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Ear Anatomy, Physiology & Audiology — Complete Study Notes

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136. Physiology of Hearing

• Area ratio of tympanic membrane to oval window (~17:1)
• Lever action of the ossicular chain (~1.3:1)
• Buckling effect of the curved tympanic membrane

• High-frequency sounds → maximal basilar membrane displacement at the base
• Low-frequency sounds → maximal displacement at the apex (tonotopic organization)
• Traveling wave theory — von Békésy (Nobel Prize 1961)

• Inner hair cells (IHC): ~3,500; primary sensory receptors; receive 95% of afferent innervation (CN VIII)
• Outer hair cells (OHC): ~20,000; act as cochlear amplifiers via electromotility (prestin); receive predominantly efferent innervation
• Stereocilia tip links → deflection opens K⁺/Ca²⁺ channels → depolarization → neurotransmitter (glutamate) release → auditory nerve action potential

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137. Anatomy of the Outer Ear (Blood Supply, Innervation)

Auricle

• Cartilaginous skeleton covered by perichondrium and skin (no subcutaneous fat over cartilage)
• Lobule = fat + connective tissue (no cartilage)

• Posterior auricular artery (from external carotid) → posterior surface
• Superficial temporal artery (from external carotid) → anterior surface
• Venous drainage via posterior auricular and superficial temporal veins → external jugular and retromandibular veins

• Greater auricular nerve (C2, C3) — posterior auricle, lobule
• Auriculotemporal nerve (V3) — anterior auricle, tragus
• Lesser occipital nerve (C2) — upper posterior auricle
• Arnold's nerve (auricular branch of CN X) — posterior EAC wall, concha floor → explains Arnold's reflex (ear cough reflex)
• Facial nerve — small contribution

External Auditory Canal (EAC)

• Length: ~2.5 cm; S-shaped in adults
• Outer 1/3 (lateral): Cartilaginous — contains hair follicles, ceruminous glands, sebaceous glands; Fissures of Santorini and foramen of Huschke (potential spread pathways for tumors/infection)
• Inner 2/3 (medial): Bony — lined by thin, adherent skin (no hair/glands)

• Deep auricular artery (from maxillary artery) — bony EAC
• Posterior auricular and superficial temporal arteries — cartilaginous EAC

• Auriculotemporal nerve (V3) — anterior and superior walls
• Arnold's nerve (CN X auricular branch) — posterior and inferior walls
• Facial nerve — small posterior contribution

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138. Anatomy of the Middle Ear (Blood Supply, Innervation)

Boundaries ("The six walls")

Compartments

• Epitympanum (attic): Above tympanic membrane; contains head of malleus, body of incus; separated from mesotympanum by ossicular chain and mucosal folds
• Mesotympanum: Level of tympanic membrane
• Hypotympanum: Below tympanic membrane

Ossicular Chain

1. Malleus — handle (manubrium) attached to tympanic membrane; head articulates with incus
2. Incus — body + long process + lenticular process (articulates with stapes); long process is most vulnerable (single nutrient vessel, no collateral circulation)
3. Stapes — head, anterior/posterior crura, footplate in oval window; smallest bone in the body

Muscles

• Tensor tympani (CN V3) — pulls malleus medially; tensor tympani muscle canal above Eustachian tube; reflex to loud sounds
• Stapedius (CN VII) — pulls stapes head posteriorly; acoustic reflex (protection); loudest muscle in the body relative to size

Blood Supply (Middle Ear)

• Anterior tympanic artery (from maxillary artery via inferior alveolar/ascending pharyngeal) — supply to tympanic membrane
• Posterior tympanic artery (from stylomastoid artery, branch of posterior auricular) — incudostapedial joint
• Caroticotympanic arteries (from internal carotid)
• Petrosal branch (from middle meningeal artery)
• Superior tympanic artery (from middle meningeal)

Innervation (Middle Ear)

