Semicircular Canal Dehiscence Syndrome and Vestibular Dysfunction Disqualify a Military Student Pilot

Humans detect motion and gravity via the labyrinthine system of the inner ear, which consists of the vestibule and the semicircular canals. The vestibular system provides three major functions for maintaining balance and orientation. First, it maximizes the effectiveness of the visual system. Second, it provides orientational information necessary for performing both skilled and reflexive motor activities. Third, in the absence of vision, the vestibular system provides a reasonably accurate perception of motion and position. Although these organs provide important cues for basic orientation on the ground, they often provide misleading information during flight. A superior semicircular canal dehiscence can cause an individual to experience disorientation and vertigo-like symptoms.

A 30-yr-old male student pilot experienced airsickness on his first several flights in the T-6A Texan II aircraft. Airsickness is common among student pilots in the early stages of flight training; however, the subject pilot's symptoms lasted well beyond the normal 24 h, and included vertiginous symptoms lasting days after his last flight. His persistent symptoms required he be held out of training for further evaluation. Comprehensive vestibular and audiological testing were normal; however, a CT scan of the temporal bones showed a left superior semicircular canal dehiscence, and he was diagnosed with left labyrinthine fistula as the cause of his vertigo. He was medically eliminated from pilot training and permanently disqualified from U.S. Air Force flying duties.

Spatial disorientation remains one of the deadliest factors related to aircraft mishaps every year. In this case, an abnormal presentation of airsickness that prompted further evaluation may have prevented a dangerous situation in the air. In standard airsickness, the goal is to keep the pilot flying to expedite adaptation, so this case highlights the importance of distinguishing between normal airsickness and a spatially disorienting medical condition.Dreibelbis JA, Organ BE. Semicircular canal dehiscence syndrome and vestibular dysfunction disqualify a military student pilot. Aerosp Med Hum Perform. 2018; 89(10):923-926.