Superior Canal Dehiscence Syndrome (SCDS) is a relatively recently discovered syndrome involving an abnormality of the inner ear that can be responsible for a number of bothersome symptoms. It was first described by Dr. Lloyd Minor at Johns Hopkins University. SCDS is a developmental condition where the bone that separates the inner ear from the brain basically “gives way”, and an unnatural opening between the two is created. There is belief that some people are born with an unusually thin bony plate at this area, and events such as head trauma, coughing, sneezing or physical strain can create the opening.
Once this opening exists, the fluid dynamics of the inner ear are altered. Think about how water moves in a water balloon as opposed to a water bottle. The bottle has solid edges, and the balloon has flexible edges. This is an extreme analogy, but helps make the point that in SCDS, a portion of the inner ear that was a solid edge becomes a flexible edge.
Keep in mind that the inner ears work by motion activated fluid movement, and the first thing the brain does when it gets a signal of movement from the inner ear is to immediately check with the other inner ear to see if it is registering the same movement. If the answer is “same” all is well. If the answer is “not quite the same” trouble ensues.
The opening not only changes fluid dynamics when you move, the fluid can be moved by loud sounds or pressure in the ear canals. When the eardrum responds to sound or pressure, it transmits that energy to the inner ear through fluid waves. When the fluid starts moving in the ear with the dehiscence, or opening, it causes a disruption of fluid movement in that ear. This results in an asymmetric response between the two inner ears, and the patient is likely to register that difference as dizziness or vertigo.
Because SCDS is an abnormal opening within the skull, it is very susceptible to internally generated sound and pressure. If you have ever had a stopped up ear, and noticed that your voice or your chewing seemed awfully loud, you can relate in a small way. Basically, in SCDS, there is a direct opening to the inner ear from inside the skull. As a result, sounds generated inside the skull, like your pulse, your eye movements, and most notably your voice all seem too loud in the ear affected by SCDS.
We will continue on the topic of SCDS next week. For additional information read this detailed article describing Dr. Minor performing the surgery to close the canal dehiscence.
Photo courtesy of dariuskohandmd.com