Chapter 16:
External, Middle, and Inner Ear Anatomy
The ear is organized into three anatomical regions: the external ear, the middle ear, and the inner ear.
External Ear Structure:
Pinna (Auricle): Consists of movable cartilage and skin. Its characteristic shape funnels sound waves into the external auditory canal.
External Auditory Canal: A cul-de-sac to long in adults that terminates at the eardrum (tympanic membrane).
Cerumen Production: The canal is lined with specialized glands that secrete cerumen, a yellow waxy material that lubricates and protects the ear.
Canal Divisions: The outer one-third of the canal is cartilaginous, while the inner two-thirds consists of bone covered by thin, highly sensitive skin.
Lymphatic Drainage: Lymphatic drainage of the external ear flows into the parotid, mastoid, and superficial cervical lymph nodes.
Tympanic Membrane (TM / Eardrum):
Serves as the boundary separating the external auditory canal from the middle ear cavity.
Normal Appearance: Translucent membrane with a pearly gray color.
Structure and Landmarks: Oval and slightly concave, pulled inward at its center by the malleus (one of the middle ear ossicles).
Visible Malleus Structures: The umbo, manubrium (handle), and short process of the malleus show through the translucent drum.
Additional Visible Landmarks: Annulus, pars tensa, pars flaccida, anterior fold, posterior fold, and the cone of light reflex.
Middle Ear Structure:
A tiny, air-filled cavity located within the temporal bone.
Auditory Ossicles: Contains three tiny bones: the malleus, incus, and stapes.
Communication Openings: Contains openings leading to the outer ear and inner ear.
Eustachian Tube: Connects the middle ear with the nasopharynx, allowing the passage of air. It is normally closed, but opens during swallowing or yawning.
Functions of the Middle Ear:
Conducts sound vibrations from the outer ear to the central hearing apparatus in the inner ear.
Protects the inner ear by reducing the amplitude of loud sounds.
The Eustachian tube equalizes air pressure on both sides of the tympanic membrane to prevent membrane rupture.
Inner Ear Structure:
Contains the bony labyrinth, which houses sensory organs responsible for equilibrium and hearing.
Vestibular Labyrinth: Composed of the vestibule and three semicircular canals.
Cochlea: Contains the central hearing apparatus.
Direct examination of the inner ear is not clinically possible; however, its functional integrity can be evaluated through specific testing.
Auditory Physiology and Hearing Pathways
The auditory system functions across three sensory levels: peripheral, brainstem, and cerebral cortex.
Peripheral Level Mechanism:
Transmits sound and converts mechanical sound vibrations into electrical impulses for brain interpretation.
Sound waves striking the tympanic membrane produce mechanical vibrations.
Vibrations pass through the ossicular chain to the oval window and move into the fluid of the cochlea.
Organ of Corti: Located along the basilar membrane, containing receptor hair cells that serve as the sensory organ of hearing.
Bending of hair cells converts mechanical vibrations into electrical action potentials.
Electrical impulses travel via the auditory portion of Cranial Nerve VIII (vestibulocochlear nerve) to the brainstem.
Basilar Membrane Tonotopic Mapping:
Base of the cochlea: Processes high-frequency sound waves.
Middle section of the cochlea: Processes medium-frequency sound waves.
Apex of the cochlea: Processes low-frequency sound waves.
Brainstem Level Mechanism:
Responsible for binaural interaction, which allows localization of sound direction in space and sound identification.
Cranial Nerve VIII sends signals from each ear to both sides of the brainstem.
Brainstem pathways analyze minute differences in intensity and arrival timing of messages between the two ears depending on head position.
Cerebral Cortex Level Mechanism:
The auditory cortex interprets the cognitive meaning of sound and initiates appropriate behavioral responses.
Pathways of Hearing:
Air Conduction (AC): The normal and most efficient pathway of hearing; sound travels through the external auditory canal and middle ear.
Bone Conduction (BC): Alternate route of hearing where bones of the skull vibrate, transmitting sound waves directly to the inner ear and Cranial Nerve VIII.
Types of Hearing Loss and Vestibular Function
Conductive Hearing Loss:
Caused by a mechanical dysfunction of the external or middle ear.
Represents partial hearing loss because the individual can hear sound if the amplitude is increased sufficiently to reach intact inner ear structures.
Causes: Impacted cerumen, foreign bodies, perforated tympanic membrane, pus or fluid accumulation in the middle ear, and otosclerosis.
Sensorineural (Perceptive) Hearing Loss:
Signifies pathology of the inner ear, Cranial Nerve VIII, or auditory cortex regions of the brain.
Increasing sound amplitude may not enable the person to comprehend words clearly.
Causes: Presbycusis (age-related nerve degeneration) and ototoxic medications that damage hair cells in the cochlea.
