Otology (including diseases) Flashcards
What are the pinnal conformations in cats?
Erect (normal)
four ears
folded ears
curled ears
What occurs in cats with the four-eared condition?
small extra pinna bilaterally
reduction of the size of their globes
slightly undershot jaw
normal body size
What breed of cat has folded ears?
Scottish Fold
- born with normal ears
- after about 4 weeks the ears fold rostrally
- all have some degree of osteochondrodysplasia of the distal limbs
What breed of cat has curled ears?
American curl
- ears fold back at pinnal apex
What is the musculature of the pinnae like?
muscles of the pinna are numerous and act to move the ear
- Rostroauricular muscles
- Caudoauricular muscles
- Ventroauricular muscle
What is the antitragus?
thin, elongated piece of cartilage caudal to the tragus and separated from it by the intertragic incisure
has medial process, lateral process
What is the intertragic incisure?
the anatomic region used to guide the otoscopic cone or otoendoscope into the ear canal for the otoscopic examination
What is hair like in the ear canal?
most breeds: hairs are fewer, simple, not present the length of the ear canal
- very few fine hairs are found distal to the tympanic membrane
- should decrease in number from distal to proximal
Cocker spaniels: excessive compound hair follicles in the horizontal ear canal
What are ceruminous glands?
modified epitrichial glands in the ear canal
- some open directly onto skin like atrichial glands
Cockers, English spaniels and Labrador retrievers have more than usual
may become hyperplastic with chronic otic disease
- may initially appear as prominent white specks along the canal
- Cockers more prone to hyperplasia
Cerumen formed from exfoliation of cells and glandular secretions
- Protective role with IgA, IgG, IgM – mostly IgG
More are present in the lower 1/3 of the canal
Located below sebaceous glands (like other epitrichial glands)
How does vasculature pass from the concave to convex pinna?
via foramina in elastic auricular cartilage
What is the tragus?
quadrangular plate of cartilage that forms lateral boundary of canal (opposite of anthelix)
What is the anthelix?
low ridge on medial wall of canal
What is the cavum conchae?
circular cavity created by the anthelix, tragus and antitragus
Basal conchae twists as it forms tube (vertical ear canal)
Proximal auricular cartilage creates funnel shape
What is the anular cartilage?
Separate cartilaginous band, overlaps with osseous external acoustic meatus
- Gives ear canal flexibility, articulates with meatus via ligaments
What organisms are present in canine and feline ear canals?
Normal: Staph, Strep, bacillus, E. coli, Corynebacterium, micrococcus, yeast
Otitis: Staph, Strep, Pseudomonas, Proteus, Corynebacterium, Enterococcus, E. coli, yeast
What is cerumen?
Emulsion that coats the ear canal
Contains desquamated keratin, sebaceous and ceruminous excretions
In otitis it has lower lipid content and is more acidic
The clearing mechanism is altered in otitis
What is the pH of dogs ears?
Normal= 4.6-7.2
Otitis:
- Acute= 5.2-7.2
- Chronic= 6.0-7.4 (organisms change?)
How is the tympanic membrane typically oriented relative to the central axis of the horizontal external acoustic meatus in dogs?
45-degree angle
* can be used to advantage when removing saline from ear after flush
How many layers is the tympanic membrane?
3
Inner layer - epithelium from pharyngeal pouch origin
Central layer - fibrous connective tissue from pharyngeal wall
Outer layer - stratified squamous epithelium from pharyngeal groove and part of external ear canal
What is the pars flaccida?
Dorsal part of the tympanic membrane
Has small blood vessels
Can bulge with otitis media due to pressure (rarely found in normal dogs)
Histopathology: collagen, rare mast cells, and keratinized epithelium
- no histopathology difference between bulging and not
What is the pars tensa?
