ENI - Ear Flashcards
List the functions of the ear
- Locate directional source of sound
- Collect sound waves and conduct to inner ear
- Transduction and transmission of impulses to brain
- Balance and positional sense
What are the 3 levels of the ear?
- External
- Middle
- Inner
Describe the anatomy of the auricular cartilage
- Flattened distally
- Ridged proximally to form anthelic and tragus
- Changes from cone shaped to tube shaped proximally, concha
Describe the anatomy of the scutiform cartilage
- Rostromedial
- Function is support
What are the limits of the external ear?
Pinna and external ear canal (external auditory meatus) down to tympanic membrane (ear drum)
- L shaped
Describe the anatomy of the annular cartilage
- Ring shaped
- Attaches other cartilages to bone of bulla
Describe the anatomy of the acoustic process
- Ligamentous attachments to skull
- Attaches to cartilages
What is the vascular supply to the external ear?
- Auricular arteries (from internal carotid)
- Venous drainage to internal maxillary vein
Describe the innervation of the external ear
- Motor nerves to auricular muscles (auriculopalpebral branch of CN VII facial)
- Sensory: branch of CN V trigeminal, cervical segmental C2
What structures are adjacent to the external ear?
- Parotid salivary gland
- Blood vessels (auricular artery, superficial temporal arteries, branches of external carotid, external maxillary vein)
- Nerves
What nerves run close to the external ear?
- Facial nerve (rostroventrial to horizontal canal)
- Auriculotemporal branch of mandibular portion of trigeminal nerve (rostral to vertical canal)
Describe the integumentary covering of the external ear
- Tightly adherent, except Henri’s pocket on caudal pinnal edge
- Thin, squamous stratified keratinising epidermis
- Thin dermis containing adnexal structures
- Hair follicles variable density
- Glands present
- Connective tissue underneath and tehn cartilage
Describe the glands of the external ear
- Sebaceous more prominent distally
- Apocrine, ceruminous
- Increased density proximally
- Sebaceous glands closer to epidermis than apocrine
Describe the histological appearance of the sebaceous glands of the external ear
Large foamy appearance, lipid containing cells
Describe the histological appearance of the apocrine glands of the external ear
- Simple cuboidal epithelium
- Watery secretion
Compare the types of secretion in different parts of the external ear canal
- Distally more lipidy (sebaceous glands)
- Proximally more watery (apocrine glands)
Describe hair within the external ear
- Differs by breed and species
- Sebaceous glands associated with follicles
- Number of hairs in ear canal does not equate to ear disease
Describe the tympanic membrane
- Epithelial
- Boundary betwen external and middle ear
- Stratified keratinising epithelium laterally (outer part)
- Thin lamina propria
- Cuboidal mucosal epithelium medially (middle ear side)
- Scattered secretory goblet cells
- Pars flaccida and pars tensa present
Describe the normal cleaning mechanism of the tympanic membrane
- Migration of cells centripetally from middle at level of stratum granulosum
- Upward epithelial migration proceeds distally
Describe the pars flaccida of the tympanic membrane
- Thicker part
- Dorsorostrally
- Adjacent to malleus
Describe the pars tensa of the tympanic membrane
- Thinner
- Centrally
- Translucent
Describe the appearance of the malleus at the level of the tympanic membrane
- Manubrium of malleus visible
- C-shaped
- Closely associated with collagen in lamina propria
Describe the middle ear
- Tympanic cavity in tympanic bulla
- Contains auditory ossicles
- Connected to nasopharynx via eustachian tube
- 3 compartments
What are the 3 compartments of the the middle ear?
- Epitympanum
- Mesotympanum
- Hypotympanum
Describe the epitympanum
- Dorsal, smallest compartment
- Contains malleus and incus
Describe the mesotympanum
- Tympanic memrbane laterally
- Bony promontory medially
- 3rd ossicle stapes attached to oval window
- Round window and opening to auditory tube
Describe the hypotympanum
- Fundus
- Blind ending cavity
What is unique about the hypotympanum of the cat
Incomplete bony septum dividing hypotympanum
Describe the anatomy of the auditory ossicles
- Supported by ligaments and muscles
- Variation of relative position affects tension of tympanic membrane
Describe the integument of the middle ear
- Cuboidal to columnar epithelial lining
- Mucosal origin, secretory goblet cells
Describe the location of the eustachian tube
Runs dorsolaterally/ventromedial to the nasopharynx
Describe the integument of the eustachian tube
- Pseudostratified, ciliated, columnar epithelium
- Density increases towards nasopharynx
- Scattered goblet cells
- More prominent at tympanic cavity end
What is the function of the goblet cells in the eustachian tube?
- Surfactant secretion to keep tube patent
- Lecithin, lipids mucopoysaccharides
What nerves run close to the wall of the bulla?
- Facial nerve CNVII
- Branches of facial nerve and vagus CNX
- Post-ganglionic fibres of cervical sympathetic trunk
Describe the path of the facial nerve CNVII with relation to the bulla
- In facial canal in petrous temporal bone
- Exposed in dorsal cavity
- Then exits via stylomastoid foramen
Describe the path of the branches of the facial nerve and the vagus CNX nerves in relation to the bulla
- Form tympanic nerve
- Transverse cavity to form lingual nerve and pre-ganglionic parasympathetic fibres to salivary glands
Describe the post-ganglionic fibres of the cervical sympathetic trunk in with respect to the bulla
- Dorsomedial wall of tympanic cavity
- In cat runs in dividing septum
- Joins CNIV to eye
- Diseases leads to Horner’s syndrome
Describe the inner ear
- Contained within petrous temporal bone
- Cochlea, vestibule and semicircular canals
- Encased in bony labyrinth of petrous temporal bone
What functions is the inner ear responsible for?