Mixed Hearing Loss:
A combination of conductive and sensorineural hearing loss existing simultaneously in the same ear.
Equilibrium and Vestibular Function:
The labyrinth within the inner ear constantly feeds information to the brain regarding body position in space.
Consists of three semicircular canals.
Labyrinthine Inflammation: Feeds incorrect positional information to the brain, producing a staggering gait and vertigo.
Developmental Competence and Risk Factors
Adults ( to Years of Age):
Otosclerosis: A common cause of conductive hearing loss in young adults. It is frequently familial.
Pathophysiology: Gradual bone formation causes the footplate of the stapes to fixate in the oval window, impeding sound wave transmission and producing progressive deafness.
Aging Adults:
Ciliary Changes: Cilia lining the external ear canal become coarse and stiff, causing cerumen to accumulate and oxidize, which impairs sound conduction.
Cerumen Dryness: Atrophy of apocrine glands makes cerumen drier.
Impacted Cerumen: A common, completely reversible cause of hearing loss in older adults.
Presbycusis: Age-related sensorineural hearing loss occurring even in quiet living environments.
Pathophysiology: Progressive nerve degeneration in the inner ear or auditory nerve.
Onset: Typically begins in the and progresses slowly.
Clinical Features: High-frequency tone loss occurs first. Sound localization becomes impaired. Loss is aggravated by background noise.
Physical Changes in Pinna and Drum: Loss of pinna elasticity creates pendulous earlobes with linear wrinkling. Coarse, wiry hairs develop at the canal entrance. Eardrums appear whiter, duller, thicker, and more opaque.
Psychosocial Impact: Older adults often feel that others are mumbling, leading to social isolation and withdrawal from family and friends.
Otitis Media (OM) and Risk Factors:
Pathophysiology: Obstruction of the Eustachian tube or reflux of nasopharyngeal secretions into the middle ear cavity. It is one of the most frequent pediatric illnesses.
High-Risk Populations: Native Americans, Alaskan and Canadian Inuits, Hispanics, premature infants, and children with Down syndrome.
Environmental and Behavioral Risk Factors:
Absence of breastfeeding during the first months of life.
Preterm birth.
Secondhand tobacco smoke exposure.
Daycare attendance.
Male sex.
Pacifier use.
Seasonality (higher incidence during fall and winter months).
Bottle-feeding in a supine position: Feeding infants flat on their back allows gravity and sucking pressure to draw nasopharyngeal fluids into the Eustachian tube and middle ear. Parents should hold babies partially upright during feedings.
Health History and Subjective Assessment
Essential Subjective Data Categories:
Earache (Otalgia)
Ear Infections
Ear Discharge (Otorrhea)
Hearing Loss
Environmental Noise Exposure
Tinnitus
Vertigo
Patient-Centered Care Habits
Targeted Health History Questions:
Earache Assessment:
Location: Surface pain versus deep internal head pain. Pain elicited by pushing on the ear.
Character: Dull and aching versus sharp and stabbing. Constant versus intermittent. Effect of head position changes.
Associated Symptoms: Concomitant cold, sore throat, sinus problems, or dental complaints.
Trauma History: Blunt trauma to ear/head, sports injury, or foreign body insertion.
Relief Measures: Interventions tried to alleviate pain.
Infections and Discharge:
History of ear infections during childhood or adulthood; frequency and medical treatments.
Appearance of discharge: Purulent (pus-like) versus bloody. Presence of odor. Correlation between discharge and pain onset.
Hearing Loss Assessment:
Onset: Sudden versus gradual onset.
Character: Loss across all frequencies or difficulty with specific tones.
High-Risk Situations: Conversations, telephone use, listening to television, or background noise at gatherings.
Associated Phenomena: Perception of people shouting or sounds feeling hollow ("under water" or "in a barrel").
Travel History: Recent airplane travel.
Family History: Familial hearing loss patterns.
Coping Strategies and Impact: Use of hearing aids, daily functional impairment, occupational difficulties, feelings of embarrassment or frustration, and reactions of family and friends.
Environmental Noise Assessment:
Exposure to loud noises at home or work (e.g., noise-polluted areas, airports, traffic, heavy machinery, persistent loud music, or gunfire during hunting).
Use of hearing protection (earplugs or protective headphones).
Tinnitus and Vertigo Assessment:
Tinnitus: Experience of ringing, crackling, or buzzing sounds. Exacerbation at night. Current medication profile (evaluating ototoxic agents).
Vertigo: Perception of true rotational motion—either room spinning (objective vertigo) or patient spinning (subjective vertigo). Dizziness, loss of balance, or light-headedness.
Patient-Centered Care:
Ear hygiene methods and ear cleaning habits.
Date of last professional hearing evaluation.
