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Conditions

Superior canal dehiscence

A missing sliver of bone over one balance canal can make you hear your own voice, pulse and eye movements, and can look like otosclerosis on the audiogram. The diagnosis needs symptoms, tests and a scan that agree.

A third window into the inner ear

The inner ear is a fluid-filled space in dense bone with two flexible openings: the oval window, where the stapes pushes sound in, and the round window, which lets the fluid move. Sound passing between them drives the cochlea.

In superior canal dehiscence, the thin bone covering the top of the superior semicircular canal, one of the three balance canals, is missing. The opening usually lies where the canal meets the floor of the middle cranial fossa, the shelf of skull beneath the brain’s temporal lobe; less often it lies against a vein, the superior petrosal sinus.

That opening acts as a third window:

  • Some of the sound entering through the stapes escapes through the opening, so hearing by air falls, mainly in the low pitches.
  • Vibration carried through the skull reaches the inner ear more easily, so bone-conducted sound is heard better than normal.
  • Loud sound and changes in pressure can now move the fluid in the balance canal and stimulate the balance organ.

Lloyd Minor and colleagues described the syndrome in 1998. Their eight patients had vertigo or unsteadiness brought on by sound, or by changes in pressure in the middle ear or inside the head; seven had eye movements, provoked by the same triggers, in the plane of the superior canal, and CT showed missing bone over that canal in each. The condition is still often called Minor syndrome; when a dehiscence causes symptoms, the formal name is superior semicircular canal dehiscence syndrome (SCDS).

Why the bone is missing is not fully understood. In a post-mortem study of 1,000 temporal bones, a complete dehiscence was found in about 0.5%, and very thin bone (0.1 mm or less) in a further 1.4%, often on both sides. The authors suggested that the bone fails to thicken normally after birth.

What people notice

Symptoms range from none at all to disabling. The typical complaints are:

  • Autophony: your own voice sounds loud or booming in the affected ear. Many people also hear their footsteps, chewing, heartbeat, or even their eyes moving.
  • Sound-induced dizziness: a loud noise causes a brief sense of movement, or the visual world seems to jump.
  • Pressure-induced dizziness: coughing, sneezing, straining, lifting or blowing the nose does the same.
  • Pulsatile tinnitus: a rhythmic sound in time with the pulse.
  • A full feeling in the ear, and a hearing loss that looks conductive, usually mild and mainly in the low frequencies.

How it is diagnosed

No single test makes the diagnosis; the symptoms, the function tests and the scan have to agree.

The hearing test. A carefully masked audiogram typically shows a low-frequency air-bone gap with a normal eardrum. Bone conduction may be better than normal, sometimes below 0 dB. The tympanogram is usually normal and the stapedial reflex is usually present; interpreting hearing tests explains why that matters.

VEMPs (vestibular evoked myogenic potentials) record small muscle responses in the neck or under the eyes when the balance organ is stimulated by loud clicks or tones. In a third-window ear it responds to quieter sounds than normal. VEMPs show that the opening is doing something, which a scan cannot.

High-resolution CT of the temporal bone, with very thin slices reconstructed in the plane of the superior canal (the Pöschl view) and at right angles to it (the Stenvers view). Standard planes alone can miss a dehiscence or suggest one that is not there.

The risk of a false-positive scan. When CT measurements were compared with what surgeons found at operation, CT overestimated the size of the dehiscence and could show an opening where the bone was merely very thin. A CT report of “dehiscence” is therefore a finding, not a diagnosis, and without matching symptoms and tests it is not a reason to operate.

Why it can be mistaken for otosclerosis

On the audiogram, superior canal dehiscence and otosclerosis look alike: an air-bone gap, a normal eardrum, the gap mainly in the low frequencies. In otosclerosis the stapedial reflex is absent or shows an early on-off pattern; in a third window it is usually present, because the stapes moves normally. Bone conduction in otosclerosis often dips at 2 kHz (the Carhart notch); in a dehiscence it may be better than normal. Autophony and sound- or pressure-induced dizziness point to a third window.

The distinction matters because stapes surgery cannot close a gap that comes from the inner ear: in these ears it does not help and risks the inner ear (see complex conductive hearing loss). A gap that persists after an otherwise correct stapedotomy is one reason to look for a dehiscence before any revision stapes surgery.

