PhiliPPine Journal of otolaryngology-head and neck Surgery Vol. 32 no. 2 July– december 2017 FROM THE VIEWBOX 58 PhiliPPine Journal of otolaryngology-head and neck Surgery Unilateral Horizontal Semicircular Canal Malformation Causing Recurrent Vertigo A 62-year-old man consulted for recurrent episodes of vertigo lasting from seconds to several minutes. The vertigo was variably described as spinning, lateral swaying and a feeling of being “unsure of his position in space.” These episodes were noted to have begun when the patient was still in his 20’s. Standard pure tone audiometry revealed a mild-to-moderate downsloping mixed hearing loss in the left ear. Bithermal caloric testing indicated the presence of a significant left-sided peripheral vestibular loss. Due to the fact that the vertigo episodes presented relatively early in life, the possibility of a congenital inner ear malformation was considered as a cause for his symptoms. Computerized tomographic (CT) imaging of the temporal bone was performed. This clearly showed the left horizontal semicircular canal lacking a central bony island. (Figure 1 and 2) The cochlea, superior and posterior semicircular canals, vestibular and cochlear aqueducts and ossicular chain were grossly normal. Correspondence: Dr. Nathaniel W. Yang Department of Otorhinolaryngology Ward 10, Philippine General Hospital University of the Philippines Manila Taft Avenue, Ermita, Manila 1000 Philippines Phone: (632) 526 4360 Fax: (632) 525 5444 Email: nwyang@gmx.net The author declared that this represents original material, that the manuscript has been read and approved by the author, that the requirements for authorship have been met by the author, and that the author believes that the manuscript represents honest work. Disclosures: The author signed a disclosure that there are no financial or other (including personal) relationships, intellectual passion, political or religious beliefs, and institutional affiliations that might lead to a conflict of interest. Philipp J Otolaryngol Head Neck Surg 2017; 32 (2): 58-59 c Philippine Society of Otolaryngology – Head and Neck Surgery, Inc. Nathaniel W. Yang, MD Department of Otorhinolaryngology College of Medicine – Philippine General Hospital University of the Philippines Manila Department of Otolaryngology Head and Neck Surgery Far Eastern University - Nicanor Reyes Medical Foundation Institute of Medicine Creative Commons (CC BY-NC-ND 4.0) Attribution - NonCommercial - NoDerivatives 4.0 International Figure 1. Computerized tomographic imaging of the temporal bone in the axial view at the level of the horizontal semicircular canal. The arrow points to the left horizontal semicircular canal which lacks a central bony island and has a cystic appearance. In comparison, the right horizontal semicircular canal has the classic “signet ring” appearance. PhiliPPine Journal of otolaryngology-head and neck Surgery Vol. 32 no. 2 July– december 2017 PhiliPPine Journal of otolaryngology-head and neck Surgery 59 FROM THE VIEWBOX REFERENCES Johnson J, Lalwani AK. Sensorineural and conductive hearing loss associated with 1. lateral semicircular canal malformation. Laryngoscope 2000 Oct;110(10):1673–1679. DOI:10.1097/00005537-200010000-00019 PMID: 11037823 Casselman JW, Delanote J, Kuhweide R, van Dinther J, De Foer B, Offeciers EF. Congenital 2. malformations of the temporal bone. In: Lemmerling M, De Foer B, editors. Temporal bone imaging. Berlin Heidelberg: Springer-Verlag; 2015, pp. 120-154. Kim CH, Shin JE, Lee YJ, Park HJ. Clinical characteristics of 7 patients with lateral semicircular 3. canal dysplasia. Res Vestib Sci 2012;11(2):64-68. A malformation of the horizontal or lateral semicircular canal is one of the most common inner ear malformations since it is the last vestibular structure to be formed during inner ear embryogenesis. As such, it may occur in isolation or may be associated with other vestibular, cochlear, or middle ear malformations.1,2 Although vertigo and dizziness are symptoms to be expected in such a condition, existing data indicates that it may be totally asymptomatic or it may also present as a sensorineural, conductive or mixed type of hearing loss.1,3 Radiologic imaging is of prime importance in diagnosing such Figure 2. Computerized tomographic imaging of the temporal bone in the coronal view showing the horizontal semicircular canals at two different levels. A. is at the level of the ampullated end of the canal, where the canals look similar (white arrows). B. is at the midpoint of the canal where the right side shows a small ovoid lumen separated from the vestibule by bone; whereas the left side shows an enlarged lumen representing the combined vestibule and semicircular canal without any intervening bone (angled white arrows). These images illustrate the difficulty in identifying the abnormality on coronal view as compared to the axial view. conditions especially when auditory and/or vestibular symptoms manifest early in life. This case perfectly illustrates the need for such studies as the patient went undiagnosed for more than forty years! No definitive statements can be gleaned from existing medical literature with respect to treatment. However, in patients with debilitating vestibular symptoms, management with modalities that selectively target the vestibular system, but spare the auditory system, such as vestibular neurectomy and trans-tympanic aminoglycoside therapy appear to be reasonable options.