What does the Weber test indicate when it lateralizes to one ear?

The Weber test is a simple bedside test used to assess hearing and helps to differentiate between conductive and sensorineural hearing loss. When the tuning fork is placed on the midline of the forehead or skull, sound is transmitted through the bone to both cochlea.

If the test lateralizes to one ear, it indicates that there is a difference in hearing between the two ears. In the case of possible unilateral conductive hearing loss, the sound will lateralize to the affected ear because the conductive loss in that ear allows more bone-conducted sound to be perceived compared to the air-conducted sound, which is diminished. This is due to the inability of the affected ear to adequately transmit sound through the air, allowing the bone-conducted sound to be more prominently perceived in that ear.

In contrast, if the test lateralized to the opposite ear, it suggests sensorineural hearing loss in the ear that does not hear the sound as well. The normal ear hears the sound clearer because nerve transmission is intact, while the affected ear with sensorineural loss cannot perceive the sound effectively.

Thus, lateralization of the Weber test to one ear indicates possible unilateral conductive hearing loss in that ear.