• Jacobson's nerve (tympanic branch of CN IX) → tympanic plexus on the promontory → sensory innervation of middle ear mucosa
• Chorda tympani (branch of CN VII) — runs across middle ear between malleus and incus, carrying taste from anterior 2/3 tongue and parasympathetic fibers to submandibular/sublingual glands; exits via petrotympanic fissure
• Sympathetic fibers from carotid plexus

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139. Anatomy of the Eustachian Tube, Functions, and Adult vs. Infant Differences

Anatomy

• Length: ~35 mm in adults (17–18 mm at birth)
• Divisions:
  • Posterolateral bony portion: 11 mm (opens into anterior wall of tympanic cavity, ~4 mm above the floor)
  • Anteromedial cartilaginous portion: 24 mm (lined by pseudostratified ciliated columnar epithelium; toward tympanic end, ciliated cuboidal epithelium)
• Isthmus: Narrowest point at the bony-cartilaginous junction
• Tympanic ostium: Diameter 3–5 mm
• Pharyngeal ostium: Vertical diameter 3–10 mm, horizontal 2–5 mm; opens into the nasopharynx at the level of the inferior turbinate

Opening Mechanism

• Tensor veli palatini (CN V3) — primary muscle opening the ET; dilates the cartilaginous lumen during swallowing/yawning
• Levator veli palatini (CN X/vagus) — acts synergistically in adults
• Pressure ≥200–300 mm H₂O required to initiate airflow
• Pressure differential of ≥90 mm Hg can "lock" the ET ("critical pressure")
• If >100 mm Hg → tympanic membrane rupture risk

Functions (3 main)

1. Pressure equalization — equilibrates middle ear pressure with atmospheric pressure
2. Mucociliary clearance — clears secretions from middle ear toward nasopharynx (normally closed at rest, opens with swallowing/yawning)
3. Protection — prevents retrograde ascent of nasopharyngeal secretions and sound pressure

Adult vs. Infant Eustachian Tube

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140. Anatomy of the Auditory Analyzer (Cochlea)

Scalae (Three Fluid-Filled Compartments)

• Scala vestibuli and tympani communicate at the apex via the helicotrema
• Scala vestibuli communicates with the vestibule at the oval window (stapes footplate)
• Scala tympani communicates with the middle ear at the round window (membranous, energy dissipation)

Walls of the Scala Media

• Floor (basilar membrane): Supports the Organ of Corti; width increases from base (~0.1 mm) to apex (~0.5 mm) — determines tonotopic tuning
• Roof (Reissner's membrane): Separates scala media from scala vestibuli; maintains endolymph-perilymph separation
• Lateral wall (stria vascularis): Highly vascularized; actively secretes K⁺ into endolymph; generates the endocochlear potential (+80 mV) — the driving force for hair cell transduction

Bony and Membranous Labyrinth

• Bony labyrinth → contains perilymph (similar to ECF)
• Membranous labyrinth → contains endolymph (similar to ICF, high K⁺)
• Endolymph produced by stria vascularis; reabsorbed by endolymphatic sac

Modiolus and Auditory Nerve

• Modiolus contains the spiral ganglion (cell bodies of bipolar neurons = 1st-order auditory neurons)
• Dendrites → hair cells; axons → cochlear nerve (CN VIII)

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141. Anatomy of the Vestibular Analyzer (Vestibule, Semicircular Canals)

Vestibule

• Cochlea (anteriorly)
• Semicircular canals (posteriorly)
• Oval window (laterally, stapes footplate)

• Macula = sensory epithelium with hair cells
• Otolithic membrane overlies the macula
• Otoliths (otoconia) = calcium carbonate crystals embedded in membrane
• Movement → shear force on stereocilia → hair cell depolarization/hyperpolarization

Semicircular Canals (SCCs)

• Crista ampullaris = sensory epithelium
• Cupula = gelatinous membrane spanning the lumen; deflected by endolymph flow
• Hair cells: kinocilium + stereocilia; deflection toward kinocilium = excitation; away = inhibition

