|Year : 2018 | Volume
| Issue : 2 | Page : 262-264
Superior semicircular canal dehiscence syndrome: An uncommon cause of vertigo
Santosh Kumar Swain1, Alok Das1, Mahesh Chandra Sahu2
1 Department of Otorhinolaryngology, IMS and SUM Hospital, Siksha “O” Anusandhan (Deemed to be University), Bhubaneswar, Odisha, India
2 Department of Research, Central Research Laboratory, IMS and SUM hospital, Siksha “O” Anusandhan (Deemed to be University), Bhubaneswar, Odisha, India
|Date of Web Publication||27-Dec-2018|
Prof. Santosh Kumar Swain
Department of Otorhinolaryngology, IMS and SUM Hospital, Bhubaneswar - 751 003, Odisha
Source of Support: None, Conflict of Interest: None
Superior semicircular canal dehiscence syndrome (SSCDS) is a rare and recently described inner ear lesion presenting with disequilibrium and associated with dehiscence of the bony covering of SSC. SSCDS patients may present with a variety of vestibular or auditory symptoms or both. The diagnosis of SSCDS depends on the demonstration of a defect in the bony wall of the roof of SSC. A high-resolution computed tomography is helpful for diagnosis. It is usually treated by plugging of dehiscence. We hereby present a rare cause of disequilibrium and SSCDS, diagnosed by clinical presentations, audiological tests and imaging.
Keywords: Superior semicircular canal, superior semicircular canal dehiscence syndrome, vertigo
|How to cite this article:|
Swain SK, Das A, Sahu MC. Superior semicircular canal dehiscence syndrome: An uncommon cause of vertigo. Arch Med Health Sci 2018;6:262-4
| Introduction|| |
Superior semicircular canal dehiscence syndrome (SSCDS) is rare clinical entity characterized by vestibular symptoms in response to loud sound or change in intracranial or middle ear pressure due to dehiscence of bony plate covering the SSC. SSCDS was first described by Lioyd Minor in 1998. It is an uncommon clinical entity with prevalence of 0.5%, which represents a set of clinical, vestibular, and cochlear symptoms associated with dehiscence of bony covering at the roof of SSC. Due to the formation of third window of the inner ear, it leads to dissipation of the acoustic energy of sound waves, abnormal mobility of endolymph and reduced threshold of bone conduction. These phenomena lead to pseudoconductive hearing loss, vertigo/imbalance and autophony. The exact etiology is still unknown. Few patients of SSCDS present with only hearing loss without any vestibular symptoms. Superior semicircular canal dehiscence (SSCD) is the discontinuity of the bony overlying of SSC making a third window of the inner ear. Here, we are presenting a case of SSCDS in a 45-year-old male.
| Case Report|| |
A 45-year-old male attended the outpatient department of otorhinolaryngology with complaints of spinning sensation during inserting his finger in the right ear for 3 months. He had also the same complaint during exposure to loud noise. He also complained hearing loss in the right side for 3 months. There was no past history of head injury or ear discharge. On investigations, pure-tone audiogram revealed a moderate degree of conductive hearing loss with air-bone gap whereas normal hearing in the left side. Impedance audiometry was within normal limit. Electronystagmography revealed the absence of spontaneous nystagmus and presence of vertical torsional nystagmus where slow-phase component directed clockwise and upward with exposure to positive pressure stimulus at the right external auditory canal. During ENG, the patient presented with feeling of oscillopsia and dizziness. Caloric test was done in both the ears which showed normal value. Cervical vestibular evoked myogenic potential (VEMP) had shown decreased thresholds. High-resolution computed tomography (HRCT) scanning of the temporal bone showed a dehiscence at the right SSC [Figure 1]. Magnetic resonance imaging of the brain was within normal limit. He was diagnosed as SSCDS and planned for surgery. The surgery was done through the repair of SSCD through transmastoid approach under local anesthesia. There was immediate postoperative resolution of pressure and sound-induced vertigo and oscillopsia, but mild unsteadiness persisted for few days. After 6 months of treatment, there was complete resolution of all the symptoms without any recurrence.
