Resources
Glossary
The working vocabulary of superior canal dehiscence. Inline dotted terms throughout the chapter link here.
- Acoustic (stapedial) reflex
- A middle-ear muscle reflex to loud sound. PRESERVED in SSCD (the middle ear is normal) but ABSENT in otosclerosis — the key audiologic discriminator for an air–bone gap.
- Air–bone gap
- A difference between air- and bone-conduction thresholds. In SSCD it is a low-frequency PSEUDO-conductive gap (from enhanced bone conduction and shunted air conduction) with preserved reflexes — not true middle-ear disease.
- Autophony
- Hearing one's own voice (and, in SSCD, internal bodily sounds) unnaturally loudly. In SSCD it reflects enhanced bone conduction through the third window; contrast the voice/breathing autophony of a patulous Eustachian tube.
- Bone-conduction hyperacusis
- Abnormally acute hearing of bone-conducted sound — patients may hear their own eye movements, footsteps or pulse. Reflected audiometrically as supranormal (better-than-0 dB) bone-conduction thresholds.
- Canal plugging / resurfacing
- Surgical occlusion (plugging) or recovering (resurfacing/capping) of the dehiscence — via a middle-cranial-fossa or transmastoid approach — to close the third window in disabling disease.
- Hennebert sign
- Vertigo or nystagmus provoked by pressure change in the external canal or by Valsalva/straining — pressure-induced stimulation through the third window.
- Oscillopsia
- The illusory to-and-fro movement of the visual scene, here provoked by sound or pressure as the third window drives the eyes through the vestibulo-ocular reflex.
- Otosclerosis
- Otospongiotic fixation of the stapes causing a true conductive low-frequency loss with ABSENT acoustic reflexes — the principal mimic of the SSCD air–bone gap, distinguished by reflexes, VEMP and CT.
- Pöschl plane
- A CT reformat parallel to the superior canal that displays the canal as a ring, the most sensitive view for a roof dehiscence.
- Round-window reinforcement
- Reinforcing the round window to dampen third-window energy transfer — a less invasive option of more variable and often less durable benefit than canal occlusion.
- Stenvers plane
- A CT reformat orthogonal to the superior canal, used to confirm a true dehiscence and avoid the partial-volume artefact that over-calls thin bone.
- Superior semicircular canal dehiscence (SSCD)
- Absence of the bone covering the superior (anterior) semicircular canal, creating a third mobile window into the inner ear and producing sound- and pressure-induced audiovestibular symptoms.
- Third-window mechanism
- Normally the inner ear has two windows (oval and round). A dehiscence adds a third, so acoustic and pressure energy is abnormally shunted — stimulating the canal and diverting sound from the cochlea.
- Tullio phenomenon
- Vertigo, oscillopsia or nystagmus provoked by loud sound — a hallmark of a third-window lesion such as SSCD. The evoked eye movements align with the affected canal.
- VEMP
- Vestibular evoked myogenic potentials. In SSCD the cervical-VEMP threshold is low and the ocular-VEMP amplitude is high — the third window makes the vestibular organs abnormally sensitive to sound.