• Ampullipetal flow (toward ampulla) = excitation
• Ampullofugal flow (away from ampulla) = inhibition
• Anterior/posterior SCCs: opposite convention

• Superior vestibular nerve → utricle, anterior SCC, lateral SCC
• Inferior vestibular nerve → saccule, posterior SCC

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142. Auditory Neural Pathways and Their Nuclei

Pathway (in order)

Key Features

• Tonotopic organization maintained throughout all levels
• Sound localization:
  • Interaural Time Differences (ITD) — low frequencies, processed in superior olivary complex
  • Interaural Level Differences (ILD) — high frequencies
• Efferent pathway: Olivocochlear bundle (OCB/Rasmussen bundle) from superior olivary complex → outer hair cells; modulates cochlear sensitivity
• Acoustic reflex arc: Loud sound → cochlear nerve → cochlear nuclei → superior olivary complex → facial nerve motor nucleus → stapedius contraction; also CN V (tensor tympani)

Cortex

• Right ear advantage for speech (left hemisphere dominant for speech in 95–98% of right-handers)
• Left auditory cortex: speech recognition/production
• Right hemisphere: emotional/tonal aspects of speech

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143. Physiology of Hearing and the Vestibular System

Hearing (Summary of Transduction)

1. Sound wave → vibrates tympanic membrane
2. Ossicular chain transmits vibration → stapes footplate → oval window
3. Perilymph wave → basilar membrane traveling wave
4. Organ of Corti moves against tectorial membrane → stereocilia deflection
5. Tip links stretch → open mechanically gated K⁺ channels → K⁺ influx (from endolymph) → depolarization
6. Voltage-gated Ca²⁺ channels open → neurotransmitter (glutamate) release → auditory nerve fires

Vestibular Physiology

• Head rotation → endolymph lags behind (inertia) → cupula deflects
• Crista hair cells respond → action potentials in vestibular nerve

• Movement → otoconia shift → shear force on stereocilia
• Utricle (horizontal) and saccule (vertical)

• Head movement → compensatory eye movement in opposite direction
• Maintains stable gaze during head movement (tested with doll's eye and caloric tests)
• Gain = eye velocity / head velocity (normal ≈ 1.0)

• Maintains postural stability via vestibulospinal tracts

• Slow phase (compensatory) + fast phase (recovery saccade)
• Named by direction of fast phase
• Caused by asymmetric vestibular input (one side more active than the other)

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144. Eustachian Tube Function Tests

1. Valsalva Test (Active)

• Patient holds nose and performs forced expiration
• Examiner observes TM movement (otoscopy) or pressure change (tympanometry)
• Generates ~20–40 mm Hg of pressure
• Positive (normal): TM moves outward; middle ear pressure equilibrates

2. Toynbee Test (Active)

• Patient swallows while pinching the nose
• Creates negative pressure in nasopharynx → tests ET opening under negative pressure
• Measured by tympanometry before and after

3. Politzer Test (Passive/Active)

• Olive-tipped bulb placed in one nostril; patient swallows while nose is squeezed
• Air forced through nasopharynx into ET
• Used for passive inflation of the ET

4. Catheter Inflation (Eustachian Tube Catheterization)

• Metal ET catheter passed through nose into pharyngeal orifice of ET
• Air insufflated; auscultation via otoscope detects air passage

5. Sonotubometry

• Sound introduced into nasopharynx; microphone in EAC measures sound transmission when ET opens
• Objective measure of ET opening

6. Tympanometry-Based Tests

• Measure pressure before and after swallowing/Valsalva
• If ET normal: pressure equilibrates; tympanogram returns to type A

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145. Tuning Fork Tests (Rinne, Weber, Bing)

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Rinne Test (Topic 154 — See detailed technique below)

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Weber Test (Topic 155 — See detailed technique below)