Ventral part of tympanic membrane
Very thin but extremely tough and robust
Has radiating ridges
The stria mallearis is visible
- has a concave shape due to internal surface tension from this attachment
Histopathology: more collagen, no inflammatory cells, keratinized epithelium
What is the stria mallearis and how is it different between dogs and cats?
outline of the manubrium of the malleus visualized through the pars tensa
- tension from this makes the tympanic membrane have a concave shape
Dog: hook- or C-shaped
- concave aspect of the “C” facing rostrally
Cat: straight
Umbo is the point of the greatest depression
How long should a normal tympanic membrane take to heal following a myringotomy?
regenerate by day 14
Complete healing between 21 and 35 days
Will be thicker than normal (scarring)
What maintains the thinness of the tympanic membrane and self-cleaning function of the external ear?
epithelial migration
- tympanum follows centrifugal/outwards pattern of epithelial migration
- never migrates from pars flaccida to pars tensa or vice versa
if it fails you will get cerumen accumulation
What is impedance mismatch?
because fluid has higher impedance than air, a direct transfer of a pressure wave from air to water is insufficient to move through the internal ear fluid compartment
How does the middle ear function to overcome impedance mismatch?
1) the surface area of the tympanic membrane is much larger than the surface area of the foot plate of the stapes on the oval window
2) incus and malleus act as a lever system
*together they amplify the pressure wave
What are the functions of the external ear canal?
Collect sound waves
Conduct sound waves to the tympanic membrane
Determine the origin of the sound waves
What glands do external ear canals have?
Sebaceous glands
Ceruminous glands
What are the parts of the middle ear?
Tympanic membrane
Auditory ossicles
Tympanic cavity
What is the histologic appearance of the tympanic membrane?
Outer and inner epithelium
Core of collagen
Hairless, glandless
What are the two elastic cartilages of the ear canal?
Auricular
Annular
What is the mean middle ear cavity volume of mesaticephalic dogs?
1.5 mL
What three parts can the tympanic cavity be divided into?
Epitympanic recess - smallest, occupied by the head of the malleus and incus
Tympanic cavity proper - adjacent to the TM
Ventral cavity - largest part; contains the septum bulla
- cannot see much of it with a rigid otoscope
What houses the cochlea?
promontory of the petrous portion of the temporal bone
- on the medial wall of the tympanic cavity proper
- opposite the mid-dorsal aspect of the TM
Where is the cochlear (round) window located and what is its function?
caudolateral portion of the promontory
covered by a thin membrane
- oscillates to dissipate vibration energy from perilymph
Where is the vestibular (oval) window located and what is its function?
dorsolateral surface of the promontory
- medial to the pars flaccida
covered by a thin membrane (18-20x smaller than TM)
- stapes should insert into it to transmit sound waves
What is different between the middle ears of cats and dogs?
Dog: bulla septum is a small, incomplete ridge
- only contacts the petrous portion of the temporal bone rostrally
Cat: bulla septum bulla is nearly complete
- separates the tympanic cavity into two compartments
*Dorsolateral (pars tympanica) - smaller, accessed with myringotomy
–> Auditory ossicles, ostium of auditory tube, TM
*Ventromedial (pars endotympanica) - larger, air-filled chamber
- connected through a foramen between septum and petrous bone
- have T-ossicle, conical cartilage in dorsolateral compartment
What is the auditory tube?
Canal from nasopharynx to rostral tympanic cavity proper
- Pressure equalizer
- 3 parts: cartilaginous (medial), junctional, osseous (distal, middle ear)
- Opened by tensor veli palatine
–> Innervated by mandibular branch of trigeminal n (same as tympani)
- may be impaired in brachycephalics
What are the auditory ossicles?
1) Malleus - largest
- manubrium part attaches to the TM
- muscular process attaches to the the tensor tympani muscle
- attaches to the incus
2) Incus - between the malleus and the stapes
3) Stapes - smallest
- anchored in the oval or vestibular window by its annular ligament
- functions as a piston
- stapedius muscle inserts onto it
What is the tensor veli palatini?
This muscle tenses the soft palate to helps equalize air pressure in the tympanic cavity
Associated with the auditory tube
What is the tensor tympani?
