Superior canal dehiscence syndrome
Encyclopedia
Superior canal dehiscence syndrome (SCDS) is a rare medical condition of the inner ear
, first described in 1998 by Dr. Lloyd B. Minor
of Johns Hopkins University, Baltimore, USA, leading to hearing and balance disorders in those affected.
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
. This may result from slow erosion of the bone or physical trauma to the skull and there is evidence that the defect or susceptibility is congenital.
(SCD) can affect both hearing and balance, to different extents in different people.
Symptoms of SCDS include:
, normally 0.8 mm thick, shows a thickness of only 0.5 mm, making it more fragile and susceptible to damage through physical head trauma or from slow erosion. An explanation for this erosion of the bone has not yet been found.
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 Ménière's disease
and perilymphatic fistula. 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 Ménière's disease, sometimes causing the one illness to be confused with the other. There are reported cases of patients being affected by both Ménière's 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.
or via a canal drilled through the transmastoid bone behind the affected ear.
. However, it is important that this disease is not confused with the paralysis and anaesthesia following a spinal injury, also known as Minor's syndrome after the Russian neurologist, Lazar Salomowitch Minor (1855–1942). In the latter case this term is now nearly obsolete.
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
, first described in 1998 by Dr. Lloyd B. Minor
Lloyd B. Minor
Lloyd Brooks Minor is an American scientist, surgeon, and provost and senior vice president for academic affairs of The Johns Hopkins University.-Biography:Minor graduated from Brown University with a Sc.B. in 1979 and an M.D. in 1982...
of Johns Hopkins University, Baltimore, USA, leading to hearing and balance disorders in those affected.
The symptoms are caused by a thinning or complete absence of the part of the temporal bone
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...
overlying the superior semicircular canal
Superior semicircular canal
The superior semicircular canal is a part of the vestibular system and detects rotation of the head around a rostral-caudal axis.-Structure:...
of the vestibular system
Vestibular system
The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...
. This may result from slow erosion of the bone or physical trauma to the skull and there is evidence that the defect or susceptibility is congenital.
Symptoms
Superior canal dehiscenceDehiscence
Dehiscence can refer to:*Dehiscence is the spontaneous opening at maturity of a plant structure, such as a fruit, anther, or sporangium, to release its contents.*Wound dehiscence is a previously closed wound reopening....
(SCD) can affect both hearing and balance, to different extents in different people.
Symptoms of SCDS include:
- AutophonyAutophonyAutophony is the unusually loud hearing of a person's own voice, breathing or other self-generated sounds.Possible causes:* The "Occlusion effect", caused by an object, such as an unvented hearing aid or a plug of ear wax, blocking the ear canal and reflecting sound vibration back towards the...
- person's own speech or other self-generated noises (e.g. heartbeat, eye movements, creaking joints, chewing) are heard unusually loudly in the affected ear - DizzinessDizzinessDizziness refers to an impairment in spatial perception and stability. The term is somewhat imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness....
/ vertigoVertigo (medical)Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear...
/ chronic disequilibriumEquilibrioceptionEquilibrioception or sense of balance is one of the physiological senses. It helps prevent humans and animals from falling over when walking or standing still. Balance is the result of a number of body systems working together: the eyes , ears and the body's sense of where it is in space ideally...
caused by the dysfunction of the superior semicircular canalSuperior semicircular canalThe superior semicircular canal is a part of the vestibular system and detects rotation of the head around a rostral-caudal axis.-Structure:... - Tullio phenomenonTullio phenomenonTullio phenomenon, sound-induced vertigo, dizziness, nausea or eye movement was first described in 1929 by the Italian biologist Prof. Pietro Tullio...
- sound-induced vertigo, disequilibrium or dizziness, nystagmus and oscillopsiaOscillopsiaOscillopsia is a visual disturbance in which objects in the visual field appear to oscillate. The severity of the effect may range from a mild blurring to rapid and periodic jumping... - Pulse-synchronous oscillopsiaOscillopsiaOscillopsia is a visual disturbance in which objects in the visual field appear to oscillate. The severity of the effect may range from a mild blurring to rapid and periodic jumping...
- HyperacusisHyperacusisHyperacusis is a health condition characterized by an over-sensitivity to certain frequency ranges of sound...