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Bing Test

• Place vibrating tuning fork on mastoid; occlude/release EAC
• Bing Positive (normal or SNHL): Sound gets LOUDER when EAC is occluded (occlusion effect — prevents energy escape)
• Bing Negative (CHL): No change with occlusion (occlusion effect absent because air conduction pathway already compromised)

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Schwabach Test (Topic 156)

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Summary Table: Tuning Fork Tests

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146. Assessment of Vestibular Functions

1. Romberg Test

• Patient stands with feet together, eyes open then closed (Romberg position)
• Positive Romberg: Falls/sways with eyes closed but not open = loss of proprioception OR vestibular dysfunction (vestibular lesion → falls to the SIDE of the lesion)
• Cerebellar ataxia → sways with BOTH eyes open and closed
• Sharpened (tandem) Romberg: Feet heel-to-toe; more sensitive

2. Gait Tests

• Unterberger/Fukuda Stepping Test: Patient marches in place with eyes closed and arms extended; rotates toward side of vestibular hypofunction (>30–45° rotation = abnormal)
• Tandem gait: Heel-to-toe walking; unsteady = cerebellar or vestibular
• Past-pointing (Barany test): Patient points index finger to examiner's finger; with vestibular dysfunction, both arms deviate to the side of the lesion (with eyes closed)

3. Fistula Test (Pneumatic Otoscopy)

• Increases/decreases external ear canal pressure with a pneumatic otoscope bulb
• Positive fistula sign: Pressure change → nystagmus and/or vertigo
• Indicates a perilymph fistula (abnormal communication between middle and inner ear) OR erosion of the bony labyrinth (e.g., cholesteatoma eroding into the lateral semicircular canal)
• Hennebert's sign: Positive fistula test in the absence of middle ear disease (seen in congenital syphilis, Ménière's disease)

4. Caloric Test (Fitzgerald-Hallpike)

• Warm water (44°C) or cool water (30°C) irrigated into EAC (head at 30° — puts lateral SCC in vertical plane)
• Warm water → fast phase nystagmus TOWARD irrigated ear (COWS: Cold Opposite, Warm Same)
• Cool water → fast phase nystagmus AWAY from irrigated ear
• Canal paresis (CP): Reduced response in one ear compared to other → indicates vestibular hypofunction on that side
• Directional preponderance (DP): Nystagmus more in one direction than the other → suggests central lesion or acute peripheral lesion

5. Rotation Test (Rotary Chair)

• Patient rotated in computerized chair in darkness; VOR response measured
• Assesses bilateral vestibular function (useful when caloric testing is unreliable)
• Normal: VOR gain ~1.0; phase lead and symmetry also assessed
• Better for low-frequency vestibular function

6. Dix-Hallpike Test

• For BPPV (benign paroxysmal positional vertigo)
• Rapidly moves patient from sitting to head-hanging position
• Positive: Geotropic upbeat-torsional nystagmus with latency (1–5 sec), fatigable, transient (<1 min)

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147. Subjective Methods of Hearing Research

Pure Tone Audiometry (PTA)

• Measures hearing threshold (minimum audible level in dB HL) at standard frequencies
• Frequencies tested: 250, 500, 1000, 2000, 3000, 4000, 6000, 8000 Hz
• Two conditions:
  • Air conduction (AC): Via headphones/insert earphones; tests entire auditory pathway
  • Bone conduction (BC): Via bone vibrator on mastoid; bypasses outer and middle ear; tests cochlea + CN VIII
• Air-bone gap: AC threshold worse than BC threshold → conductive component
• Normal hearing threshold: ≤25 dB HL (adults), ≤15 dB HL (children)

