Learning Objectives:
Introduction: Semicircular canal dehiscence syndrome (SCDS) is caused by a bony defect of the superior semicircular canal, resulting in autophony, bone conduction of bodily sounds and pseudo conductive hearing loss. Vestibular manifestations include sound or pressure evoked vertigo. Occluding the dehiscent canal was originally described via the middle cranial fossa approach however, an alternative transmastoid approach has been used to avoid the morbidity associated with the former. The aim of this project was to determine clinical and audiological outcomes for those undergoing the transmastoid approach.
Methods: All patients suggestive of SCDS underwent CT scanning, cVEMP testing. All those with positive findings for both (dehiscent superior canal and cVEMP thresholds >35%) underwent surgery. Audiometric data were obtained and patients were sent questionnaires retrospectively regarding their symptoms.
Results: Twenty patients, with 22 affected ears underwent surgical occlusion. The commonest reported symptoms pre-operatively were hearing internal sounds, tinnitus, and fullness sensation (95%, 95%, and 82% respectively.) The symptoms most likely to show partial or complete improvement post operatively were hearing internal sounds, vertigo to loud sounds and imbalance (91%, 88% and 87% respectively.) Symptom deterioration occurred in two ears with respect to fullness. 9 patients developed new symptoms post operatively (of ‘mild nature’), the most common being imbalance (3) and fullness (2). Overall, 15 ears (68%) showed partial or complete symptom improvement, 6 showed no change and 1 was worse. The mean Dizziness Handicap Inventory Scores improved from 43 pre-op to 24 post op (p = 0.001). The mean air conduction (Fletcher's index) improved from 13.2 dB to 11.1 dB.
Conclusion: The transmastoid approach to the superior canal appears to be well tolerated and is associated with low risk to hearing. Symptom improvement is seen in two thirds, but temporary imbalance post op is common.
