SCDS is a rare but quite distinct (and fascinating) condition. It is characterized by abnormal thinning or loss of a small area of skull bone that covers the superior semicircular canal of the inner, resulting in abnormal transmission of sound and pressure to this canal.

Symptoms of SCDS include:

  • Pulsatile tinnitus
    • due to hearing the sound of one’s own heart beat in the affected ear
  • Vertigo and nystagmus triggered by certain sounds
  • Vertigo and nystagmus triggered by straining (e.g. coughing, blowing one’s nose)
  • Increased sensitivity to self-generated noises. Different descriptions of this phenomenon include:
    • finding their breathing is too loud
    • hearing their eyes move
    • hearing their footsteps
    • hearing their joints creak
    • finding their own voices are too loud and are distorted
  • Increased sensitivity to noises
  • Low frequency conductive hearing loss

Diagnosis

Tests like audiograms, vestibular evoked myogenic potentials (VEMPs), electrocochleography, and video-nystagmography (VNG) can provide vital clues about SCDS.

A temporal bone CT scan (not an MRI or a general head CT) is the best test to identify the thinning or loss of the temporal bone overlying the superior semicircular canal.

Treatment

If the symptoms affect a patient’s life significantly, surgical repair of the dehiscence can be performed. Surgical approaches include transmastoid (i.e. through the mastoid bone) or middle fossa craniotomy. The best approach should be discussed with a neuro-otologist.