Speech Audiometry

• Assesses how well a patient understands speech (distinct from PTA which measures sensitivity)
• Speech Reception Threshold (SRT):
  • Lowest dB at which patient correctly identifies 50% of spondee words (two-syllable, equal-stressed: "baseball," "hotdog")
  • Should correlate with PTA ±10 dB
• Word Recognition Score (WRS) / Speech Discrimination Score:
  • % of monosyllabic words correctly identified at suprathreshold level (usually SRT + 30–40 dB)
  • Normal: ≥90%; Poor: <50% → suggests retrocochlear pathology

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148. Types of Tympanogram

Jerger Classification

Clinical Correlations

• Type B + small ECV → otitis media with effusion (glue ear)
• Type B + large ECV → TM perforation
• Type C → ET dysfunction, early OME, barotrauma
• Type As → otosclerosis, tympanosclerosis
• Type Ad → ossicular discontinuity (traumatic or erosive)

High-Frequency Tympanometry (1000 Hz probe)

• Used in infants <6 months (standard 226 Hz probe gives unreliable results due to compliant ear canal walls)
• Normal infant tympanogram may look like Type A at 1000 Hz

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149. Objective Methods of Hearing Research

1. Otoacoustic Emissions (OAE)

• Present = OHC functioning (does not confirm auditory nerve integrity)
• Absent = OHC dysfunction OR ≥30–40 dB SNHL
• Cannot diagnose auditory neuropathy spectrum disorder (ANSD) alone (OAEs present but ABR absent/abnormal)

2. BERA / ABR (Brainstem Evoked Response Audiometry / Auditory Brainstem Response)

• Records electrical responses of the auditory pathway to clicks, evoked at 0–90 dB nHL
• 5 Waves (Jewett waves I–V):

• Wave V threshold ≈ behavioral threshold (within 10–20 dB)
• Prolonged I–III interpeak latency: Retrocochlear (CN VIII) pathology (e.g., acoustic neuroma)
• Prolonged III–V interpeak latency: Central (brainstem) pathology
• Uses: Neonatal screening, acoustic neuroma detection, intraoperative monitoring, audiometric threshold estimation in infants

3. ASSR (Auditory Steady-State Response)

• Frequency-specific responses to amplitude/frequency-modulated pure tones
• Can test 500, 1000, 2000, 4000 Hz simultaneously in both ears
• Statistically detected; generates an audiogram estimate
• Better than ABR for predicting low-frequency thresholds
• Useful in infants and patients who cannot cooperate for behavioral testing

4. Tympanometry

• Measures middle ear admittance vs. pressure
• Also measures acoustic reflex (stapedius reflex):
  • Ipsilateral reflex: Same ear stimulus and probe
  • Contralateral reflex: Stimulus one ear, probe other
  • Reflex threshold normally 70–100 dB above pure tone threshold
  • Absent reflex: CHL, SNHL >70 dB, CN VII paralysis, brainstem lesion

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150. Anatomy of the Inner Ear

Bony Labyrinth (Outer shell — contains perilymph)

1. Cochlea (anteriorly) — 2¾ turns, modiolus at center, houses hearing
2. Vestibule (centrally) — oval window (stapes), round window
3. Semicircular canals (posteriorly) — 3 canals (lateral, anterior, posterior)
4. Internal auditory canal (IAC) — transmits CN VII (superior compartment) and CN VIII (inferior compartment — cochlear nerve inferiorly, superior/inferior vestibular nerves)

Membranous Labyrinth (Inner — contains endolymph)

• Suspended within bony labyrinth by fibrous strands
• Includes: cochlear duct, utricle, saccule, semicircular ducts, endolymphatic duct and sac

Endolymphatic System

• Endolymphatic duct: Runs through vestibular aqueduct in petrous bone
• Endolymphatic sac: Sits in dural fold posterior to petrous bone; reabsorbs endolymph
• Dysfunction → Ménière's disease (endolymphatic hydrops)

Windows

• Oval window: Stapes footplate; transmits energy from ossicular chain to perilymph
• Round window: Covered by secondary TM; acts as pressure release for cochlear fluid wave

