Conductive versus Sensorineural Hearing Loss (CHL vs. SNHL)
- Let’s sort out clinical audiology using your 512 Hz tuning fork! First, perform the Weber Test: place the vibrating fork on the midline forehead. In CHL, the sound lateralizes (hears louder) in the affected/bad ear. In SNHL, the sound lateralizes to the healthy/good ear!
- Next, perform the Rinne Test: place the fork on the mastoid bone (Bone Conduction), then hold it next to the ear canal (Air Conduction). Normally, Air Conduction (AC) is better than Bone Conduction (BC), which is a positive Rinne (AC > BC).
- If BC > AC (negative Rinne), this indicates a Conductive Hearing Loss (e.g., wax impaction, fluid in the middle ear, or otosclerosis). If AC > BC but the patient hears poorly, it represents a Sensorineural deficit.
Acoustic Neuroma (Vestibular Schwannoma)
- This is a benign, slow-growing tumor arising from the myelin-forming Schwann cells of the vestibular division of Cranial Nerve VIII (vestibulocochlear nerve).
- It is located in the cerebellopontine angle, compressing CN VIII. This leads to slow, progressive, unilateral sensorineural hearing loss, vertigo, and constant high-frequency roaring tinnitus.
- If the tumor grows very large, it can compress CN VII (causing facial weakness) or CN V (causing loss of facial sensation). If you see a patient with bilateral acoustic neuromas, suspect Neurofibromatosis Type 2 (NF2) immediately!
💡 Memory Mnemonic Aid:
Weber lateralizes to the "Affected" ear in Conductive Loss
In conductive block, ambient room noise cannot enter the ear to mask the bone-conducted vibrations, making the sound paradoxically louder on that side.
🌟 High-Yield Boards Summary Indicator:
Undergraduate Viva Pearl: Any patient presenting with progressive, unilateral sensorineural hearing loss and tinnitus must undergo an MRI of the internal auditory canal to rule out an acoustic neuroma!