Superior canal dehiscence syndrome
A rare inner-ear disorder causing hearing and balance symptoms.
Superior canal dehiscence syndrome (SCDS) is a rare inner-ear disorder that causes a specific set of hearing and balance problems. It occurs when the temporal bone over the superior semicircular canal becomes thin or is completely missing. This defect may be present from birth, and symptoms can also appear after a head injury. The condition was first identified in 1998 by Lloyd B. Minor at Johns Hopkins University.
Symptoms vary from person to person and can affect both hearing and balance. A common symptom is autophony, where a person hears their own voice, heartbeat, eye movements, joint creaks, or chewing unusually loudly in the affected ear. Unlike the more common autophony from a patulous Eustachian tube, SCDS-related autophony makes one’s own voice sound disturbingly loud and distorted, like a “kazoo” or “cracked loudspeaker.” Some people can even hear a tuning fork placed on their ankle. Hearing the sound of eyeballs moving—described as “sandpaper on wood”—is a distinctive sign of SCDS.
Another key symptom is the Tullio phenomenon: sound-induced vertigo, dizziness, or loss of balance. This can be triggered by everyday noises like a plastic bag rustling, coins clinking, a ringing phone, or even the person’s own voice. It may also cause involuntary eye movements (nystagmus) that make the world seem to tilt up to 15 degrees. Changes in middle-ear pressure, such as from flying or nose-blowing, can also bring on disequilibrium or nystagmus.
Many people with SCDS have low-frequency conductive hearing loss. This happens because the bone gap acts as a “third window,” diverting sound vibrations away from the cochlea and into the intracranial space. The hearing loss is more severe at low frequencies and can be mistaken for otosclerosis. Some patients actually have enhanced low-frequency hearing through bone conduction, which is why they can hear a tuning fork on their ankle.
Pulsatile tinnitus is another typical symptom. The bone gap lets normal pulse-related pressure changes from the cranial cavity enter the inner ear, creating a “swooshing” sound or a cricket-like chirrup that pulses with the heartbeat.
Brain fog and fatigue are common because the brain must work unusually hard to maintain balance while receiving confusing signals from the faulty canal. Headache and migraine often occur as the body overcompensates for poor hearing by tensing muscles in t
- first described
- 1998
- discoverer
- Lloyd B. Minor
- institution
- Johns Hopkins University
- affected population
- approximately 2.5% of the general population have bone thickness of 60–70% of normal
- normal bone thickness
- 0.8 mm
- typical dehiscent bone thickness
- 0.5 mm
- diagnostic imaging
- high definition (0.6 mm or less) coronal CT scan
Lore & Background
Superior canal dehiscence syndrome was first described in 1998 by Lloyd B. Minor of Johns Hopkins University in Baltimore. The condition involves a thinning or complete absence of the temporal bone overlying the superior semicircular canal. Evidence suggests this defect, or susceptibility, is congenital, though symptoms can also arise after physical head trauma. The syndrome affects both hearing and balance to varying degrees in different people.
Reader's Guide
Superior canal dehiscence syndrome is significant as a rare neurotological disorder that can cause disabling symptoms including autophony, Tullio phenomenon, hyperacusis, low-frequency conductive hearing loss, and pulsatile tinnitus. Diagnosis relies on high-definition CT scans and tests such as VEMP and videonystagmography. Treatment involves surgical resurfacing or plugging of the superior semicircular canal, accessed via middle fossa craniotomy or transmastoid approach. The condition is often underdiagnosed due to lack of awareness among healthcare professionals, and its symptoms may be mistaken for Ménière's disease or mental health issues.
Did You Know?
- The condition was first described in 1998 by Lloyd B. Minor of Johns Hopkins University.
- Approximately 2.5% of the general population have temporal bone thickness of only 60–70% of normal, predisposing them to dehiscence.
- A distinctive symptom is hearing the sound of one's own eyeballs moving, described as 'like sandpaper on wood'.
- The syndrome is sometimes called Minor's syndrome, but that eponym also refers to an unrelated spinal injury condition.
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