- the over-sensitivity to sound - Low-frequency conductive hearing lossConductive hearing lossConductive hearing loss occurs when there is a problem conducting sound waves anywhere along the route through the outer ear, tympanic membrane , or middle ear ....
- A feeling of fullness in the affected ear
- Pulsatile tinnitusTinnitusTinnitus |ringing]]") is the perception of sound within the human ear in the absence of corresponding external sound.Tinnitus is not a disease, but a symptom that can result from a wide range of underlying causes: abnormally loud sounds in the ear canal for even the briefest period , ear...
- Brain fogBrain fogCognitive dysfunction is defined as unusually poor mental function, associated with confusion, forgetfulness and difficulty concentrating...
- Fatigue
- HeadacheHeadacheA headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
/migraineMigraineMigraine is a chronic neurological disorder characterized by moderate to severe headaches, and nausea...
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 tubePatulous Eustachian tubePatulous Eustachian tube, also known as patent Eustachian tube, is the name of a rare physical disorder where the Eustachian tube, which is normally closed, instead stays intermittently open. When this occurs, the patient experiences autophony, the hearing of self-generated sounds...
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." Additionally they may hear the creaking and cracking of joints, the sound of their footsteps when walking or running, their heartbeat and the sound of chewing and other digestive noises. Some sufferers of this condition experience such a high level of hyperacusisHyperacusisHyperacusis is a health condition characterized by an over-sensitivity to certain frequency ranges of sound...
that a tuning fork placed on the ankle will be heard in the affected ear. The bizarre phenomenon of being able to hear the sound of the eyeballs moving in their sockets (e.g. when reading in a quiet room) "like sandpaper on wood" is one of the more distinctive features of this condition and is almost exclusively associated with SCDS.
- Tullio phenomenon, another of the more identifiable symptoms leading to a positive SCD diagnosis is sound-induced loss of balance. Patients showing this symptom may experience a loss of equilibrium, a feeling of motion sickness or even actual nausea, triggered by normal everyday sounds. Although this is often associated with loud noises, volume is not necessarily a factor. Patients describe a wide range of sounds that affect balance: the 'rattle' of a plastic bag; a cashier tossing coins into the register; a telephone ringing; a knock at the door; music; the sound of children playing and even the patient's own voice are typical examples of sounds that can cause a loss of balance when this condition is present, although there are countless others. The presence of Tullio may also mean that involuntary eye movements (nystagmus), sometimes rotational, are set off by sound, giving the sufferer the impression that the world is tipping, clockwise or anticlockwise, depending on the site of the dehiscence. Some patients report this tilt as being as much as 15°. For such persons, a visit to the concert hall or to a noisy playground may seem like being at the epicenter of an earthquake. A change of pressure within the middle ear (for example when flying or nose-blowing) may equally set off a bout of disequilibrium or nystagmus.
- Low-frequency conductive hearing loss is present in many patients with SCDS and is explained by the dehiscence acting as a "third window." Vibrations entering the ear canalEar canalThe ear canal , is a tube running from the outer ear to the middle ear. The human ear canal extends from the pinna to the eardrum and is about 35 mm in length and 5 to 10 mm in diameter....
and middle earMiddle earThe middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
are then abnormally diverted through the superior semicircular canalSuperior semicircular canalThe superior semicircular canal is a part of the vestibular system and detects rotation of the head around a rostral-caudal axis.-Structure:...
and up into the intracranial space where they become absorbed instead of being registered as sound in the hearing center, the cochleaCochleaThe cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
. Due to the difference in resistance between the normal round windowRound windowThe round window is one of the two openings into the inner ear. It is closed off from the middle ear by the round window membrane, which vibrates with opposite phase to vibrations entering the inner ear through the oval window...
and the pathological dehiscence window this hearing loss is more serious in the lower frequencies and may initially be mistaken for otosclerosisOtosclerosisOtosclerosis is an abnormal growth of bone near the middle ear. It can result in hearing loss.-Clinical description:Otosclerosis can result in conductive and/or sensorineural hearing loss...
. In some patients there is true enhancement of low frequency hearing via bone conducted sound. A clinical sign of this phenomenon is the ability of the patient to hear (not feel) a tuning fork placed upon the ankle bone.
