Otoconia

Otoconia are small calcium carbonate crystals located in the otolithic membranes of the sensory maculae within the utricle and saccule of the vestibular system. They are embedded in a gelatinous layer that covers the hair cells of these otolith organs and contribute to the sense of gravity and linear acceleration.

Mechanism of sensing relies on inertia. When the head moves, the otoconia lag momentarily behind the movement of the surrounding membrane. This dragging of the gelatinous otolithic layer deflects the stereocilia of the hair cells, producing a change in neural activity that signals head position and linear motion. The utricle primarily detects horizontal acceleration, while the saccule detects vertical acceleration; together they help maintain balance and orientation.

Clinical relevance includes disorders related to otoconia, most notably benign paroxysmal positional vertigo (BPPV). In BPPV, otoconia dislodge from the utricle and migrate into the semicircular canals, where they abnormally stimulate hair cells during head movements, causing vertigo and nystagmus. Otoconia can also deteriorate with age, or be damaged by trauma or infection, reducing otolith function and vestibular sensitivity.

Diagnosis and treatment focus on restoring proper otolith function and compensating for vestibular deficits. Diagnostic maneuvers such as the Dix-Hallpike test help identify canalithiasis-related BPPV. Treatments include canalith repositioning maneuvers (for example, the Epley maneuver), other positional therapies, and vestibular rehabilitation therapy to improve balance and reduce vertiginous symptoms.