What characterizes a labyrinthine fistula?

A labyrinthine fistula is specifically characterized as an abnormal opening in the bony capsule of the inner ear. This condition typically results from a defect or rupture in the inner ear structures, which can lead to communication between the inner ear and the surrounding environments, such as the middle ear or the external environment. The presence of this fistula can cause various auditory and balance-related symptoms due to the disruption in the normal functioning of the labyrinth, which is crucial for hearing and equilibrium.

The other options pertain to different ear-related issues. An infection in the middle ear refers to a condition known as otitis media, which primarily affects the middle ear space and does not involve an abnormal opening in the bony structure of the inner ear. Excess fluid in the inner ear could suggest conditions like Meniere's disease, characterized by symptoms such as vertigo and hearing loss but does not define a labyrinthine fistula. Lastly, a blockage of the auditory canal is associated with conductive hearing loss and earwax buildup and is also unrelated to the formation of a fistula within the bony capsule of the inner ear. Thus, the defining characteristic of a labyrinthine fistula is indeed the abnormal opening in the bony capsule of the inner ear.