Abstract

Superior canal dehiscence is a disorder of the inner ear in which an abnormal opening develops in the bone overlying the superior semicircular canal. This defect creates a third mobile window into the inner ear, leading to a range of auditory and vestibular symptoms. This report describes a second case in a series, focusing on the clinical presentation, diagnostic evaluation, and successful surgical management of the condition.

Introduction

Superior canal dehiscence syndrome was first characterized in the late twentieth century. The condition occurs when the thin layer of bone covering the superior semicircular canal is absent or eroded. As a result, the inner ear becomes abnormally sensitive to pressure and sound. Patients often experience sound-induced vertigo, pressure-induced nystagmus, and persistent disequilibrium. This case report highlights a typical presentation and the steps taken to confirm the diagnosis.

Case Presentation

A middle-aged adult presented to an outpatient balance clinic with a two-year history of progressive imbalance and episodic vertigo. The patient reported that loud noises, such as a door slamming or a dog barking, triggered brief but intense episodes of spinning. In addition, the patient noted that straining, lifting heavy objects, or pressing a finger into the ear canal produced a sensation of movement. The patient denied hearing loss but described a persistent feeling of fullness in one ear. There was no history of head trauma, middle ear infection, or otologic surgery.

Examination Findings

Physical examination revealed normal tympanic membranes and intact external auditory canals. Observation of the eyes during loud sound stimulation demonstrated a brief conjugate upward and torsional nystagmus, consistent with excitation of the superior semicircular canal. Application of positive pressure to the external auditory canal with a pneumatic otoscope produced a similar eye movement. When the patient performed a Valsalva maneuver against a closed glottis, a small downward-beating nystagmus was observed. The remainder of the cranial nerve examination was unremarkable. The patient walked with a slightly cautious gait but did not require assistance.

Diagnostic Workup

Pure tone audiometry showed normal hearing thresholds bilaterally with an air-bone gap present in the lower frequencies when measured with a bone conduction transducer. Cervical vestibular evoked myogenic potentials demonstrated markedly reduced thresholds on the affected side, suggesting enhanced sacculocollic pathway sensitivity. Ocular vestibular evoked myogenic potentials were also abnormal. A high-resolution computed tomography scan of the temporal bones, obtained in the plane of the superior semicircular canal, confirmed the absence of bone over a segment of the superior canal on the symptomatic side. The imaging findings correlated closely with the physiologic test results.

Differential Diagnosis

The differential diagnosis included perilymphatic fistula, Meniere disease, otosclerosis, and benign paroxysmal positional vertigo. The combination of sound and pressure induced vertigo with characteristic nystagmus and confirmatory imaging distinguished superior canal dehiscence from these other conditions. The presence of an air-bone gap on audiometry without evidence of ossicular chain disease further supported the diagnosis.

Treatment and Outcome

Initial management was conservative, including avoidance of triggering stimuli and use of earplugs in noisy environments. However, the patient experienced persistent disequilibrium that interfered with daily activities. Surgical treatment was therefore recommended. The patient underwent a middle cranial fossa approach with resurfacing of the dehiscent superior semicircular canal. The postoperative course was uneventful. At the three month follow up, the patient reported complete resolution of sound induced vertigo and significant improvement in balance. Repeat audiometry showed closure of the low frequency air-bone gap, and cervical vestibular evoked myogenic potential thresholds returned to the normal range.

Discussion

This case illustrates the classic features of superior canal dehiscence. The diagnosis should be considered in any patient with sound or pressure induced vertigo and oscillopsia. A focused physical examination can reveal the characteristic pattern of nystagmus, and physiologic testing provides supportive evidence. Imaging with high-resolution computed tomography is the definitive diagnostic modality. Surgical repair is an effective option for patients who do not respond to conservative measures. This second case in the series reinforces the importance of a systematic approach to the evaluation of inner ear disorders that involve a third window phenomenon.

Keywords

• Superior canal dehiscence
• Superior semicircular canal dehiscence syndrome
• Third window phenomenon
• Tullio phenomenon
• Vestibular evoked myogenic potentials
• Sound induced vertigo
• Middle cranial fossa resurfacing