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Bony Semicircular Canals

canales semicirculares ossei

The three bony semicircular canals (superior/anterior, posterior, and horizontal/lateral) are the osseous labyrinthine structures within the petrous temporal bone housing the membranous semicircular ducts of the vestibular system. Each forms approximately two-thirds of a circle. The superior canal is oriented at right angles to the long axis of the petrous bone and forms the arcuate eminence on the petrous ridge. The posterior canal is the longest. The horizontal canal is the shortest and most medially placed.

Region: Head & Skull

Clinical Relevance

Clinical Notes

The bony semicircular canals are relevant in three clinical scenarios: BPPV (posterior canal most commonly affected, treated by Epley repositioning manoeuvre for canalith repositioning), superior semicircular canal dehiscence (SSCD, thin bone or absent bone over superior canal causing sound- and pressure-induced vertigo and pulsatile tinnitus, treated by plugging the dehiscence from middle fossa approach), and labyrinthine fistula (perilymph leak from canal damage). CT imaging in the plane of each canal demonstrates these conditions.

Pathology

Common Injuries & Conditions

Superior Semicircular Canal Dehiscence

Congenital or acquired absence of the bony covering over the superior semicircular canal creates a third mobile window in the labyrinth producing sound-induced and pressure-induced vertigo (Tullio phenomenon), autophony, and low-frequency conductive hearing loss, diagnosed by high-resolution CT in the plane of the superior canal and managed by surgical plugging.