Common cranial nerve examination questions for medical finals, OSCEs and MRCP PACES: vestibulocochlear nerve (VIII)

Question 1:

What is the difference between conductive and sensorineural hearing loss?

Conductive hearing loss is caused by a problem in the external and middle ear.
Sensorineural hearing loss is caused by pathology in the inner ear and further centrally.

What are the Rinne’s and Weber's tests and why are they used?

Rinne’s and Weber’s tests are special examinations using a 512Hz tuning fork to distinguish between conductive and sensorineural hearing loss.
In Rinne’s test, after the tuning fork is struck, it is placed in front of the affected ear (testing air conduction) and then the base of the tuning fork is placed on the mastoid process (testing bone conduction). The patient is then asked when they hear the sound of the tuning fork loudest. Since air conduction is greater than bone conduction the sound of the tuning fork should be heard louder in front of the ear.
In Weber’s test, once the tuning fork is struck, it is placed in the middle of the patient’s forehead and the patient is again asked to note where the sound is loudest (in either ear or in the middle). If the patient has no hearing loss they will hear the tuning fork in the middle of their head.
The following is a summary of the results found and what they mean:

TYPE OF HEARING LOSS IN AFFECTED EAR	WEBER’S TEST	RINNE’S TEST
CONDUCTIVE	Sound heard loudest in affected ear	Bone conduction is louder than air conduction
SENSORINEURAL	Sound heard loudest in unaffected ear	Air conduction is louder than bone conduction

What are the common causes of conductive and sensorineural hearing loss?

Conductive hearing loss: affects the external and middle ear
- External auditory canal: Wax, Otitis externa, Foreign body
- Tympanic membrane : Perforated eardrum
- Middle ear: Otosclerosis, Otitis media
Sensorineural hearing loss: affects the inner ear and more central structures
- Congenital:
  - g. Alport syndrome
- Lesions of the cochlea:
  - Old age, Meniere’s disease, Drugs (gentamicin + loop diuretics – furosemide), Occupational trauma,
- Lesions of the Auditory nerve:
  - Acoustic neuroma, meningitis,
- Brainstem damage:
  - Multiple sclerosis, Infarct

What are the clinical signs of a unilateral cerebellopontine angle (CPA) lesion?

Trigeminal (V) nerve: Reduced facial sensation on affected side + loss of corneal reflex + impaired muscles of mastication
Lower Facial (VII) nerve: Weakness in upper and lower aspects of the face + loss of taste in anterior 2/3rds of the tongue
Vestibulocochlear (VIII) nerve: Sensorineural hearing loss on affected side.
Cerebellar signs
If the Cerebellopontine angle lesion is very large it can extend and affect IX → XII nerves in order
Commonly cerebellopontine angle lesions are caused by acoustic neuromas (vestibular schwannomas) and second most commonly meningiomas, requiring MRI imaging to image the lesion.