Hearing aid history: Frequency of use, performance, maintenance, cleaning, and battery replacement.
Nonverbal Clinical Indicators of Hearing Loss:
Lip reading or concentrating intensely on the speaker's mouth rather than eyes.
Frowning or leaning forward to hear conversation.
Posturing or turning head to angle the better ear toward sound.
Misunderstanding questions or frequently requesting repetition.
Irritability or exaggerated startle reflex when the examiner raises their voice.
Garbled speech with distorted vowel sounds.
Inappropriately loud voice volume or flat, monotonous speech tone.
Physical Examination Techniques and Otoscopy
Preparation and Equipment:
Patient Positioning: Sitting upright with head positioned at examiner's eye level.
Required Instruments:
Otoscope with a bright light source; fresh batteries providing white light (not yellow) are essential.
Tuning forks in and .
External Ear Inspection and Palpation:
Auricle Size and Shape: Bilaterally symmetrical in size without swelling or tissue thickening. Familial structural variations are normal if asymptomatic.
Skin Condition: Color matches facial skin. Skin intact without nodules, lumps, or ulcerations.
Darwin's Tubercle: A small, painless nodule located at the helix. Represents a normal congenital variation of no clinical significance.
Tenderness Testing:
Pinna Movement & Tragus Manipulation: Move pinna and push firmly on tragus. Structures should feel firm and produce no pain.
Mastoid Palpation: Palpate the mastoid process behind the auricle; should be non-tender.
External Auditory Meatus: Inspect opening size to select appropriate otoscope speculum. Should show no swelling, erythema, or discharge.
Otoscopic Examination Procedure:
Speculum Selection: Choose the largest speculum that will fit comfortably in the ear canal.
Head Positioning: Tilt patient's head slightly away from examiner to bring the obliquely sloping eardrum into view.
Ear Canal Alignment:
Adults and older children: Pull pinna UP and BACK to straighten the S-shaped canal curve.
Infants and children under years: Pull pinna straight DOWN.
Traction Technique: Hold pinna gently but firmly, maintaining continuous traction until the otoscope is completely removed.
Speculum Insertion: Insert speculum slowly along the canal axis.
Bony Canal Precaution: Avoid striking or pressing against the inner bony two-thirds of the canal wall, as it is covered by thin, hypersensitive epithelium that causes pain upon contact.
Viewing the Tympanic Membrane: Gently rotate the otoscope angle to inspect the entire drum circumference and annulus.
Sequence: Always complete otoscopic examination before performing hearing acuity tests; canal occlusion by impacted cerumen can cause false findings of conductive hearing loss.
Handling Otorrhea: Clean any discharge from the speculum tip before examining the opposite ear to prevent cross-contamination.
Assessment of the Tympanic Membrane:
Color and Translucency: Shiny, translucent, pearly gray membrane.
Cone of Light Reflex: Triangular light reflection seen at the position in the right ear and at the position in the left ear.
Ossicular Visibility: The umbo, manubrium, and short process of the malleus are visible through the translucent surface.
Membrane Contour: Flat and slightly pulled inward at the center.
Structural Integrity: Membrane must be completely intact. White dense patches represent scarring from previous otitis media infections.
Hearing Acuity, Tuning Fork, and Balance Testing
Conversational Speech Screening:
Initial evaluation begins during history taking by observing responses to conversational speech.
Direct Inquiry: Ask the patient if they experience hearing difficulty.
If yes: Refer for formal audiometric testing.
If no: Perform the Whispered Voice Test.
Whispered Voice Test Procedure:
Test one ear at a time while occluding hearing in the non-tested ear.
Occlusion Technique: Place finger on the tragus of the non-tested ear and rapidly push it in and out of the auditory meatus.
Examiner Position: Stand to ( to ) behind or to the side of the patient's ear.
Visual Shielding: Cover mouth so the patient cannot lip-read.
Test Delivery: Exhale fully and whisper a series of two-syllable words slowly.
Normal Finding: Patient repeats each whispered word correctly.
Tuning Fork Tests:
Used to differentiate between Air Conduction (AC) and Bone Conduction (BC) hearing pathways.
Activation: Hold tuning fork by the stem and strike tines softly on the heel of your hand.
Weber Test:
Technique: Place vibrating tuning fork stem on the midline of the patient's skull.
Normal Finding: Sound is heard equally in both ears without lateralization.
Conductive Loss Finding: Sound lateralizes to the impaired (poorer) ear because background room noise is blocked in that ear, making bone vibrations sound louder.
Rinne Test:
Technique: Place vibrating tuning fork stem on the mastoid process behind the ear. When patient indicates sound is no longer heard, quickly relocate the vibrating tines in front of the ear canal and ask if sound is still heard.
Normal Finding: Air conduction is greater than bone conduction (AC > BC) bilaterally.
