What is Superior Canal Dehiscence?
Superior canal dehiscence (SCD) occurs when there is an opening (dehiscence) in the bone above the superior semicircular canal of the inner ear due to progressive deterioration or due to a head trauma resulting in sensations of vertigo, tinnitus (persistent ringing sounds), and unusual sensitivity to sounds. To understand how these sensations develop, it is important to have knowledge of the anatomy and physiology of the ear.
Anatomy & Physiology of the Ear
The ear consists of 3 parts: external ear, middle ear, and inner ear. The external ear conducts the sound and leads it to the middle ear. The middle ear is connected to the nose and to the inner ear. Pressure is equalized in the middle ear with its connection to the nose, through a canal known as the Eustachian tube. The sound is conducted into the inner ear through the oval window that then transmits the vibration through nerve impulses to the brain. These nerve impulses communicate with the brain, which makes us hear sound. The inner ear has a coiled structure called the cochlea that transmits the sound vibrations and 3 semicircular canals (part of the vestibular labyrinth) that help to maintain balance during head rotations. Pressure changes due to sound vibrations are balanced with the help of the opening of the oval window and the round window where the sound vibrations exit from the inner ear.
In 1998, Lloyd B. Minor and colleagues noticed patients who had balance and sound processing issues with eye movements in the region of the superior semicircular canal in reaction to certain stimuli. In this condition, the opening of the bone causes a third window through which pressure changes are directed. As a result of this extra opening, imbalance and irregularities in sound are experienced
What are the Causes of Superior Canal Dehiscence?
It is not very clear how SCD develops. The condition is most often observed in adults with no gender bias. However, when seen in children, it is often accompanied by hearing issues rather than problems with balance. There are a few causes, which are listed below:
- Congenital Abnormality: Birth defects are one of the primary factors, which results in thinning of the bone above the semicircular canal
- CSF Pressure: Increase in cerebrospinal fluid (CSF) pressure causes damage to the bone
- Trauma: Mild trauma to the brain sustained during diving or contact sports can cause damage to the bone
- Fractures: Fracturing of the bone may occur as a result of trauma to the head
- Age: Age is a significant factor, as with increasing age, the bone becomes thinner
- Alberti PW. The Anatomy and Physiology of the Ear and Hearing. - (https://www.who.int/occupational_health/publications/noise2.pdf)
- UTHealth. Otorhinolaryngology – Head & Neck Surgery. Updated 2019; Accessed Apr 27, 2019; Cited Apr 27, 2019. - (https://med.uth.edu/orl/online-ear-disease-photo-book/chapter-3-ear-anatomy/ear-anatomy-inner-ear/)
- Ward BK, Carey JP, Minor LB. Superior Canal Dehiscence Syndrome: Lessons from the First 20 Years. Front Neurol. 2017; 8: 177.
- Diaz MP, Lesser JCC, Alarcón AV. Superior Semicircular Canal Dehiscence Syndrome - Diagnosis and Surgical Management. Int Arch Otorhinolaryngol. 2017; 21(2):195-8. - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5375705/)
- Bance M. Superior Semicircular Canal Dehiscence. Can Audiol. 2014; Vol.1 (4).
- Peng KA, Ahmed S, Yang I, Gopen Q. Temporal Bone Fracture Causing Superior Semicircular Canal Dehiscence. Case Rep Otolaryngol. Vol. 2014, Article ID 817291.
- Minor LB. Superior Semicircular Canal Dehiscence (SSCD). Accessed Apr. 27, 2019. Cited Apr 27, 2019. - (https://vestibular.org/superior-canal-dehiscence-scd)
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