Ears

Ear Disorders Study Notes

Chapter 44 Overview

• Overview of ear disorders with a focus on anatomy and specific conditions affecting hearing and balance.

Anatomy of the Ear

Conductive Phase

• Involves the outer ear and middle ear in sound conduction.

• Important structures include:
    - Outer Ear:
      - Funnel Shape: Conducts sound waves to the tympanic membrane.
      - Ear Canal: Thin layer of epidermis containing fine hairs, sebaceous glands, and cerumen.
      - Functions Altered By: Blockage, inflammation, or drainage.
    - Middle Ear:
      - Air-filled space located between the tympanic membrane and inner ear.
      - Contains three tiny bones known as ossicles:
        - Malleus: Also known as the “hammer.”
        - Incus: Also known as the “anvil.”
        - Stapes: The smallest bone in the body.
      - Connected to the nasopharynx by the Eustachian tube.
    - Inner Ear:
      - Integral for balance and hearing, contains:
        - Cochlea: Main organ for hearing.
        - Cochlear Nerve: Carries auditory signals to the brain.
        - Labyrinth: Comprises bony and membranous structures conducive to balance.

Function of Inner Ear

Balance

• Balance is influenced by:
    - Vision
    - Proprioception
    - Inner ear structure.

• Labyrinth:
    - Consists of:
      - Bony Labyrinth
      - Membranous Labyrinth
    - Key structures include:
      - Utricle & Saccule: Detect linear acceleration.
      - Semicircular Canals: Detect rotational movements.

• Fluids in Inner Ear:
    - Perilymph: Fluid in the bony labyrinth.
    - Endolymph: Fluid in the membranous labyrinth.

• Physical movements create oscillations in fluids, detected by Cranial Nerve VIII (CN VIII)
    - Vestibulocochlear nerve is critical for balance sensation.

Hearing

• Cochlea:
    - Houses the Organ of Corti, spiral-shaped and critical for hearing.
    - Contains perilymph and stereocilia, which are hair cells that respond to sound wave vibrations.

• Mechanism: Activation of stereocilia generates signals transmitted via CN VIII to the brain.

• Decibels (dB): Unit measuring sound loudness.
    - 0 dB: Threshold of hearing.
    - Whisper: 0–20 dB.
    - Normal conversation: 60 dB.
    - Sounds above 85 dB can cause hearing loss.

• Audiometric Testing: Assesses hearing abilities based on sound frequency and loudness.

Hearing Loss

Classifications

• Mild Hearing Loss:
    - Range: 26–40 dB.
    - Difficulty in following conversations.

• Moderate Hearing Loss:
    - Range: 41–55 dB.
    - Hearing aids often required for normal conversations.

• Severe Hearing Loss:
    - Range: 60–90 dB.
    - Can hear sounds but cannot interpret words without observing lips.

• Profound Hearing Loss:
    - Below 90 dB.
    - Requires hearing aids, lip reading, or sign language.

Types of Hearing Loss

• Conductive Hearing Loss (CHL):
    - Disorder affecting sound transmission through outer or middle ear.
    - Common causes include:
      - Impacted cerumen (earwax)
      - Otitis media (middle ear infection)
      - Bone abnormalities.

• Sensorineural Hearing Loss (SNHL):
    - Disorder affecting the inner ear, auditory nerve, or auditory pathways in the brain.
    - Most common cause: Loss of stereocilia in the organ of Corti.

• Central Hearing Impairment:
    - Damage to the brain affecting the ability to interpret sounds (e.g., from stroke or trauma).

• Mixed Hearing Deficiency:
    - A combination of CHL and SNHL.

Hearing Loss in Older Adults

• Presbycusis:
    - Age-related degenerative changes leading to diminished hearing.
    - Typically starts around age 50.
    - Progressive loss of hair cells in cochlea, primarily affecting high-frequency sound perception.
    - Hearing aids are often recommended.

Tinnitus and Vertigo

Tinnitus

• Perception of abnormal sounds in the ears, often described as a “ringing” noise.

• Types:
    - Continuous or intermittent.
    - Can be unilateral (one ear) or bilateral (both ears).

• Causes include:
    - Disorders of CN VIII.
    - Prolonged noise exposure.
    - Infections or medications.
    - Meniere’s disease.

Vertigo

• Characterized by a sense of “room spinning” and exaggerated movement sensations.

• Symptoms may include nausea and vomiting.

• Key differential is to distinguish vertigo from dizziness.

• Often associated with alterations in the inner ear (e.g., Meniere’s disease).

Diagnosis of Ear Disorders

• Audiometry:
    - The primary test for hearing assessment.

• Tympanogram:
    - Measures middle ear response.

• Genetic Testing:
    - May identify hereditary causes.

• Imaging:
    - MRI and CT scans to detect anomalies.

• Auditory Brainstem Response Testing:
    - Assesses neural responses to sound.

• Otoacoustic Emissions (OAE):
    - Tests for cochlear function.

External Ear Disorders

Cerumen Impaction

• Excessive earwax can obstruct ear canal.
    - May cause reversible hearing loss.

• Treatment involves irrigation to remove blockage.

Otitis Externa (Swimmer’s Ear)

• Inflammation of the external ear.
    - Caused by infectious agents/allergies.
    - Water retention in the ear canal predisposes to infections.

• Symptoms:
    - Pain upon movement of the external ear, redness, tenderness, drainage.

Otitis Media

• Middle ear infection often associated with upper respiratory infections (URI).

• Most prevalent in children due to anatomical features of Eustachian tubes.

• Pneumatic Otoscope:
    - Used to visualize decreased movement of the tympanic membrane.

• Symptoms:
    - Fever, earaches, and in children, nonspecific signs (tugging at ears, irritability).

• Potential complications:
    - Tympanic membrane rupture, requiring tympanotomy (incision to promote drainage).

Tympanic Membrane Perforation

• Result of middle ear infection or trauma.

• Symptoms include:
    - Buzzing sound, earache, hearing loss.

• Most small ruptures heal spontaneously within approximately 4 weeks.

• Caution: Ear drops should not be used as they may introduce infection; untreated can cause more severe conditions (e.g., cholesteatoma, mastoiditis).

Otosclerosis

• Abnormal bone growth on the stapes, inhibiting its ability to transmit vibrations.

• Symptoms include:
    - Progressive hearing loss, often unilateral.

• Diagnosis confirmed by audiogram showing conductive hearing loss.

• Stapedial reflex testing reveals limited ossicle movement.

• Surgical option:
    - Stapedectomy: Removal of stapes, often accompanied by prosthesis to restore function.

Inner Ear Disorders

Meniere’s Disease

• Characterized by changes in fluid volumes within the bony and membranous labyrinths.

• Results in:
    - Increased endolymph causing distension in portions of the inner ear.
    - Symptoms include:
      - Progressive hearing loss
      - Tinnitus
      - Episodic vertigo.

• Predominantly affects individuals aged 40–50 years; etiology is largely unknown.

• No specific diagnostic test exists for Meniere’s disease.