Superior semicircular canal dehiscence syndrome  is a set of hearing and balance symptoms, related to a rare medical condition of the inner ear, known as superior canal dehiscence. The symptoms are caused by a thinning or complete absence of the part of the temporal bone overlying the superior semicircular canal of the vestibular system. There is evidence that this rare defect, or susceptibility, is congenital. There are also numerous cases of symptoms arising after physical trauma to the head. It was first described in 1998 by Lloyd B. Minor of Johns Hopkins University in Baltimore. Symptoms
Superior canal dehiscence (SCD) can affect both hearing and balance to different extents in different people.Symptoms of SCDS include:

Autophony – persons own speech or other self-generated noises (e.g. heartbeat, eye movements, creaking joints, chewing) are heard unusually loudly in the affected ear
Dizziness/ vertigo/ chronic disequilibrium caused by the dysfunction of the superior semicircular canal
Tullio phenomenon – sound-induced vertigo, disequilibrium or dizziness, nystagmus and oscillopsia
Pulse-synchronous oscillopsia
Hyperacusis – the over-sensitivity to sound
Low-frequency conductive hearing loss
A feeling of fullness in the affected ear
Pulsatile tinnitus
Brain fog
Fatigue
Headache/migraine
Tinnitus – high pitched ringing in the ear

Symptoms in detail
SCDS-related autophony differs greatly in quality and range from the more common form which results from an open, or patulous Eustachian tube through which sufferers of this disorder hear the sound of their own voice and breathing. In contrast, patients with SCDS-related autophony report hearing their own voice as a disturbingly loud and distorted "kazoo-like" sound deep inside the head as if relayed through "a cracked loudspeaker."
An explanation for this erosion of the bone has not yet been found. Diagnosis
The presence of dehiscence can be detected by a high definition (0.6 mm or less) coronal CT scan of the temporal bone, currently the most reliable way to distinguish between superior canal dehiscence syndrome (SCDS) and other conditions of the inner ear involving similar symptoms such as Ménières disease, perilymphatic fistula and cochlea-facial nerve dehiscence. Other diagnostic tools include the vestibular evoked myogenic potential or VEMP test, videonystagmography (VNG), electrocochleography (ECOG) and the rotational chair test. An accurate diagnosis is of great significance as unnecessary exploratory middle ear surgery may thus be avoided. Several of the symptoms typical to SCDS (e.g. vertigo and Tullio) may also be present singly or as part of Ménières disease, sometimes causing the one illness to be confused with the other. There are reported cases of patients being affected by both Ménières disease and SCDS concurrently.As SCDS is a very rare and still a relatively unknown condition, obtaining an accurate diagnosis of this distressing (and even disabling) disease may take some time as many health care professionals are not yet aware of its existence and frequently dismiss symptoms as being mental health-related. Treatment
Once diagnosed, the gap in the temporal bone can be repaired by surgical resurfacing of the affected bone or plugging of the superior semicircular canal. These techniques are performed by accessing the site of the dehiscence either via a middle fossa craniotomy or via a canal drilled through the transmastoid bone behind the affected ear.