Conductive Loss Finding: Bone conduction is equal to or longer than air conduction (AC = BC or AC < BC).
Sensorineural Loss Finding: Normal ratio intact (AC > BC), but overall sound duration is reduced in both pathways.
Vestibular Apparatus Evaluation (Romberg Test):
Assesses standing balance mediated by the inner ear vestibular system, cerebellum, and proprioceptive pathways.
Technique: Have patient stand erect with feet together and arms at sides. Instruct them to close their eyes and maintain balance for .
Interpretation: Minor body sway is normal. Excessive sway or loss of balance constitutes a positive Romberg sign.
Safety Precaution: Examiner must stand close by to prevent patient falls.
Clinical Abnormalities of the Ear
External Ear Abnormalities:
Frostbite: Redness, discoloration, edema, or tissue necrosis caused by extreme cold exposure.
Otitis Externa ("Swimmer's Ear"): Infection of the outer ear canal skin; features inflammation, erythema, swelling, severe pain with tragus movement, and purulent discharge.
Cellulitis: Spreading bacterial infection of skin and subcutaneous tissues of the pinna; characterized by fever, warmth, edema, and erythema.
External Ear Lumps and Lesions:
Sebaceous Cyst: Soft, elevated nodule located behind the lobule or in the postauricular fold; filled with sebaceous material and occluded sebaceous gland content.
Tophi: Small, hard, non-tender nodules located on or near the helix containing sodium urate crystal deposits characteristic of gout.
Keloid: Overgrowth of scar tissue extending beyond original wound boundaries; common at site of ear piercing.
Battle Sign: Ecchymosis (bruising) over the mastoid process behind the ear; indicates a basilar skull fracture.
Carcinoma: Ulcerated, crusted lesion with indurated margins that fails to heal; typically located on sun-exposed areas of the pinna.
External Auditory Canal Abnormalities:
Excessive / Impacted Cerumen: Canal occluded by dense, dark brown or black wax; causes conductive hearing loss and limits TM visualization.
Foreign Body: Objects (e.g., beads, Lego bricks, insects) lodged in the ear canal; common in children.
Furuncle: Painful, localized red abscess or infected hair follicle in the cartilaginous canal outer portion.
Polyp: Red, vascular granuloma tissue arising from the canal wall or middle ear mucosa through a perforated drum; bleeds easily and produces foul discharge.
Tympanic Membrane Abnormalities:
Acute Otitis Media: Middle ear infection producing deep ear pain, fever, erythema, bulging TM, loss of anatomical landmarks, and loss of light reflex.
Perforation: Tear or hole in the tympanic membrane resulting from acute purulent infection pressure or direct trauma (e.g., slap to the ear, foreign object insertion).
Tympanostomy Tube Insertion: Surgical placement of tiny grommet tubes through the drum to relieve fluid buildup and ventilate the middle ear in chronic otitis media.
Scarred Drum: Dense, opaque white patches on the membrane surface resulting from previous ear infections or myringotomy; usually does not affect hearing.
Clinical Documentation and Practice Questions
Sample Objective and Subjective Charting:
Subjective Documentation Example:
States hearing is good. Denies earaches, ear infections, discharge, hearing loss, tinnitus, or vertigo.
Objective Documentation Example:
Pinna: Skin intact without masses, lesions, tenderness, or discharge.
Otoscope: External auditory canals clear bilaterally without erythema, swelling, lesions, foreign bodies, or discharge. Both tympanic membranes are pearly gray, with light reflex and landmarks intact, no perforations.
Hearing: Whispered words heard bilaterally. Weber test: tone heard midline without lateralization. Rinne test: AC > BC bilaterally.
Clinical Review Questions & Explanations:
Question 1: Which of the following factors may contribute to sensorineural hearing loss?
A. Impacted cerumen
B. Otosclerosis
C. Drugs affecting the cochlea
D. Vertigo
Correct Answer: C. Drugs affecting the cochlea
Explanation: Any mechanical obstruction impeding sound transmission (impacted cerumen, foreign bodies, otosclerosis) causes conductive hearing loss. Pathology of the inner ear due to nerve degeneration or ototoxic drugs affecting cochlear hair cells causes sensorineural hearing loss. Vertigo is a symptom of vestibular disturbance.
Question 2: Which of the following would not contribute to the development of otitis media?
A. Prematurity
B. Positioning during bottle feeding
C. Ethnicity
D. Tinnitus
Correct Answer: D. Tinnitus
Explanation: Tinnitus is a subjective sound sensation and does not cause middle ear infection. Otitis media risk factors include prematurity, bottle feeding in a flat supine position, high-risk ethnicity (Native American, Inuit, Hispanic), secondhand smoke, daycare attendance, male sex, and pacifier use.