What would your reaction be if a patient stated they heard their eyeball move? They might also report that they get dizzy when loud sounds occur (Tullio phenomenon) and when they move their head quickly from one side to the other. They could also report aural fullness, autophony (echo or reverberation of the ear when speaking chewing or swallowing, hearing ones own heart beat) and maybe even some hearing loss. This cluster of symptoms is quite puzzling and frustrating for the affected person and the diagnosis can be difficult.
In 1998, Dr. Lloyd Minor, a physician from Johns Hopkins, described superior canal dehiscence syndrome (SCDS or SCD) which can cause hearing difficulties, balance issues, or both. The cause is due to an opening in the bone overlying one of the inner ear balance canals due to congenital defect, trauma or infection.
Audiometrically, a low to mid-frequency (250-1,000 Hz) conductive hearing loss can be present, but with no supporting evidence of middle ear involvement. The conductive loss associated with SCDS not only shows air/bone gaps at these frequencies but also a hypersensitivity of bone conduction thresholds– as low as -5dB HL at 250-500 with decreasing sensitivity as the frequency increases. The thinning or absence of the bone on the superior canal creates an additional window in the inner ear, along with the round and oval windows. This “third window” allows for air conductive (AC) sound energy to be diverted away from the cochlea, decreasing the pressure between the scala vestibuli and scala tympani. The “third window” will not depress bone conductive (BC) thresholds, but will enhance them.
Superior Canal Dehiscence Syndrome Often Misdiagnosed
This condition is easily misdiagnosed as it can masquerade as several conditions such as Eustachian tube dysfunction, patulous Eustachian tube, Benighn proxysmal positional verigo (BPPV), Meniere’s disease, Vestibular Neuronitis/neuritis, Perilymph fistula and Labyrinthitis.
The diagnosis can be confirmed with high resolution CT scans of the temporal bone, reformatted to the planes parallel and perpendicular to the superior canals. In the world of radiology these are called the Poeschel and Stenver planes. As you look at this scan, you will see the Superior Canal on the left, the bone is not connecting on the top portion as it should be.
Depending on how SCDS is affecting the quality of life for the affected person, treatments include: hearing aid for the affected side, avoidance of loud sounds; surgery (middle fossa craniotomy, transmastoid repair). Surgical risks include hearing loss (12% of cases) and reoccurring SCDS.