This muscle tenses the tympanic membrane, which reduces noise during chewing
Associated with the malleus
What is the stapedius muscle?
a small muscle in the middle ear that stabilizes the stapes bone and reduces sound transmission when exposed to loud noises
*acoustic reflex
What are the common organisms of the middle ear in dogs and cats?
Normal: Staph, Strep, E. coli, Enterococcus, bacillus, Bordatella, Branhamella, Clostridium, yeast
Otitis: Staph, Strep, Pseudomonas, Proteus, Corynebacterium, Enterococcus, yeast
Where are the sympathetic nerves located in the tympanic cavity?
A portion passes through the dorsomedial aspect of tympanic cavity proper near the cochlear window
- In dogs it mostly runs through a channel in the petrous bone
- In cats it more exposed so cats may be more prone to Horner’s
Where is the facial nerve located in the tympanic cavity?
Goes through the facial canal in the petrous portion of the temporal bone
- this is is incomplete within the region of the stapedius muscle
–>around the round window/lateral to the vestibular window
What is the chorda tympani?
Branch of the facial nerve that passes near the pars flaccida before exiting the middle ear to innervate the tongue (taste)
What is the most dense bone in the body?
petrous portion of the temporal bone
forms the medial margin of the middle ear
What is the pathway that nerve impulses travel from the ear to the brain?
Cochlea –>
up the auditory nerve –>
*Cochlear nucleus –>
*Superior olivary complex –>
*Lateral lemniscus –>
*Inferior colliculus –>
*Medial genticulate –>
*Auditory cortex
*part of the central auditory nervous system
How is the cat externa ear canal different than that of a dog?
It is relatively short and straight ear canal
*humans are even more so
Points more anterior not ventral
In which bone of the skull is the inner ear housed?
bony labyrinth within petrous temporal bone
What are the parts of the inner ear?
Bony labyrinth outside, membranous inside
Auditory
*Cochlea
Vestibular
*Vestibule (saccule and utricle)
*Semicircular canals
What is the role of the vestibular system?
Responsible for maintaining equilibrium and balance
Detects static position of head
Detects acceleration, deceleration, rotation
Coordinates head movement with:
-Movement of eyes via vestibulo-ocular projections of CNS
-Movement of trunk and limbs via vestibulo-spinal projections of CNS
What are the 5 organs of the vestibular system?
3 semicircular ducts (anterior, posterior, horizontal - oriented at right angles)
- with 3 ampullae
Utricle and Saccule (the otolith organs)
- each with a macula
What do the semicircular ducts do?
Hair cells to detect endolymph movement
Detect angular acceleration of the head (rotation)
What do the otolith organs do?
Detect linear acceleration of the head
- Utricle: degrees of tilting of the head
–> oriented in a horizontal plane
- Saccule: linear movement in the vertical plane
–> oriented in a vertical plane
What is the crista (ampularis)?
Found in the ampullae of each semicircular canal
Ridge or cone-shaped structure
covered in receptor cells called “hair cells”
- cupula is a gelatinous substance covering stereocilia of hair cells
What is the vestibule of the middle ear?
A perilymphatic chamber that contains the utricle and saccule
What is the structure of the macula of the utricle or saccule and how do they function?
Have support cells & hair cells
Hair cells of macula embedded in gelatinous substance
Over this is a gelatinous substance containing tiny calcium carbonate crystals
–> = otoconia or otoliths
Otoliths have greater density than endolymph so as the head moves, otoliths under the pull of gravity cause deflection of the apical cilia of hair cells
What is the scala vestibuli?
a fluid-filled chamber in the inner ear’s cochlea that spirals from the oval window to the cochlea’s apex
What are the 3 ducts of the cochlea?
- Scala vestibuli - superior
Scala media (cochlear duct) - medial - Scala tympani - inferior
*two main compartments
What is Reissner’s membrane?
Floor of scala vestibuli
Roof of scala media (cochlear duct)
*forms a selective barrier between endolymph and perilymph
Where is the basilar membrane of the cochlea?
Floor of the cochlear duct
Roof of the scala tympani
Which chambers of the cochlea contain perilymph?