- Hearing
- Balance
- Position and rotation of head in relation to gravitational forces
What methods can be used to investigate ear disease?
- Cytology of external ear
- Otoscopy
- Radiography
Describe the normal microflora of the external ear
- Same as skin
- Staphylococci
- Malassezia in particular
Discuss the role of cerumen in aural health
- Provides protective antimicrobial layer
- Contains immunoglobulins and exfoliated cells
Describe the composition of cerumen
- Exfoliated cells (squames discarded and shed as part of cerumen)
- Sebaceous secretions (high lipid content, various classes of lipids)
- Ceruminous (apocrine) gland secretions (more aqueous)
- Immunoglobulins IgA, IgG, IgM (mostly IgG)
Describe the role of epithelial cell migration in aural health
- Carries exudate in ear to surface removing cerumen and debris
- Epithelial cells move laterally from centre of tympanic membrane to periphery
- Then desquamate to contribute to production of cerumen
- May be impeded by disease
Give an example of how middle ear disease may occur
- Producing too much mucus
- Can fill middle ear with fluid
What are the consequences of a ruptured tympanic membrane in terms of flushing the ear?
- If ruptured, need to put in ET tube
- If not, fluid will go down eustachian tube into pharynx
- Will drown patient
Define otitis
Inflammation of the ear
- Can be distinguished as externa, media and interna
Describe radiographic imaging of the ears
- Dosoventral, rostrocaudal, open mouth
- Allows comparisons between left and right sides
- In each view, tympanic bulla will be superimposed on other structures
Describe the categories that risk factors for ear disease are subdivided into
- Primary factors: initiate inflammation in a normal ear
- Predisposing factors: increase risk of otitis externa but don’t cause it on their own
- Secondary factors: do not induce, but prevent resolution of the disease once established
Give examples of primary risk factors for ear disease
- Allergic dermatitis (atopic dermatitis)
- Grass awns
- Otocariasis
- Ectoparasites
- Foreign bodies
- Keratinsisation disorders
Give examples of predisposing factors for ear disease
- Overtreatment (e.g. antibiotics)
- Ear pinnae and canal conformation
- increased moisture
- Trauma
- Obstruction
- Ear canal stenosis
- Tympanic membrane perforation
Give examples of secondary risk factors for ear disease
- Opportunistic infection
- Yeast and bacteria
What are the indications for carrying out radiography of the tympanic bullae?
- Persistent otitis externa
- Signs of otitis media including head tilt
- Swellings assocaited with eithe rinfection or neoplasia
- Abnormalities of TMJ e.g. dislocation, dysplasia
What is the greatest cause of obstruction in radiography of the tympanic bullae?
Body of mandible
Describe the positioning for open-mouthed rostrocaudal imaging of the tympanic bullae of the dog
- Dorsal recumbency, pulls and secure forelimbs caudally
- Flex neck at atlanto-occipital joint
- Hard palate roughly vertical to cassette, nose pointing cranialy so hard palate and beam form 30degree angle
- Tongue against lower jaw, secure head
- Lower jaw exteneded and secured caudally with bandage
- Ensure no axial rotation
- Remove ET tube prior to exposure
What is teh centring for open-mouthed rostrocaudal radiography of the tympanic bullae in the dog?
The base of the tongue
What is the collimation for open-mouthed rostrocaudal radiography of the tympanic bullae in the dog?
- Cranial: interpupillary line
- Caudal: in line with chin
- Lateral: outer skin surfaces
Describe radiographic changes that occur with otitis media
- Increased opacity of normally air filled bulla
- Thickening of bulla wall
- Sclerosis of petrous temporal bone
- Rarely increased size of bulla
- Ossification of horizontal canal cartilage
Describe the radiographic changes that may occur with neoplasia of the ear
- Lysis and distortion of wall of bulla
- Soft tissue swelling of adjacent region
What are the components of an aural examination?
- Assessment of external ear: pinnae, external acoustic meatus
- View from outside
- Palpation of auditory meatus
- Look for erythema, exudate, odour, chronic thickening or lichenification
- Otoscopy
What may be seen on otoscopy?
- Erythema or hyperplasia of mucosa
- Ulceration of mucosa
- Exudate
- Neoplasms
- Foreign bodies
- Otodected cynotis (ear mite)
- Tympanic membrane
Describe the examination of cerumen/exudate for ear mites
- Small amount of liquid paraffin on clean micro sclide
- Sample exudate with cotton bud
- Transfer to paraffin on slide, break up if needed
- Place coverslip on top
- View systematically under x4 objective
Describe cytology of otic exudate
- Cotton bud into ear canal to level of horizontal canal, sample exudate
- Roll sample onto clean slide
- Repeat on other ear using clean end/new bud
- Put sample on opposite side of slide, label
- Stain with DiffQuik
What are the signs of damage to the facial nerve?
Facial paralysis
What are the signs of damage to the vestibulocochlear nerve?
- Head tilt
- Nystagmus
- Deafness
What are the signs of damage to the sympathetic fibres near the ear?
- Horner’s syndrome
- Miosis
- Ptosis
- Enopthlamos
- Nictitating membranes protruding
What may the presence of rods on ear cytology commonly indicate?
Pseudomonas
