Superior canal dehiscence
Definition & Facts
Dr. Lloyd Minor, MD of Johns Hopkins University originally described superior canal dehiscence in 1998. SCD is a hole in or thinning of the temporal bone in the ear. It affects one to two percent of the population, usually adults in their 30’s and 40’s, with men and women being equally susceptible.
Not all patients experience all the symptoms and many patients are treated for other conditions before the correct diagnosis is reached, usually by an audiologist or an otolaryngologist, also known as an ear, nose, and throat doctor or ENT.
Symptoms & Complaints
Vestibular symptoms include the following:
- Chronic unsteadiness.
- Tullio phenomenon: this is vertigo and involuntary eye movement brought on by loud sounds.
- Hennebert's sign: this is vertigo and involuntary eye movement brought on by pressure, such as in the cabin of an airliner.
- Oscillopsia: this is a vision problem where objects in the visual field appear to oscillate. It can be brought on by either loud sounds and/or pressure.
- Brain fog.
- Headaches or migraines.
Auditory symptoms include the following:
- Pulsatile tinnitus: this is a noise in the ear that is experienced like a rhythmic pulsing that oftentimes corresponds with the heartbeat. It can sound like a thumping or whooshing sound.
- Hearing loss
- Conductive hyperacusis: this is an increased sensitivity to sounds that are conducted to the ears through the bones.
- Autophony: this often sounds like an echo from eating or talking.
- Aural fullness: this is the feeling of pressure or fullness in the ears.
The cause for SCSD is not conclusively known at this time, but genetic factors are likely at play. In many cases, it is thought that the superior semicircular canal is about 37 percent thinner than normal among those with this disorder. This makes that bone more susceptible to damage through physical traumatic head injury and erosion from aging.
Another theory is that patients with an already thin bone may damage it through increased intracranial pressure resulting from straining, sneezing, or coughing. It is also believed that some infectious diseases may cause SCD.
Diagnosis & Tests
There are many tests used to diagnose superior canal dehiscence. An ENT may order several diagnostic tests, which may include:
- Vestibular evoked myogenic potential or VEMP test: This measures the reflex in the neck muscle that responds to sound. An electrode is placed on your neck, and then you will be given a low to mid-range tone in one ear at a time. The sound may cause that muscle to muscle to react abnormally indicating a problem.
- Videonystagmography or VNG: This measures eye movement by placing small electrodes around the eye. The goal is to see if one or both eyes have abnormal movement while introducing various stimuli such as changed temperature in the ear canal by using water or air.
- Electrocochleography or ECOG: This measures the electrical signals generated in the inner ear as a result to sound stimulation.
- Rotational chair test: This test measures eye movement while you slowly turn in a motorized chair.
- Pure tone audiometry: measures the volume and tones you can hear in each ear.
- Computed tomography (CT) scan: If SCD is suspected for a patient, a coronal CT scan will be used to confirm the diagnosis. Through this scan, an ENT should be able to see if a hole is present in the temporal bone.
Treatment & Therapy
Treatment for superior canal dehiscence is dependent on the severity of the symptoms. In minor cases, patients may be able to avoid the triggers such as loud noises and changes in pressure or altitude. In these cases, genetic counseling may be in order to help determine the triggers and how to avoid them.
For patients with severe symptoms that are becoming debilitating to normal life functions, surgical intervention may be recommended. There are currently two approaches to surgical intervention:
- Middle fossa craniotomy: In this approach, a doctor will take a small section of the skull out to plug the hole in the temporal bone.
- Transmastoid Repair: This approach comes in from behind the ear through the mastoid process. Like the middle fossa craniotomy, the transmastoid approach aims to plug the hole in the temporal bone. Some studies have shown this approach is less risky for some patients, though the doctor never actually sees the SCD hole.
For patients with hearing loss, either with or without surgical intervention, hearing aids may be needed to help relieve the associated hearing loss. Consultation with a qualified audiologist will help with selecting the best device.
Prevention & Prophylaxis
However, for those patients with thinner temporal bones, who may be more susceptible to damage to the bone, extra care can be prevent the damage to the bone that will ultimate cause the symptoms associated with SCD. This includes wearing a helmet with participating in activities like bike riding, skating, skiing, or any other activity that may result in closed head injuries.
Further, paying close attention to symptoms before they become severe may help identify the syndrome early and increase the success of treatment.