Scala vestibuli
Scala tympani
Which chambers of the cochlea contain endolymph?
Scala media
*technically within the membranous labyrinth
What is the difference between endolymph and perilymph?
perilymph: high in sodium and low in potassium
- like cerebrospinal fluid and plasma
endolymph: high in potassium and low in sodium
- probably formed from perilymph by selective ion transport
What is the stria vascularis?
secretory tissue
- plays a role in maintaining the high ratio of K to Na in endolymph
located in the lateral wall of the cochlear duct
has many blood vessels
contains perivascular macrophages that regulate blood vessel permeability
What is the spiral ligament?
A fibrous thickening of the cochlea wall
- Secures the cochlear duct to the bony spiral canal
- Provides mechanical support to the stria vascularis
- Anchors the basilar membrane
What is the path that sound waves take to to transmitted to neurologic signals?
Pinna & external ears collect sound waves ->
deflection of tympanic membrane ->
amplified by ossicles ->
through the vestibular (oval) window/displacement of the round window ->
to perilymph of scala vestibule ->
through to the scala tympani at the apex of cochlea ->
bend hair cell stereocilia (organ of corti) ->
hair cells interact with tectorial membrane ->
depolarize and send signals to cochlear n
What is the helicotrema?
at the apex of the cochlear labyrinth
where the scala tympani and the scala vestibuli meet
How many times do the scalae spiral around the modiolus?
modiolus = central axis, cochlear nerve goes through it
2.5 times
What is the organ of Corti?
Organ that results in hearing
Located in the scala media of the cochlea
Composed of mechanosensory cells, known as hair cells
- sits on the basilar membrane
- 3 rows of outer hair cells
- 1 row of inner hair cells
Surrounded by supporting cells
Covered by gelatinous, collagen containing tectorial membrane
- hair cells are apically embedded in this
What happens to sound waves at the base of the cochlea? Apex?
base (closest to the outer ear)
- basilar membrane is the most stiff and narrow
- high-frequency sounds are transduced (higher number Hz)
apex
- basilar membrane is wider and much more flexible and loose
- low-frequency sounds are transduced (lower number Hz)
What do the outer hair cells of the organ of Corti do?
- Important role in adjusting the tuning and sensitivity of the IHC
- Not actual receptors for hearing
- more susceptible to damage than IHC
How do the hair cells function?
Hair cells are not neurons but are cellular mechanoreceptors
Have highly specialized projections:
- sterocilla (microvilli): many of them, main transducers
- kinocilia (true cillium): one of them, apical, largest
toward kinocilium = depolarizes the cell, release neurotransmitter
away from kinocilium = hyperpolarizes cell, inhibits neurotransmitter release
What do the inner hair cells of the organ of Corti do?
Change sound/fluid waves to neurologic impulses
Fluid waves in the scala vestibuli –> deflection of the basilar membrane
–> causes movement of the organ of Corti and the tectorial membrane
–> apical cilia of hair cells bend
- initially towards kinocilium = release transmitter
- then away = stop neurotransmission
What is the endocochlear potential in the scala media and hair cells?
Endocochlear potential in scala media is +80 mV, plus high K+
Inside of IHC rests around -40 mV
Inside of an OHC is around -60 mV
How do hair cells generate action potential?
There are K channels at the tips of stereocili
Deflecting hair bundle toward kinocilium stretches tips
–> so K+ flows from + charged endolymph into negative interior of hair cells
–> Depolarizes hair cells and opens Ca2+ channels
–> Increases release of neurotransmitter (probably glutamate)
–> neurotransmitters pass to afferent end of auditory nerve
–> nerve fires
How is the intensity of noise determined?
rate of action potentials firing
How is the frequency of noise determined?
part of Organ of Corti that is stimulated
How is the location of noise determined?
Determined by higher CANS centers comparing sounds from both ears
Where are the cell bodies of auditory nerves?
spiral ganglion in cochlea
What is the auditory nerve?
