Chapter 13: Auditory & Vestibular Systems
A patient complains of hearing loss, and a test reveals the following results. A vibrating tuning fork is placed along the midline of the top of the head, and sound is localized toward the left ear. Then, a tuning fork is placed around the mastoid process of the skull, and the tuning fork is held in the air next to each of the ears at separate times. The sound is perceived as being louder when placed near the right ear. It is concluded that the patient suffers from which of the following?
A. Conduction loss involving the left middle ear
B. Conduction loss involving the right middle ear
C. Sensorineural deficits most likely involving the left cochlear nerve
D. Sensorineural deficits most likely involving the right cochlear nerve
E. Tumor proximal to the cerebellar vermis
D. Several tests can be conducted to distinguish between conduction deafness and sensorineural deafness. These include the Weber test and Rinne test, which were presented in this case. In the Weber test, the sound was localized in the left ear, suggesting that if the loss were conduction deafness, the affected ear would be the left ear. If it were sensorineural loss, the sound would appear stronger on the left side. The convincing feature here is that Rinne test showed that when the sound from the tuning fork was placed near the right ear, it sounded louder, whereas the sound did not appear louder when the tuning fork was placed on the mastoid process of the right side, which would have signified conduction loss on the right side (and likewise for the test when conducted for the left side). Therefore, it is reasonable to conclude that the patient suffers from sensorineural loss on the right side, which quite often may involve an acoustic neuroma affecting Schwann cell sheaths associated with cranial nerve VIII. This argument excludes all other choices except the last choice (E). A tumor of the cerebellar vermis could produce different symptoms, which include principally a wide-based gait ataxia and nystagmus, with no effect on hearing.
A woman visits her physician after experiencing attacks of vertigo, some hearing loss, nausea, vomiting, fullness of pressure in 1 ear, and tinnitus. Tests of cerebellar function are normal. This constellation of symptoms can best be accounted for by the presence of a lesion in which of the following regions?