Blood Supply (Inner Ear)

• Labyrinthine (internal auditory) artery — branch of AICA (anterior inferior cerebellar artery) or basilar artery
• Anterior vestibular artery — utricle, anterior/lateral SCCs
• Common cochlear artery → spiral modiolar artery (cochlea) + vestibulocochlear artery (posterior SCC, saccule)
• Terminal circulation (end-artery) → very susceptible to ischemia

Innervation (CN VIII — Vestibulocochlear Nerve)

• Enters IAC → separates into cochlear and vestibular divisions
• Cochlear nerve: Spiral ganglion neurons (in modiolus)
• Superior vestibular nerve: Utricle, anterior SCC, lateral SCC
• Inferior vestibular nerve: Saccule, posterior SCC

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151. Technique of Otoscopy

Equipment

• Otoscope with pneumatic bulb attachment (for pneumatic otoscopy)
• Specula: Choose largest that fits comfortably (2.5–4 mm)

Patient Position

• Adult/older child: sitting upright
• Young child: parent's lap, arm held, head stabilized

Technique — Adult

1. Inspect the auricle and periauricular area first (scars, skin lesions, swelling, fistulae)
2. Straighten the EAC: Pull auricle up, out, and back (superiorly-posteriorly) to align cartilaginous and bony portions
3. Insert speculum gently, directed anteroinferiorly (toward the patient's nose)
4. Brace hand against patient's cheek/temple to prevent injury if patient moves
5. Inspect systematically: EAC skin, cerumen, discharge, foreign bodies

Technique — Child

1. Pull auricle down and back (inferiorly-posteriorly) — EAC is shorter and more horizontal in young children

Normal Tympanic Membrane (TM)

• Color: Pearly grey, translucent
• Landmarks:
  • Cone of light (light reflex): anterior-inferior quadrant
  • Handle (manubrium) of malleus: Runs supero-inferiorly
  • Lateral process of malleus: Small white bump anterosuperiorly
  • Pars tensa: Main larger portion (inferior)
  • Pars flaccida (Shrapnell's membrane): Small superior portion above the lateral malleal folds
  • Annulus fibrosus: Thickened rim of TM in tympanic sulcus
• Quadrants: Divided by handle of malleus + perpendicular line: anterior superior, anterior inferior, posterior superior, posterior inferior

Pneumatic Otoscopy

• Attach pneumatic bulb; create positive/negative pressure
• Normal TM: moves briskly with both positive and negative pressure
• Reduced mobility: Middle ear effusion, TM scarring
• Positive fistula sign: Pressure change → nystagmus/vertigo (perilymph fistula or labyrinthine erosion)

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152. Characteristics of Types and Degrees of Hearing Loss

Types of Hearing Loss

Degrees of Hearing Loss (WHO / ISO Classification)

Key Causes by Type

• Cochlear: Presbycusis (age-related, high-frequency), noise-induced (notch at 4 kHz), Ménière's, ototoxic drugs (aminoglycosides, cisplatin, loop diuretics), viral (mumps, CMV), congenital
• Retrocochlear: Acoustic neuroma (vestibular schwannoma), CN VIII or brainstem lesion — characterized by poor WRS disproportionate to PTA and rollover phenomenon

Audiogram Patterns

• Sloping (high-frequency loss): Presbycusis, noise-induced
• Low-frequency SNHL: Ménière's disease (early)
• Flat loss: Ototoxicity, sudden SNHL
• Cookie-bite (mid-frequency): Hereditary SNHL

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153. Structure of the Organ of Corti

Cellular Architecture (from lateral to medial)

• Outer pillar cells and Inner pillar cells → form the Tunnel of Corti (contains cortilymph — similar to perilymph)
• Cells of Deiters (phalangeal cells): Support outer hair cells; have phalangeal processes extending up to the reticular lamina
• Cells of Hensen: Lateral to outer hair cells
• Cells of Claudius and Boettcher: Further laterally
• Inner sulcus cells (medial side)