*Connects cochlea with brainstem
*Relay information about intensity, frequency, and timing of a sound
*Cochlear component of CNVIII
*Courses from the cochlea through a small canal in petrous temporal bone
- internal auditory meatus (IAM)
What are some predisposing factors of otitis externa?
Conformation
- stenotic canals
- hair in canals
- long, pendulous pinnae
- breed
Excessive moisture
- swimmer’s ear
- high-humidity climate
Treatment effects
- trauma from cotton swabs
- plucking hair
- irritant antiseptic solutions
- improper abx usage
Otitis media (if primary from URI)
What are some primary causes of otitis externa?
Allergy
Autoimmune/immune-mediated disease
Endocrinopathy
Epithelialization/cornification disorder
Foreign bodies (hair could be in this category)
Glandular disorders
Parasitic
- Otodectes
- Demodex
- Otobius
- Chiggers
Micro-organisms (esp Aspergillus but rare)
Viral (canine distemper)
Neoplasia/polyps
Contact reaction
- rare, occurs on non-haired portion of skin
What are some secondary causes of otitis externa?
Bacteria
Fungi/yeast
Medication reaction (if topical rxn that occurs on inflamed skin only)
Otitis media (if from otitis externa)
Overcleaning
Progressive pathologic changes
What do predisposing factors of otitis externa do?
Facilitate inflammation by permitting alteration of microenvironment
Allow for establishment of secondary infections
What do primary factors of otitis externa do?
Conditions or disorders that initiate the inflammatory process
- Epithelium of the ear canal is just an extension of the rest of the body
- Most cases of otitis are associated with an underlying derm condition
What is the most common primary cause of otitis externa in dogs?
Allergic disease (may be only clinical sign)
What are the most common primary causes of otitis externa in cats?
Parasites, polyps, allergic disease
What should be your top differentials in unilateral otitis externa?
-Foreign body
-Tumor/polyp
-CAFR, AD
+/- otitis media
What do perpetuating factors of otitis externa do?
Sustain and aggravate the inflammatory process
Prevent resolution of the otitis externa
Worsen the otitis externa
What are some clinical signs associated with otitis media (other than ear pain and otitis externa)?
Facial nerve paralysis
- Drooping of ear/lip
- Drooling saliva
- Absent palpebral reflex
- Parasympathetic nose (xeromycteria/dry nose)
- Neurogenic keratoconjunctivitis sicca (KCS)
Sympathetic nerve injury *more common in cats
- Horner’s syndrome
Conductive hearing loss
What is planktonic bacteria?
Classic method of studying bacteria
individual cellular organisms
Free floating
Each cells divides and forms a colony of the same genetic line
- though mutations do occur
What is biofilm?
Group of bacteria
- in a matrix made of polysaccharides, DNA and proteins
- together form an extracellular polymeric substance— SLIME
May be single species or a diverse group of microorganisms
- Mix of bacteria or yeast and fungus
They communicate by a variety of signals which result in changes
- Quorum sensing is one example
Promote survival in harsh environments
What are the clinical signs of Horner’s Syndrome?
Ptosis (drooping of upper lid)
Miosis (contraction of pupil) = results in anisocoria if unilateral
Enophthalmos (backward displacement of eyeball into the orbit)
Protrusion of nictitating membrane
When is the auditory tube open/closed and what are the muscles involved?
Osseous portion = always open
Cartilaginous portion = closed at rest, opens when swallow
- contraction of the levator muscle and tensor palatini muscle
- impaired in brachycephalics
What nerves innervate the pinnae?
trigeminal
facial (CN VII)
vagus
second cervical
What is the pathway of sympathetic innervation?
3-neuron pathway
- central/1st order neuron goes down the spine
- preganglionic/2nd order neuron comes back up the neck
- postganglionic/3rd order neuron goes to the brain
Incus
Cochlea
Malleus
Name the bone
Promontory
Vestibular window
What kind of deafness does this BAER test indicate?
Conductive
What is happening to puppy 1?
Normal hearing
What is happening to puppy 2?
Deaf in left ear
What is happening to puppy 3?
Deaf in right ear
