral hypoacusia and speech discrimination was 100% in both ears ear (Figure 1). High-resolution Temporal bone computed tomography (HRTBCT) showed a disruption of the bony coverage of the left superior semicircular canal, vestibular evoked myogenic potentials (VEMPs) latencies showed left 15.67 milliseconds (ms) reduction in p1 wave, with an amplitude of 550.28 millivolts (mV) compared with the non-affected right ear of 16.34 ms and 94.82 mV (Figure 2A-C). Left ear is diagnosed with SSCDS and surgical obliteration of the superior semicircular canal using middle fossa approach was performed, with excellent results, given by absence of vertigo, and no left hearing loss, with audiometrics results same as preoperative at 8 months follow up.
Figure 1: Pure tone audiometry.
Figure 2A: Left sagittal HRCT cut, showing the SSC dehiscence.
Figure 2B: Left ear VEMP, showing the diminished latencies and increased amplitude.
Figure 2C: Right ear VEMP, showing normal latencies and amplitude.
Case 2
A 59-year-old female, diagnosed with Menière disease 31 years before her visit, received medical treatment without any significant recovery. The patient underwent left surgical endolymphatic sac decompression in 1986 and later the right side in 1991, with significant improvement in dizziness and progression of right hearing loss; later a progression in right hypoacusia with a conductive pattern was observed, Otosclerosis was diagnosed and a right stapedectomy was performed, with good audiological results initially but continuing with a progressive hearing loss (Table 1) without any vertigo or dizziness. Twenty-two (22) years after the last surgery, she referred autophonia, vertigo, nausea and vomiting in response to loud auditory stimulus in her left ear for the last 4 months. Weber was lateralized to her left ear and a Rinne bilaterally positive in all frequencies. PTA reported a slight sensorineural hearing loss in the right ear and no loss in the left, only a little decline in acute frequencies (Table 1 and 2). HRCT of the Temporal bone showed absence of bony coverage of the left superior semicircular canal (Figure 3). Despite the confirmed absence of the bony coverage of the canal, VEMPs results were not conclusive, with uncharacteristic findings (Figure 4A-B). A superior canal obliteration surgery via middle fossa approach was performed (Figure 5), without vertigo nor audiological changes 6 months post-operatively.
Table 1: Bone conduction Audiometry record.
Table 2: Air conduction Audiometry record.
Figure 3: Left sagittal HRCT cut, showing the SSC dehiscence.
Figure 4A: Left ear VEMP, showing the absence of waveform pattern.
Figure 4B: Right ear VEMP, showing the absence of waveform pattern.
Figure 5: Black bolded arrow pointing the dehiscence area during the middle fossa approach.

Discussion

The absence of the bony coverage of the superior semicircular canal directly communicates it with the middle cranial fossa producing important incapacitating symptoms to the patient. Etiology is not well understood, considering different hypotheses: abnormal postnatal development of the middle and outer layers of the bone canal, an erroneous disposition of primitive otocyst, alterations during the prenatal period, COCH gene mutations, increased intracranial pressure and eventually direct trauma [2].
The diagnosis is usually made during the fourth decade of life; however, a great range has been described from 13 to 70 years old. Both cases herein described are within the expected age for diagnosis; there is no specific prevalence in gender in all the revisited series [1,5,6].
Vestibular symptoms accounts for the primary complaint in both cases, as in other larger series, in fact Case 2 patient received endolymphatic sac surgery in both ears prior the diagnosis almost 30 years ago due to the similarity of the symptoms and based on a clinical diagnosis to indicate a surgical therapy. The improvement of the patient symptoms, causes the misleading diagnosis that can be demonstrated later due to the availability of HRCT and VEMPs. Mixed hearing loss pattern present in both cases, was much more evident after Case 2 surgery that mislead to a second diagnosis of Otosclerosis due to a low frequency conductive hearing loss and a surgery with marginal hearing results [1,4]. The unusual presentation of Case 1 with a history of bilateral SNHL with total recovery in one ear and a low frequency conductive hearing loss may be confused with cochlear hydrops, just in the vast majority of cases reported in the literature. The diagnosis in Case 1 was based in an electrophysiological test and HRCT scan, those, clearly demonstrate the typical SSCD findings [1,6]. These air-bone gap findings are probably due to dissipation of acoustic energy through a third mobile window [1,7]. Stapedial reflex testing were not found in both cases, although it is a simple and fast test, that needs to be done when an air-bone gap is found to rule out any conductive cause as a source of the gap, in cases of SSCD, results are always normal [1-3]. In Case 2 VEMPs were abnormal with a non-reproducible waveform, this may be due to repetitive surgeries in the inner ear such as endolymphatic sac surgery and stapedectomy, in this case her symptoms and HRCT were decisive to diagnose SSCD. The mechanism responsible for the lowered VEMP threshold in SSCDS patients is likely to also be related to the lowered impedance for transmission of sound and pressure stimuli created by the third mobile window. Thus, the VEMP stimulus in an ear with superior canal dehiscence results in larger activation of the sacculus with a large amplitude waveform than the normal ear [1].
Lowered thresholds for VEMP responses have also been reported in patients with enlarged vestibular and cochlear aqueduct [1,8,9] Endolymphatic sac surgery can resemble a similar condition, Case 2 had not normal waveforms to evaluate such changes. We found a reverse response in the right ear, even with a history of stapes surgery, there was a decreased latency and increased amplitude compared with the affected side [1], a situation that can be confusing and that only can be cleared by HRCT scan.
SSCD produce an increased sensitivity in bone-conduction (conductive hyperacusis) and autophony. The Weber test typically lateralizes to the affected ear due to this phenomena, which was present in both our cases [4].
Surgical procedure used to treat both cases were superior canal plugging with bone pate, fascia and muscle in the lumen of the canal, and cortical bone graft over the defect, with excellent outcome on the follow-up. This technique, transmastoid obliteration of the SSC, the most widely used for the surgeons with the largest published series, is an alternative surgical approach to this condition [9-11].

Conclusion

Diagnosis of SSCD was difficult without the electrophysiological and HRCT information we have now, some patients diagnosed in the past with Meniere’s or endolymphatic hydrops with poor response to medical and surgical treatment should be carefully re-evaluated to rule out the possibility of SSCD. In the presence of an air-bone gap in lower frequencies, stapedius reflexes and VEMP’s exploration are mandatory.

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