Superior Semicircular Canal Dehiscence Syndrome (SSCD) is a disease that has been recognized very recently compared to other diseases that are among the diseases that cause hearing loss and dizziness. The disease was first described by Minor et al. in 1998.
Because of the bony defect located on the superior semicircular canal, these patients have a "third hole" other than the oval window and the round window. This hole is in contact with the scala vestibuli. Acoustic energy transmitted to the oval window via the ossicular chain prefers the lower impedance scala vestibuli direction and the third window rather than the higher impedance scala tympani direction.
While dizziness occurs due to abnormally stimulated superior semicircular canal, airway thresholds decrease due to low acoustic energy reaching the basement membrane. However, since the bone conduction thresholds increase due to dehiscence in the superior semicircular canal, the thresholds between the airway and the bone conduction increase, and this causes a false conductive hearing loss. Because the pressure changes in the middle ear due to the “third window”are easily reflected in the inner ear, these also trigger dizziness.
It is accepted that the bone over the superior semicircular canal becomes thinner and symptoms begin with increased intracranial pressure. Its frequency is around 0.5%.
While patients primarily complain of dizziness, body sounds (respiration, circulation, joint movements, eye movements), or the person's own voice may cause significant discomfort (hyperacusis) due to the third window.
The etiology of the disease is not fully known. There are studies showing that there is a developmental, congenital, and also genetic background. Vestibular symptoms (Tullio's phenomenon and Hennebert's sign) and torsional nystagmus are seen in most patients, triggered by pressure or noise. Hyperacusis or autophonia may develop. High-resolution computed tomography with thin sections is used for diagnosis. Demonstration of dehiscence in the reconstructed sections (Pöschl plane) parallel to the long axis of the SSC is diagnostic. In addition, Vestibular Evoked Myogenic Potentials (VEMP) are very useful in the diagnosis and follow-up of SSCD. Extremely high VEMP responses are seen at low stimulus intensities in patients with SSCD. The sensitivity of the VEMP study in the diagnosis of SSCD is between 80-100%; Its specificity is between 90-100%. It is stated that the sensitivity of the VEMP test performed with tone burst stimulus is over 90% at all ages.
In mild cases, there is no need for treatment, but only the prevention of factors that cause pressure increase is sufficient. However, in patients with severe symptoms, surgical closure of the third window is recommended. The mid-cranial cavity approach or the transmastoid approach is used in surgery.
