Superior Semicircular Canal Dehiscence Surgery

Superior semicircular canal dehiscence (SSCD) was first described by Lloyd Minor in 1998 as a syndrome caused by absence or thinning of bone separating the superior semicircular canal from the middle cranial fossa (or rarely from the superior petrosal sinus). The dehiscence creates an abnormal third mobile window in the inner ear in addition to the round and oval windows, allowing pressure transmission and acoustic energy to abnormally activate the superior canal.

Symptoms include sound-induced vertigo (Tullio phenomenon), pressure-induced vertigo (Hennebert sign), autophony (hearing one's own voice loudly), pulsatile tinnitus, hyperacusis to internal sounds (chewing, footsteps, eye movements), aural fullness, and conductive hyperacusis (low-frequency conductive hearing loss with intact bone conduction). Diagnosis combines clinical history, vestibular evoked myogenic potentials (VEMP) with reduced thresholds, audiometry showing low-frequency air-bone gap with normal middle ear, and high-resolution temporal bone CT with sub-millimeter Pöschl reformats.

Surgical treatment is reserved for symptomatic patients with disabling symptoms unresponsive to conservative measures (avoidance of triggering sounds, vestibular rehabilitation). Approaches include middle cranial fossa craniotomy with canal plugging, middle fossa with canal resurfacing, transmastoid plugging, and round window reinforcement. Each approach has trade-offs in surgical morbidity, recurrence risk, and hearing preservation. Plugging is most definitive but carries higher risk of vestibular dysfunction; resurfacing is less invasive but more prone to recurrence.