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Superior canal dehiscence

superior canal dehiscence, superior canal dehiscence symptoms
Superior canal dehiscence syndrome SCDS is a rare medical condition of the inner ear, leading to hearing and balance symptoms in those affected123 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 congenital45 There are also numerous cases of symptoms arising after physical trauma to the head It was first described in 1998 by Dr Lloyd B Minor of Johns Hopkins University, Baltimore, US6

Contents

  • 1 Symptoms
  • 2 Symptoms in detail
  • 3 Causes
  • 4 Diagnosis
  • 5 Treatment
  • 6 Eponym
  • 7 References
  • 8 External links

Symptomsedit

Superior canal dehiscence SCD can affect both hearing and balance to different extents in different people

Symptoms of SCDS include:

  • Autophony – person's own speech or other self-generated noises eg 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 detailedit

  • 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" 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 conductive hyperacusis 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 eg 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 SCDS7
  • 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 canal and middle ear are then abnormally diverted through the superior semicircular canal and up into the intracranial space where they become absorbed instead of being registered as sound in the hearing center, the cochlea Due to the difference in resistance between the normal round window and the pathological dehiscence window this hearing loss is more serious in the lower frequencies and may initially be mistaken for otosclerosis 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 These pressure change thus affect the sound of the tinnitus which 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

Causesedit

According to current research, in approximately 25% 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 cavity, normally 08 mm thick, shows a thickness of only 05 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 foundcitation needed

Diagnosisedit

The presence of dehiscence can be detected by a high definition 06 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 fistula8 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 eg 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

Treatmentedit

Once diagnosed, the gap in the temporal bone can be repaired by surgical resurfacing of the affected bone or plugging of the superior semicircular canal910 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 Bone cement has been the material most often used, in spite of its tendency to slippage and resorption, and a consequent high failure rate; recently, soft tissue grafts have been substituted11

Eponymedit

Occasionally this disorder has been referred to as Minor's syndrome, after its discoverer, Dr Lloyd B Minor However, that eponym has also been given to an unrelated condition, the paralysis and anaesthesia following a spinal injury, which is named after the Russian neurologist, Lazar Salomowitch Minor 1855–1942 In the latter case this term is now nearly obsolete12

Referencesedit

  1. ^ Minor LB January 2000 "Superior canal dehiscence syndrome" The American Journal of Otology 21 1: 9–19 PMID 10651428 doi:101016/s0196-07090080105-2 
  2. ^ Minor LB, Cremer PD, Carey JP, Della Santina CC, Streubel SO, Weg N October 2001 "Symptoms and signs in superior canal dehiscence syndrome" Annals of the New York Academy of Sciences 942: 259–73 PMID 11710468 doi:101111/j1749-66322001tb03751x 
  3. ^ Minor LB October 2005 "Clinical manifestations of superior semicircular canal dehiscence" The Laryngoscope 115 10: 1717–27 PMID 16222184 doi:101097/01mlg000017832455729b7 
  4. ^ The Hopkins Gazette Mar 8, 1999 VOL 28, NO 25 Melissa Murray: Old Bone Collection Reveals Basis for Some Dizziness
  5. ^ Hopkins Medical News 1999 Jim Duffy: The Clue in the Old Bones
  6. ^ Minor LB, Solomon D, Zinreich JS, Zee DS March 1998 "Sound- and/or pressure-induced vertigo due to bone dehiscence of the superior semicircular ca Surgery" 124 3: 249–58 PMID 9525507 doi:101001/archotol1243249 
  7. ^ Albuquerque W, Bronstein AM September 2004 "'Doctor, I can hear my eyes': report of two cases with different mechanisms" Journal of Neurology, Neurosurgery, and Psychiatry 75 9: 1363–4 PMC 1739236  PMID 15314139 doi:101136/jnnp2003030577 
  8. ^ HopkinsMedicine – Symptoms & Diagnosis of SCDS & Ménière's disease
  9. ^ Otosurgeryorg: Daniel J Lee MD 2008 – Surgical Repair of Superior Canal Dehiscence
  10. ^ Australian Journal of Oto-Laryngology: SCDS – Resurfacing with calcium phosphate bone cement
  11. ^ Teixido M, Seymour PE, Kung B, Sabra O July 2011 "Transmastoid middle fossa craniotomy repair of superior semicircular canal dehiscence using a soft tissue graft" Otology & Neurotology 32 5: 877–81 PMID 21659938 doi:101097/MAO0b013e3182170e39 
  12. ^ synd/1691 at Who Named It

External linksedit

  • The SCDS Society - The Official Web Site
  • Chicago Dizziness and Hearing – Timothy C Hain, MD – Superior Canal Dehiscence
  • Description and discussion of SCDS
  • HopkinsMedicine Winter 2007 – "A Minor Balancing Act" – an SCDS case history
  • ABC News – Health: "Ear-Induced Torture: Maddening Noise, Everywhere" – an SCDS case history
  • Medical paper reviewing surgical treatment
  • Grey's anatomy Season 6 – episode 22: Shiny happy people
  • DiagnoseMe, Season 1 - episode 2: Too Loud to Livesee a case 1

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