The two can coexist. In a CT series of 663 ears with otosclerosis, 3.5% had a definite dehiscence and a further 2.3% a possible one; up to 8.3% of patients showed one. When both are present the reflexes may be absent, and the decision about surgery is more delicate.

Separating a third window from stapes fixation

With insert earphones and correct masking, suspect a third window when the gap is largest at 250–500 Hz, low-frequency bone conduction is at or below 0 dB HL, the tympanogram is type A, acoustic reflexes are present and the Weber lateralises to the affected ear. Lowered cVEMP thresholds and enlarged oVEMP amplitudes support a third window; in stapes fixation, air-conducted VEMPs are usually reduced or absent. Enlarged vestibular aqueduct, posterior canal dehiscence and cochlear–facial or cochlear–carotid dehiscence give a similar pattern. The author's Utrecht group combined imaging, audiometry, VEMPs and follow-up to tell an anatomical dehiscence apart from a symptomatic patient, including how dehiscence size and location change intracochlear sound pressure (2014–2016; see research). In 104 patients (147 ears), a longer dehiscence went with a larger air-bone gap at 250–1000 Hz and lower cVEMP thresholds, and patients with auditory symptoms had longer dehiscences (median 4.5 against 2.7 mm) beginning closer to the ampulla than those with vestibular symptoms only.

Treatment: living with it, or closing the window

Observation is the right choice for many people. Knowing the cause is often a relief, and avoiding triggers and treating coexisting migraine can make symptoms manageable. A dehiscence found by chance, without symptoms, needs no treatment.

Surgery is considered when symptoms disable daily life and the tests agree. It closes the third window by plugging the canal on either side of the opening, so that its fluid can no longer move, or by resurfacing the opening without blocking the canal; many surgeons plug, or combine the two. Plugging gives up the function of that one canal, and the brain usually adapts. There are three routes:

  • Middle fossa approach: a small window is made in the skull above the ear, the brain’s covering is gently lifted, and the opening is repaired under direct view.
  • Transmastoid approach: the canal is reached from behind the ear through the mastoid bone and plugged without opening the skull, where the anatomy on CT allows.
  • Round-window reinforcement: tissue is placed over the round window through the ear canal to stiffen it. It is less invasive but does not close the opening itself.

What the results show. A 2026 review of 34 studies and 1,130 patients found that 60–95% reported improvement of auditory and balance symptoms after middle fossa or transmastoid repair, with little difference between the two; measured hearing, including the air-bone gap, did not change significantly on average. In a Boston series of 33 patients, mostly plugged through the middle fossa, all improved at first. Three needed a second operation, and six had dizziness lasting more than four months; all six had dehiscences on both sides, migraine, and an opening of 3 mm or more. Round-window reinforcement did less well: in 28 ears followed for an average of 2.4 years, 68% reported overall improvement and 32% needed further surgery.

Risks. Any operation on the inner ear can damage hearing, and unsteadiness for some weeks after plugging is expected. The middle fossa approach adds the uncommon but serious risks of opening the skull. After any ear operation, a sudden drop in hearing or severe spinning vertigo needs contact with your surgeon the same day; see when to contact your surgeon.

When not to operate

Surgery is rarely the right answer when:

  • the dehiscence was found on a scan and there are no matching symptoms;
  • the symptoms, audiogram, VEMPs and CT do not tell the same story;
  • the symptoms are tolerable and the person prefers to live with them;
  • hearing loss is the main complaint, since repair does not reliably improve hearing;
  • another condition, such as vestibular migraine, may explain much of the dizziness;
  • the ear is the only hearing ear.

When both ears have a dehiscence, deciding which one causes the symptoms needs particular care. And stapes surgery is never the treatment for a gap that comes from a dehiscence.

On the other sites

Patient information on superior canal dehiscence from the practice in Colombiers is on grolman-orl.fr.

