In vitro and in vivo determination of the thermal effect of middle ear endoscopy.

During middle ear endoscopy, patients frequently experience vertigo. We theorized that this effect is secondary to heat produced by the scope. We evaluated two Hopkins rods and two fiberoptic scopes to assess the temperature elevation at the lateral semicircular canal (LSCC) of temporal bones and in a live canine model. These results were compared to the results of a standard 44 degrees C water caloric. We demonstrated in both models that the temperature rise at the LSCC increased relative to the scope diameter and that the Hopkins rods produced the same or greater heating effect than a warm caloric. Direct exposure of the thermocouple to the light produced a greater temperature elevation. We conclude that endoscopes produce sufficient heat to induce caloric stimulation of the LSCC. Care should be exercised to prevent the possibility of thermal injury.