Definition and Overview
Superior canal dehiscence syndrome (SCDS) is a vestibular disease caused by a defect in the temporal bone that covers the superior semicircular canal of the inner ear. It was first reported in 1998, and the representative symptoms include the Tullio phenomenon, which causes dizziness due to loud sounds or pressure changes, and autophony, where one's own voice is heard loudly.
The ICD-10 code applies H83.8 (other specified diseases of the inner ear).
pathophysiology
The normal inner ear processes external acoustic energy and pressure through two windows: the oval window and the round window. When the bone covering the superior semicircular canal is defective, this area acts as a third window. Sound and pressure energy deviates from the normal path and leaks into the superior semicircular canal, stimulating the vestibular system abnormally, resulting in dizziness caused by sound and pressure.
symptoms
Symptoms of Superior semicircular canal dehiscence syndrome appear when acoustic and pressure energy is transmitted to the defect area.
Main symptoms:
- Dizziness caused by loud noises (Tulio phenomenon)
- Dizziness caused by changes in pressure, such as blowing your nose or lifting heavy objects
- Self-Hearing: Hearing your own voice, footsteps, or heartbeat loudly.
- Pulsatile tinnitus
- Hearing changes in the pattern of conductive hearing loss
- Disorders of balance and chronic instability
diagnosis
High-resolution temporal bone CT
This is a key test that directly identifies defects in the bone covering the superior semicircular canal. The location and size of the defect are evaluated, and reconstructed images aligned to the superior semicircular canal plane are used to reduce false positives.
Cervical vestibular evoked muscle potential (VEMP)
The vestibular evoked myogenic potential (VEMP) test is characterized by a decrease in stimulation threshold and an increase in response amplitude. This is because the third window effect increases the acoustic sensitivity of the vestibular system.
hearing test
Patterns of conductive hearing loss may be observed, and bone conduction thresholds may be measured lower than normal. Differentiation from middle ear disease is necessary.
Differential diagnosis
- Meniere's disease: Recurrent rotational vertigo with hearing fluctuations and tinnitus.
- Benign paroxysmal positional vertigo (BPPV): Rotational dizziness lasting a few seconds that occurs when the head changes position.
- Patent Eustachian tube: Causes autophony, but does not cause dizziness caused by sound or pressure.
- Perilymph fistula: Dizziness occurs due to pressure changes, so differentiation is required.
treatment
progress observation
If symptoms are mild and do not interfere with daily life, follow-up is given priority. Teach children to avoid symptom triggers such as loud noises, blowing their nose, and lifting heavy objects.
surgical closure
If dizziness or self-healing is severe and daily life is difficult, consider surgery to close the defect. The third window effect is blocked by covering or blocking the defect using the middle cranial or transmandibular approach. Improvement of dizziness and self-stiffness symptoms was reported after surgery.
Clinical implications
The diagnosis of Superior semicircular canal dehiscence syndrome is increasing due to advances in imaging and testing technology, but not all patients show symptoms even if defects are seen on temporal bone CT. Diagnosis should be made by combining imaging findings, clinical symptoms, and VEMP results, and unnecessary surgery for asymptomatic defects should be avoided.