Reticular Lamina

• Tight junction barrier between endolymph (above) and cortilymph/perilymph (below)
• Maintained by Deiters' cells + tops of hair cells
• Ensures ionic isolation essential for transduction

Tectorial Membrane

• Acellular gelatinous membrane overlying hair cells
• Attached medially to limbus (spiral lamina)
• Free-standing laterally
• IHC stereocilia: NOT directly embedded (deflected by fluid shear)
• OHC stereocilia: Directly embedded in tectorial membrane

Innervation Summary

• Type I afferent fibers (90–95%): Myelinated; each contacts ONE IHC
• Type II afferent fibers (5–10%): Unmyelinated; each contacts multiple OHCs
• Efferent (medial olivocochlear, MOC): → OHCs; modulates gain
• Efferent (lateral olivocochlear, LOC): → under IHCs; modulates afferent activity

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154. Technique of Conducting the Rinne Test

Purpose

Equipment

Steps

1. Strike the tuning fork against the elbow or knee (not a hard surface) to produce a moderate vibration
2. Bone conduction first: Place the flat base of the vibrating tuning fork firmly on the mastoid process of the test ear; ask patient to signal when they can no longer hear it
3. Immediately transfer the tuning fork with the prongs 2–3 cm lateral to the EAC (parallel to external meatus), without re-striking
4. Ask patient: "Can you hear this now?" or note if they can still hear it

Interpretation

Key Points

• In normal individuals: AC threshold is ~0 dB HL; BC threshold is ~0 dB HL; but AC is always perceived as louder/longer because air conduction uses ossicular amplification
• Rinne becomes negative when CHL ≥25–30 dB
• Always conduct Weber first to know which ear to test

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155. Technique of Conducting Weber's Experiment

Purpose

Equipment

Steps

1. Strike the tuning fork to produce moderate vibration
2. Place the flat base firmly on the vertex (top center of skull) — alternatively: forehead midline, or lower incisor teeth (most sensitive)
3. Apply firm pressure to ensure good bone contact
4. Ask patient: "In which ear do you hear the sound, or is it in the middle?"

Interpretation

Mechanism of Weber Lateralization

• CHL ear: Background ambient noise is not conducted through damaged middle ear, so the cochlea on the CHL side is less "masked" → BC sound heard louder on that side
• SNHL ear: Cochlea on affected side is damaged → sound lateralizes to the better cochlea

Clinical Examples

• Right TM perforation + CHL right → Weber lateralizes right
• Right acoustic neuroma (SNHL right) → Weber lateralizes left
• Bilateral equal SNHL → no lateralization

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156. Technique of Conducting the Schwabach Experiment

Purpose

Prerequisite

Steps

1. Strike the 512 Hz tuning fork
2. Place the base on the patient's mastoid process
3. Patient signals when they can no longer hear the sound
4. Immediately transfer the vibrating fork to the examiner's mastoid (same side)
5. Note whether examiner can still hear the fork

Interpretation

Limitations

• Examiner must have normal BC; subjective/qualitative test
• Largely replaced by formal audiometry, but remains a useful bedside tuning fork test
• Variability in strike force and mastoid contact pressure affects results

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• Cummings Otolaryngology: Head and Neck Surgery (Chapter 126)
• K.J. Lee's Essential Otolaryngology
• Harrison's Principles of Internal Medicine, 22nd EditionAll 21 topics are covered above. Here's a quick orientation to the notes:

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What's Included

High-Yield Tables to Memorize

• Tuning fork summary table (Topic 145) — CHL vs SNHL vs Normal for all 4 tests
• Tympanogram types (Topic 148) — Jerger A/As/Ad/B/C with clinical correlations
• Eustachian tube: adult vs infant (Topic 139)
• BERA Jewett waves I–V generators (Topic 149)
• Degrees of hearing loss (Topic 152)