Superior semicircular canal dehiscence syndrome
Superior semicircular canal dehiscence syndrome (SCDS) is a recently described inner ear abnormality, where a clinical disequilibrium phenomenon is associated with the absence of the bony covering of the superior semicircular canal (SSC).
Notably, this CT finding has also been described in ~10% of individuals without these clinical features 1. Current literature suggests that the term SCDS should be reserved for patients who have both the clinical and radiological features.
The incidence of superior semicircular canal dehiscence syndrome increases with age.
Patients may experience vestibular and visual symptoms. The classic presentation is Tullio phenomenon: vertigo and nystagmus induced by loud noises. The same symptoms may be brought on by sudden changes in pressure, e.g. Valsalva manoeuvre. In some, there is a history of longstanding disequilibrium and unsteadiness 1. It can also present with a conductive hearing loss that mimics otosclerosis and could explain some cases of persistent conductive hearing loss after uneventful stapedectomy 7. Some patients experience oscillopsia 11.
Dehiscence of the SSC forms a "third window" into the inner ear, in addition to the round and oval windows. This allows motion of the endolymph to be induced by sound and pressure stimuli 2.
Thin slice petrous temporal bone CT demonstrates a defect in the arcuate eminence (bony covering) of the SSC, best seen in the coronal plane. Reducing the slice thickness from 1 mm to 0.5 mm may improve detection rates from 50 to 93% 2.
MRI is not usually required for the initial diagnosis of SCDS, but there is research showing it may be as good and possibly better than CT. Broweays et al. 10 in 2013 found that MRI in 112 patients had a sensitivity of 100%, specificity of 96.5%, positive predictive value of 61.1%, and negative predictive value was 100% compared to CT thereby making it an excellent 'rule out' test. This said, however, most surgeons would be reluctant to operate without a CT, as it is far superior in defining the bony anatomy.
MRI is more often currently used to follow up patients that have had surgery, allowing assessment of the integrity of the bony covering of the SSC. A thin volumetric T2 SPACE is the best sequence.
Treatment and prognosis
Surgical procedures are performed through a middle cranial fossa approach. Plugging or resurfacing the superior semicircular canal has been documented to resolve or improve the symptoms 4. Canal plugging is thought to achieve long-term control more often than resurfacing 6.
History and etymology
It was initially described by L B Minor et al. in 2005 6.
Inner ear pathology
inner ear anatomy
- enlarged vestibular aqueduct
- semicircular canal dysplasia
- classification of cochlear anomalies
- infection and inflammation
- trauma and miscellaneous
- 1. Williamson RA, Vrabec JT, Coker NJ et-al. Coronal computed tomography prevalence of superior semicircular canal dehiscence. Otolaryngol Head Neck Surg. 2003;129 (5): 481-9. Otolaryngol Head Neck Surg (link) - Pubmed citation
- 2. Belden CJ, Weg N, Minor LB et-al. CT evaluation of bone dehiscence of the superior semicircular canal as a cause of sound- and/or pressure-induced vertigo. Radiology. 2003;226 (2): 337-43. doi:10.1148/radiol.2262010897 - Pubmed citation
- 3. Curtin HD. Superior semicircular canal dehiscence syndrome and multi-detector row CT. Radiology. 2003;226 (2): 312-4. doi:10.1148/radiol.2262021327 - Pubmed citation
- 4. Brantberg K, Bergenius J, Mendel L et-al. Symptoms, findings and treatment in patients with dehiscence of the superior semicircular canal. Acta Otolaryngol. 2001;121 (1): 68-75. - Pubmed citation
- 5. Merchant SN, Rosowski JJ, McKenna MJ. Superior semicircular canal dehiscence mimicking otosclerotic hearing loss. Adv. Otorhinolaryngol. 2007;65: 137-45. doi:10.1159/000098790 - Free text at pubmed - Pubmed citation
- 6. Minor LB. Clinical manifestations of superior semicircular canal dehiscence. Laryngoscope. 2005;115 (10): 1717-27. doi:10.1097/01.mlg.0000178324.55729.b7 - Pubmed citation
- 7. Mikulec AA, McKenna MJ, Ramsey MJ et-al. Superior semicircular canal dehiscence presenting as conductive hearing loss without vertigo. Otol. Neurotol. 2004;25 (2): 121-9. Pubmed citation
- 8. Banerjee A, Whyte A, Atlas MD. Superior canal dehiscence: review of a new condition. Clin Otolaryngol. 2005;30 (1): 9-15. doi:10.1111/j.1365-2273.2004.00940.x - Pubmed citation
- 9. Nadgir RN, Ozonoff A, Devaiah AK et-al. Superior semicircular canal dehiscence: congenital or acquired condition?. AJNR Am J Neuroradiol. 2011;32 (5): 947-9. doi:10.3174/ajnr.A2437 - Pubmed citation
- 10. Browaeys P, Larson TL, Wong ML et-al. Can MRI replace CT in evaluating semicircular canal dehiscence?. AJNR Am J Neuroradiol. 2013;34 (7): 1421-7. doi:10.3174/ajnr.A3459 - Pubmed citation
- 11. Yew A, Zarinkhou G, Spasic M et-al. Characteristics and management of superior semicircular canal dehiscence. J Neurol Surg B Skull Base. 2012;73 (06): 365-70. doi:10.1055/s-0032-1324397 - Free text at pubmed - Pubmed citation