Calcium carbonate crystals inside the inner ear that sense gravity and straight-line acceleration. When they break free and enter the semicircular canals, the result is BPPV.
Medical definition
The term “otolith” comes from the Greek for ear stone. In clinical vestibular medicine, otolith usually refers to the sensory system of the utricle and saccule — two fluid-filled chambers in the inner ear that detect linear acceleration and gravity. Each chamber contains a membrane studded with calcium carbonate crystals called otoconia. These crystals add weight to the membrane, allowing it to shift when the head tilts or the body accelerates. The shift bends hair cells, which send a signal to the brain about the direction of gravity or movement. The terms otolith and otoconia are often used interchangeably in clinical practice, though strictly speaking an otolith is the entire sensory organ and otoconia are the crystals within it.
Why it matters for vertigo
The utricle and saccule are where BPPV begins. When otoconia detach — due to aging, head trauma, vitamin D deficiency, or prolonged bed rest — they fall into one of the three semicircular canals. There, any head movement that rolls the crystals through the canal triggers a false rotation signal. This is canalithiasis. If the crystals stick to the cupula at the end of a canal instead of floating freely, the result is cupulolithiasis. Both variants cause positional vertigo. Both are mechanical problems with a mechanical solution: a repositioning maneuver that guides the crystals back out.
Where I see this in clinic
Otolith dysfunction is behind most of what I treat. BPPV accounts for roughly 40% of all vertigo cases, and every BPPV case starts with a displaced otoconia crystal. Otolith dysfunction also plays a role in Meniere’s disease, where endolymphatic hydrops alters the otolith membrane, and in conditions like mal de debarquement and PPPD where otolith recalibration after a vestibular event is disrupted. Measuring otolith function directly is possible with VEMP testing — cervical VEMP for the saccule, ocular VEMP for the utricle — though this is not always available outside tertiary centres.
Related terms
Otoconia — the individual crystals within the otolith organ. Canalithiasis — what happens when otoconia enter a semicircular canal. Cupulolithiasis — when otoconia stick to the cupula. Semicircular canals — the canals the otoconia fall into.
Medical Disclaimer: This glossary entry is for educational purposes only. Consult Dr. Prateek Porwal directly. WhatsApp: 7393062200.