near it. This leads to an over-representation of these areas, resulting in an increased perceptual sensitivity to small frequency differences in tones. Vestibulocochlear nerve pathology congenital deformity of the internal auditory canal, neoplastic and pseudo-neoplastic lesions, with special detailed emphasis on schwannoma of the eighth cranial nerve (acoustic neuroma), non-neoplastic Internal Auditory Canal/CerebelloPontine Angle pathology, including vascular loops, Diagnosis Case history Before examination, a case history provides guidance about the context of the hearing loss. major concern pregnancy and childbirth information medical history development history family history Otoscopy Direct examination of the external canal and tympanic membrane (ear drum) with an otoscope, a medical device inserted into the ear canal that uses light to examine the condition of the external ear and tympanic membrane, and middle ear through the semi-translucent membrane. Differential testing Differential testing is most useful when there is unilateral hearing loss, and distinguishes conductive from sensorineural loss. These are conducted with a low frequency tuning fork, usually 512 Hz, and contrast measures of air and bone conducted sound transmission. Weber test, in which a tuning fork is touched to the midline of the forehead, localizes to the normal ear in people with unilateral sensorineural hearing loss. Rinne test, which tests air conduction vs. bone conduction is positive, because both bone and air conduction are reduced equally. less common Bing and Schwabach variants of the Rinne test. absolute bone conduction (ABC) test. Table 1. A table comparing sensorineural to conductive hearing loss Other, more complex, tests of auditory function are required to distinguish the different types of hearing loss. Bone conduction thresholds can differentiate sensorineural hearing loss from conductive hearing loss. Other tests, such as oto-acoustic emissions, acoustic stapedial reflexes, speech audiometry and evoked response audiometry are needed to distinguish sensory, neural and auditory processing hearing impairments. Tympanometry A tympanogram is the result of a test with a tympanometer. It tests the function of the middle ear and mobility of the eardrum. It can help identify conductive hearing loss due to disease of the middle ear or eardrum from other kinds of hearing loss including SNHL. Audiometry An audiogram is the result of a hearing test. The most common type of hearing test is pure tone audiometry (PTA). It charts the thresholds of hearing sensitivity at a selection of standard frequencies between 250 and 8000 Hz. There is also high frequency pure tone audiometry which tests frequencies from