Sources

  • Minor LB, Solomon D, Zinreich JS, Zee DS. Sound- and/or pressure-induced vertigo due to bone dehiscence of the superior semicircular canal. Arch Otolaryngol Head Neck Surg. 1998;124(3):249-58. PubMed
  • Carey JP, Minor LB, Nager GT. Dehiscence or thinning of bone overlying the superior semicircular canal in a temporal bone survey. Arch Otolaryngol Head Neck Surg. 2000;126(2):137-47. PubMed
  • Tavassolie TS, Penninger RT, Zuñiga MG, Minor LB, Carey JP. Multislice computed tomography in the diagnosis of superior canal dehiscence: how much error, and how to minimize it? Otol Neurotol. 2012;33(2):215-22. PubMed
  • Niesten MEF, Hamberg LM, Silverman JB, et al. Superior canal dehiscence length and location influences clinical presentation and audiometric and cervical vestibular-evoked myogenic potential testing. Audiol Neurootol. 2014;19(2):97-105. PubMed
  • Walker BA, Thorwarth RM, Stull LL, et al. Incidence of concomitant semicircular canal dehiscence with otosclerosis. Otol Neurotol Open. 2022;2(2):e012. PubMed
  • Niesten MEF, McKenna MJ, Grolman W, Lee DJ. Clinical factors associated with prolonged recovery after superior canal dehiscence surgery. Otol Neurotol. 2012;33(5):824-31. PubMed
  • Urichuk M, Azzi J, Woldu B, Hadian A, Hochman J. Comparison of outcomes in superior canal dehiscence surgery using either transmastoid or middle fossa surgical approaches: a systematic review and meta-analysis. J Otolaryngol Head Neck Surg. 2026;55:19160216261435611. PubMed
  • Bunne M, Andersson H, Myhrum M. Long-term outcomes of round window reinforcement for superior semicircular canal dehiscence syndrome. Otol Neurotol. 2022;43(6):709-716. PubMed

Common questions

Why can I hear my eyeballs move?

Hearing your own eye movements, footsteps, chewing or pulse is called autophony, and it is a typical sign of a 'third window' in the inner ear, most often superior canal dehiscence. A gap in the bone lets sound carried through the skull reach the inner ear more strongly than normal. It is not dangerous in itself, but it deserves investigation with a careful hearing test, VEMPs and a fine-slice CT scan.

Can superior canal dehiscence be misdiagnosed as otosclerosis?

Yes. Both cause a conductive-looking hearing loss with a normal eardrum, mainly in the low pitches. The most useful clue is the stapedial reflex: usually absent in otosclerosis, present in a dehiscence. Bone conduction that is better than normal, dizziness provoked by sound or pressure, and abnormal VEMPs also point to a third window. Stapes surgery does not close a gap caused by a dehiscence, so the question should be settled before any operation.

My CT shows a dehiscence. Does that mean I have Minor syndrome?

Not necessarily. CT tends to overestimate the size of a dehiscence and can show an opening where the bone is only very thin, and some people have a true dehiscence without any symptoms. The syndrome is diagnosed when typical symptoms, the audiogram and VEMP tests agree with the scan. A finding on CT alone, without matching symptoms and tests, is not a reason for surgery.

What does surgery for superior canal dehiscence involve?

The aim is to close the third window. Most often the canal is plugged, sometimes also covered, either through a small opening in the skull above the ear (the middle fossa approach) or through the mastoid bone behind the ear (the transmastoid approach). A less invasive option stiffens the round window through the ear canal, but its results are less consistent. The choice depends on the anatomy on CT, the symptoms and the surgeon's experience.

Will surgery for superior canal dehiscence restore my hearing?

Not reliably. Surgery is mainly for disabling dizziness, autophony and sensitivity to sound, and most carefully selected patients report that these improve. In pooled studies, measured hearing, including the air-bone gap, did not change significantly on average. Any operation on the inner ear also carries a small risk to hearing. If hearing loss is the main problem, surgery is rarely the right first answer.

Can I live with superior canal dehiscence without an operation?

Many people can. The condition is not life-threatening, and many find their symptoms manageable once they understand the cause and avoid their own triggers where practical. Surgery is considered when symptoms disable daily life. A sudden drop in hearing always needs prompt medical assessment, and after any ear operation, sudden hearing loss or severe spinning vertigo needs contact with your surgeon the same day.

This page provides general educational information. It cannot replace an individual assessment, which depends on a full history, examination, audiometry and, where relevant, imaging. If you have sudden hearing loss, severe pain, facial weakness, severe dizziness or discharge with fever, seek medical care promptly.