- Pulsatile tinnitus is yet another of the typical symptoms of SCDS and is caused by the gap in the dehiscent bone allowing the normal pulse-related pressure changes within the cranial cavity to enter the inner ear abnormally. This pressure change thus becomes audible and an existing tinnitus will be perceived as containing a pulse-synchronized "wave" or "blip" which patients describe as a "swooshing" sound or as being like the chirrup of a cricket or grasshopper.
- Brain fog and fatigue are both common SCDS symptoms and are caused by the brain having to spend an unusual amount of its energy on the simple act of keeping the body in a state of equilibrium when it is constantly receiving confusing signals from the dysfunctional semicircular canal.
- Headache and migraine are also often mentioned by patients showing other symptoms of SCDS. A direct causal link has yet to be proven.
Causes
According to current research, in approximately 2.5% of the general population the bones of the head develop to only 60-70% of their normal thickness in the months following birth. This genetic predisposition may explain why the section of temporal bone separating the superior semicircular canal from the cranial cavityCranial cavity
The cranial cavity, or intracranial space, is the space formed inside the skull. The brain occupies the cranial cavity, which is lined by the meninges and which contains cerebrospinal fluid to cushion blows....
, normally 0.8 mm thick, shows a thickness of only 0.5 mm, making it more fragile and susceptible to damage through physical head trauma or from slow erosion. An explanation for this erosion of the bone has not yet been found.
Diagnosis
The presence of dehiscenceDehiscence
Dehiscence can refer to:*Dehiscence is the spontaneous opening at maturity of a plant structure, such as a fruit, anther, or sporangium, to release its contents.*Wound dehiscence is a previously closed wound reopening....
can be detected by a high definition (0.6 mm or less) coronal CT scan of the temporal bone
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...
, 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 Ménière's disease
Ménière's disease
Ménière's disease is a disorder of the inner ear that can affect hearing and balance to a varying degree. It is characterized by episodes of vertigo and tinnitus and progressive hearing loss, usually in one ear. It is named after the French physician Prosper Ménière, who, in an article published...
and perilymphatic fistula. Other diagnostic tools include the vestibular evoked myogenic potential
Vestibular evoked myogenic potential
The vestibular evoked myogenic potential or VsEP is a neurophysiological assessment technique used to determine the function of the otolithic organs of the inner ear...
or VEMP test, videonystagmography
Videonystagmography
Videonystagmography is a technology for testing inner ear and central motor functions, a process known as vestibular assessment. It involves the use of infrared goggles to trace eye movements during visual stimulation and positional changes...
(VNG
VNG
Radio VNG was Australia's national time signal service. It was inaugurated by the Australian Post Office on 21 September 1964.Originally it transmitted on 4500, 7500 and 12000 kHz from Lyndhurst, Victoria...
), electrocochleography
Electrocochleography
Electrocochleography is a technique of recording stimulus-related responses or electrical potentials of the inner ear and auditory nerve. Components potentials of the human electrocochleogram are: cochlear microphonics , summating potentials , and action potential . These potentials can either be...
(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
Tullio phenomenon
Tullio phenomenon, sound-induced vertigo, dizziness, nausea or eye movement was first described in 1929 by the Italian biologist Prof. Pietro Tullio...
) may also be present singly or as part of Ménière's disease, sometimes causing the one illness to be confused with the other. There are reported cases of patients being affected by both Ménière's 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.
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 craniotomyCraniotomy
A craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often a critical operation performed on patients recording, brain imaging, and for neurological manipulations such as electrical stimulation and chemical...
or via a canal drilled through the transmastoid bone behind the affected ear.
Eponym
Increasingly, this disorder is becoming known, both inside and outside the medical profession , as Minor's syndrome, after its discoverer, Dr. Lloyd B. MinorLloyd B. Minor
Lloyd Brooks Minor is an American scientist, surgeon, and provost and senior vice president for academic affairs of The Johns Hopkins University.-Biography:Minor graduated from Brown University with a Sc.B. in 1979 and an M.D. in 1982...
. However, it is important that this disease is not confused with the paralysis and anaesthesia following a spinal injury, also known as Minor's syndrome after the Russian neurologist, Lazar Salomowitch Minor (1855–1942). In the latter case this term is now nearly obsolete.