Weber test

TECHNIQUE: A vibrating 512 Hz tuning fork is placed on the midline of the forehead, vertex, or glabella (or upper incisors). The patient reports whether the sound is heard louder on one side or equally on both sides. Normal: sound heard equally in both ears (no lateralization).

INTERPRETATION: - Conductive hearing loss (outer/middle ear problem): sound LATERALIZES TO THE AFFECTED (diseased) ear. Mechanism: the affected ear is less masked by ambient environmental noise, and bone conduction bypasses the conductive defect, so the cochlea on that side perceives the sound as louder. Causes: cerumen impaction, otitis media with effusion, tympanic membrane perforation, otosclerosis, cholesteatoma. - Sensorineural hearing loss (cochlea, CN VIII, central pathway): sound LATERALIZES TO THE UNAFFECTED (normal/better) ear because the damaged cochlea or nerve cannot transduce the signal normally. Causes: presbycusis, noise-induced hearing loss, Ménière disease, acoustic neuroma (vestibular schwannoma), ototoxic drugs (aminoglycosides, loop diuretics, cisplatin). - Symmetric bilateral loss (e.g., presbycusis) or normal hearing: no lateralization.

MNEMONIC: "Conductive = Combines with the Crummy ear (lateralizes to the bad ear); Sensorineural = Sound goes to the Sound ear (good ear)."

COMBINING WITH RINNE (air conduction [AC] vs. bone conduction [BC] at the mastoid): - Normal: AC > BC (positive Rinne) bilaterally; Weber midline. - Conductive loss: BC > AC (abnormal/negative Rinne) in the affected ear; Weber lateralizes to the affected ear. - Sensorineural loss: AC > BC (positive Rinne, both reduced proportionally) in both ears; Weber lateralizes to the normal ear.

HIGH-YIELD POINTS: - Weber is more sensitive for detecting unilateral conductive loss, and a conductive loss of about 5 dB or more can cause lateralization. Rinne becomes abnormal at about 20-30 dB or more of air-bone gap. - Weber is a screening test only. Audiometry is the definitive evaluation. - Otosclerosis: conductive loss from stapes footplate fixation (stapes ankylosis), with a positive family history, onset in young adulthood, and possible worsening in pregnancy. Weber lateralizes to the affected ear, and there is a classic Carhart notch on audiometry. - Paracusis of Willis: patients with otosclerosis hear better in noisy environments. - A unilateral sensorineural loss with Weber lateralizing away from the affected ear should prompt consideration of acoustic neuroma (CN VIII; associated with NF2, bilateral in NF2). Also consider MRI of the internal auditory canal for asymmetric sensorineural loss. - Cholesteatoma: keratinizing squamous epithelium in the middle ear causing conductive loss and chronic otorrhea. - Weber and Rinne rely on bone conduction bypassing the outer and middle ear to directly stimulate the cochlea.

CLINICAL VIGNETTE PATTERN: A patient with hearing loss in the right ear; Weber lateralizes to the right and Rinne is negative on the right, so this is right conductive loss. If Weber lateralizes to the left with Rinne positive bilaterally, this is right sensorineural loss.