|Figure 1: High-resolution computed tomography (Poschi plane) showing the dehiscence (arrow mark) of the right superior semicircular canal|
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| Discussion|| |
SSCDS is an uncommon clinical entity. Although congenital etiology is often proposed for SSCDS, some authors believe it as due to acquired cause. Pressure from the overlying dura or temporal lobe of the brain or trauma may cause erosion of the congenitally thin bone leading to dehiscence over a period of time. This may explain why majority of cases of SSCDS seen in adult or middle age of life. The acquired causes for SSCDS are chronic otitis media with cholesteatoma, high-jugular bulb, and fibrous dysplasia. The dehiscence in SSC acts as a third window, causing pressure transmission into the labyrinth and accounting for vestibular symptoms of the patient. This third window causes dissipation of sound and increases the sensitivity of bone conduction sounds. Patients usually present with vertigo which is aggravated with intense sound, valsalva maneuvers and other maneuvers which change the intracranial pressure. Patients often present with autophony and highly sensitivity to bone-conducted sounds such as jaw movement, eye movement, and even the movement of joints in the extremities. SSCDS is often seen in middle-age group and has also seen in pediatric ages. It may be unilateral (two-third of cases) or bilateral (one-third of cases). VEMP thresholds may be decreased for both air and bone conduction in affected ear. VEMP amplitudes may be high and the responses are useful to distinguish between a conductive loss due to SSCD and ossicular fixation as VEMP response is absent or slow elevated thresholds in ossicular fixation. Cervical VEMP increases the specificity of diagnostic test for physiologic dehiscence in comparison to HRCT scan used to demonstrate the anatomical dehiscence. HRCT is considered as imaging modality for confirmation of SCD. HRCT with thin slices centered on the temporal bones with oblique coronal multiplanar reconstruction in the plane of SSC, called as the plane of Poschi, will give view of the dehiscence on the roof of SSC. Sometimes, asymptomatic false-positive findings and radiologically apparent dehiscence limit the diagnostic usefulness of HRCT. HRCT does not differentiate bone thickness <0.1 mm from true dehiscence. Normally, bone thickness over SSC is approximately 0.67 mm and standard deviation of 0.38 mm, whereas proportion of normal individuals with bony overlying of semicircular canal thickness <0.1 mm is more than the incidence of SSCD among general population (0.05%). Accordingly, the positive predictive value for HRCT in SSCD is only 57%. Along with HRCT, SSCD is confirmed by pure-tone audiometry and calorimetry. Pure-tone audiometry findings in SSCDS reveal air-bone gaps and negative bone conduction thresholds at the lower frequencies. A wrong diagnosis of ossicular fixation may be done due to air-bone gap in audiogram, which often misleads the clinician. Caloric test is usually done routinely among vertigo patients. However, the usefulness of caloric test as diagnostic test for SSCDS is questioned because SSC is not reached by caloric stimulation. The differential diagnosis of SSCDS is always considered while evaluating a patient with a conductive hearing loss with normal reflex on a tympanogram, particularly in the presence of vestibular symptoms. A HRCT of the temporal bone is helpful for the diagnosis SSCDS in doubtful cases; thus, it will avoid unnecessary middle ear/mastoid exploration and help appropriate treatment of the patient. Patients of SSCDS with mild symptoms can be managed by conservative means. Medical treatments such as salt restriction, vestibular suppressants, diuretics, vestibular rehabilitation, and avoiding stimulus are useful. Grommet placement may reduce pressure-induced symptoms but shows variable results. This condition is treated with surgery when the symptoms are severe and affect greatly to the daily life. The principle of the surgery is to block the extra window with bone wax and the operative area with muscular fascia, bone chips, or conchal cartilage. The transmastoid approach for this disease has less complication and avoids craniotomy and temporal lobe retraction. In this case, the transmastoid approach was done for plugging the SCC. This surgery is usually done under local anesthesia which identifies accurately with certainty as the patient will complain vertigo when fistula area handled. The surgical procedure should be done with caution in view of possible sensorineural hearing loss. Other than transmastoid approach, middle fossa approach has been also used to repair the superior semicircular dehiscence by plugging the canal. It is often associated with morbidity on account of the craniotomy and temporal lobe elevation. Transcanal round window reinforcement technique is also done in SSCDS where occlusion of the round window is done through transcanal approach. It reduces the sensitivity of the inner ear to sudden fluctuations in sound or pressure.
| Conclusion|| |
SSCDS is an uncommon diagnosis for causing vertigo in clinical practice. It may present with vestibular or auditory symptoms or both in clinical presentations. The diagnosis should be done on the basis of clinical findings and investigations. Asymptomatic or mild symptoms of SSCDS can be managed conservatively. Surgery like plugging of the dehiscence of SSC is usually done in case of debilitating symptoms. SSCDS should be kept in mind of clinicians during evaluating vertigo patients for accurate diagnosis and treatment.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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