Earwax Impaction and Otitis Externa

Excessive Earwax

• Excessive earwax, also known as impacted cerumen, can impede sound passage and cause mild conductive hearing loss.
• It can also cause pain, itching, and dizziness in the ear.
• If left untreated, excessive earwax can lead to hearing loss.

Otitis Externa (Swimmer's Ear)

• Otitis externa is the inflammation of the external acoustic meatus.
• It can be acute (lasting less than 6 weeks) or chronic (lasting more than 3 months).
• The most common cause of otitis externa is a fungal infection.
• Risk factors include swimming, minor trauma from cleaning, using hearing aids, and earplugs.
• Symptoms of otitis externa include ear pain, swelling of the external acoustic meatus, decreased hearing, and pain with movement of the outer ear.

Middle Ear (Tympanic Cavity)

• The middle ear is an irregular bony cavity inside the temporal bone, between the eardrum and inner ear.
• It contains three small bones (auditory ossicles), two small muscles, and the tympanic plexus.
• The membranous (lateral) wall of the middle ear is formed mainly by the tympanic membrane (eardrum).
• The tympanic membrane separates the tympanic cavity from the external acoustic meatus.
• The external surface of the membrane is covered by skin, while the internal surface is covered by mucosa, with a fibrous layer in between.

Membranous (Lateral) Wall

• The handle of the malleus attaches to the umbo of the tympanic membrane.
• The chorda tympani courses at the inner surface of the membrane.
• Politzer's triangle is located at the anteroinferior quadrant of the membrane.

Auditory (Eustachian) Tube

• The auditory tube is a 36 mm long tube formed by bone and cartilage, connecting the tympanic cavity and nasopharynx.
• It allows the passage of air between the tympanic cavity and nasopharynx to equalize pressure on both sides of the tympanic membrane.
• The tensor veli palatini muscle (assisted by salpingopharyngeus) opens the auditory tube to equalize pressure differences.
• The mucosal layer lining the auditory tube is continuous with the mucosa lining the tympanic cavity, allowing upper airway infections to travel through the tube and reach the tympanic cavity, leading to otitis media.

Auditory Ossicles (Ear Bones)

• The three auditory ossicles form a bony chain between the lateral and medial walls of the tympanic cavity.
• They mechanically convert the vibrations of the eardrum into amplified pressure waves in the fluid of the cochlea (or inner ear) by the oval window.
• The names of the bones are malleus, incus, and stapes (MIS) in order.
• The malleus is the largest bone and resembles a hammer in shape.
• The incus resembles an anvil in shape.
• The stapes is the smallest bone in the human body and resembles a stirrup in shape.

Tegmental (Upper) Wall, Jugular (Inferior) Wall, and Labyrinthine (Medial) Wall

• The tegmental wall is the upper wall of the middle ear.
• The jugular wall is the inferior wall of the middle ear.
• The labyrinthine wall is the medial wall of the middle ear, separating the tympanic cavity from the inner ear.
• The oval window is a connection between the tympanic cavity and the scala vestibuli of the inner ear, closed by the base of the stapes.
• The round window is a connection between the tympanic cavity and the scala tympani of the inner ear.

Clinical Note - Otosclerosis

• Otosclerosis is a condition of the middle/inner ear characterized by irregular bone formation.
• The main symptom of otosclerosis is hearing loss, accompanied by loss of balance, vertigo, tinnitus, or a combination of these.
• This condition affects either the stapes (stapedial otosclerosis) or the cochlea (cochlear otosclerosis).

Inner Ear

• The inner ear consists of an empty bony space inside the temporal bone (bony labyrinth) and membranous structures with the same shape inside (membranous labyrinth).
• The structures related to these labyrinths play a crucial role in hearing and balance.

Bony Labyrinth

• The bony labyrinth is the hardest bony part of the human body and is the second hardest structure after the enamel of teeth.
• It surrounds the membranous labyrinth like a shell and is filled with a fluid called perilymph.
• The bony labyrinth consists of three parts: vestibule, semicircular canals, and cochlea.

Vestibule

• The vestibule is located between the cochlea and semicircular canals.
• The utricle and saccule of the membranous labyrinth are found inside the vestibule.

Semicircular Canals

• The semicircular canals are three semi-circular canals (anterior, posterior, and lateral).
• The semicircular canals of the membranous labyrinth are found inside the bony canals.
• They are connected to the vestibule.

Cochlea

• The cochlea is a spiral canal that begins at the vestibule and ends at the apex of the cochlea.
• The cochlear duct (scala media) is filled with endolymph and is located between the scala vestibuli and the scala tympani.
• The helicotrema is the connection between the scala vestibuli and the scala tympani.

Membranous Labyrinth

• The membranous labyrinth consists of numerous ducts connected with each other as a closed system, filled with a fluid called endolymph.
• The parts of the membranous labyrinth include the utricle and saccule, semi-circular ducts, and cochlear duct.

Hearing and Balance

• Decibel (dB) is the unit for measuring sound pressure (intensity of sound).
• Human ear is capable of hearing sounds between 0-140 dB.
• Frequency is the number of occurrences of a repeating event per unit of time, measured in Hertz (Hz).
• Human ear is sensitive to sounds between 20-20,000 Hz, with most sensitivity between 1500-3000 Hz.

Clinical Note - Vestibulo-Ocular Reflex

• The vestibulo-ocular reflex (VOR) is a reflex that acts to stabilize gaze during head movement, with eye movement due to activation of the vestibular system.
• The reflex acts to stabilize images on the retinas of the eye during head movement, holding gaze steadily on a location.
• People with an impaired reflex find it difficult to read using print, because the eyes do not stabilize during small head tremors.

Clinical Note - Oculocephalic Reflex (Doll's Eyes)

• The oculocephalic reflex (doll's eyes reflex) is an application of the VOR used for neurologic examination of CNs III, VI, and VIII, and overall gross brainstem function.
• The reflex derives its name from the characteristic doll's eyes appearance that a patient has if the reflex is positive.