Three fluid-filled loops inside the inner ear that detect head rotation in all directions. When these loops are disrupted, the result is vertigo.
Medical definition
The semicircular canals are three bony tubes arranged at roughly right angles to each other inside the labyrinth of the inner ear. They are named by their orientation: posterior, horizontal (also called lateral), and anterior (also called superior). Each canal is filled with a fluid called endolymph and contains a sensory region called the ampulla. When the head rotates, the endolymph moves, bending hair cells in the ampulla, which sends a signal to the brain about the direction and speed of rotation.
Why it matters for vertigo
BPPV, the most common cause of vertigo I see in clinic, happens when calcium carbonate crystals (otoconia) fall out of the utricle and into one of these canals. The posterior canal is affected in about 85% of BPPV cases. The canal involved determines which repositioning maneuver is used. Posterior canal BPPV responds to the Epley maneuver. Horizontal canal BPPV needs the BBQ roll or Gufoni maneuver. Anterior canal BPPV is the rarest variant and, in my practice, responds to the Bangalore Maneuver — a technique I developed after seeing this variant misdiagnosed repeatedly.
Where I see this in clinic
The first step in any vertigo workup is identifying which canal is affected and on which side. The Dix-Hallpike test and the supine roll test produce specific nystagmus patterns that point directly to the affected canal. Without knowing the canal, you cannot choose the right maneuver — and the wrong maneuver can move the crystals into a more difficult position. This is one reason why video-recorded nystagmus (via VNG) is so useful: it removes the guesswork entirely.
Related terms
Otoconia — the crystals that cause BPPV when they enter the canals. Cupulolithiasis — when crystals stick to the cupula rather than floating freely. Endolymph — the fluid inside the canals whose movement generates the vertigo signal. Dix-Hallpike test — the bedside test used to identify which canal is involved.
Medical Disclaimer: This glossary entry is for educational purposes only and is not a substitute for in-person clinical assessment. For a diagnosis and management plan, consult Dr. Prateek Porwal directly. WhatsApp: 7393062200.