Ears PDF - Ear Anatomy & Imaging

Ears 29/09/2024 10:08...

Ears 29/09/2024 10:08 Examining the ear Imaging of the ear Positioning for radiograph Functions: Assessing patient for ear disease: Radiography: Term Definition 1. Locate directional source of sound 1. General clinical exam Otitis Infection or inflammation of the 2. Collect sound waves and conduction to inner ear Are there co-morbidities? 3 main radiographic views of ear and TMJ : ear 3. Transduction and transmission of impulses to brain Is there other skin disease? ○ Dorsoventral 4. Balance and positional sense Are there neurological problems? - vestibulocochlear disease, facial nerves and SNS nerves in the middle ear ○ Lateral oblique ** ○ Rostrocaudal (open mouth) ** External ear Middle ear Inner ear 1. Physical exam of the external portions of the outer ear ** Best for viewing tympanic bulla Look and feel pinna Structure Pinna auricle Encased in bony labyrinth petrous temporal bone Examine canal opening and upper vertical canal - is there a smell? 1. Moved by several auricular muscles Tympanic cavity in tympanic bulla Auditory ossicles Cochlea Dorsoventral positioning Lateral oblique Rostrocaudal 2. Convex and concave surface Vestibule Air filled and inside bony bulla Supported by ligaments and muscles 1. Cytology Semi-circular canals With animal in dorsal recumbency, occipitoatlantal joint Patient normally lies in lateral With animal in dorsal recumbency, occipitoatlantal joint is Variation of relative position = affects tension of tympanic 2. Otoscopy external ear canal (external auditory meatus) down to tympanic membrane: Sensory innervation by cranial nerve 8 is flexed and mouth held open recumbency with side of interest closer to flexed and mouth held open membrane 3. Video-otoscopy 1. Erect pinna - wild type = selective breeding Epitympanum Mesotympanum Hypotympanum or fundus 1. Branches in internal acoustic meatus table and with head rotated (20 - 30°) 4. Imaging - Radiograph, CT and MRI Dorsal and smallest Tympanic membrane Head may be restrained using tapes and sandbags, towards the VD position Head may be restrained using tapes and sandbags, Elastic cartilage for support: Stapes = stirrup Functions: Contains malleus and latteraly although a perspex frame will give much better stability although a perspex frame will give much better stability Incus = anvil 1. Hearing incus - ossicles Bony promontory is Malleus = hammer Auricular cartilage Annular cartilage medial 2. Balance Tongue is placed against the lower jaw and it is wise, Tongue is placed against the lower jaw and it is wise, Stapes attached to 3. Position and rotation of head in relation to gravitational forces although not essential, to remove the endotrachial tube although not essential, to remove the endotrachial tube Flattened distally - furthest part of the head Fits within base of conchal tube of auricular cartilage oval window before exposure to avoid super-imposition over the before exposure to avoid super-imposition over the Clinical relevance: Ridged - forms anthelix (medial) and tragus (lateral) Ligamentous attachments to bony acoustic process of Round window and tympanic bullae tympanic bullae temporal bone of skull opening to auditory Ear disease Prevalence: Cone - tube (concha) proximal tube Exact positioning varies with head conformation, but the Exact positioning varies with head conformation, but the 1. Most common in small animal practice hard palate and beam should form an angle of about 30° hard palate and beam should form an angle of about 30° to 2. 20% of cases within skin disease to each other (either vertical X-ray beam bisects the open each other (either vertical X-ray beam bisects the open 3. Everyday occurrence Scutiform cartilage mouth or the hard palate is vertical and the beam is mouth or the hard palate is vertical and the beam is slightly Not part of the ear canal - within muscles rostro medial slightly angled angled Microbiology: to canal - provides additional support It is often necessary to acquire several exposures with It is often necessary to acquire several exposures with the Normal commensals found on outer ear in dogs and cats: the head in slightly different positions before an optimal head in slightly different positions before an optimal Initially Staphylococcal colonisation of skin or ears radiograph is obtained radiograph is obtained Then recognised as Malassezia pachydermatis yeast: 1. Non lipid dependant 2. Broad based budding organisms Review the gross anatomy of the skull with respect to the ears Review the cranial nerves which supply the inner ear Both these organisms may increase secondary to primary ear disease Temporal bones : Vestibulocochlear (VIII) nerve : Associated structures: Adjacent structures: 1. Responsible for transmitting sensory information from inner ear to brain Cytology: Simple squamous to cuboidal epithelial lining: Each side of skull, contribute to cranial aspect of temporal fossa Taken with cotton bud 1. Pharyngeal mucosal origin Nerves: Temporal bones house : Cochlear branch : Rolled onto slide and heat fixed 2. Secretory goblet cells 1. Facial nerve 1. External acoustic meatus Facial canal in petrosal temporal bone 2. Carries auditory information from cochlea to brainstem and auditory cortex Stained with DIFF quick or Rapid stain Auditory tube Exposed in dorsal cavity 2. Opening to ear canal, leading to middle ear Examined under x400 - 1000 magnification 1. Eustachian tube Exits stylomastoid foramen 3. Located on lateral aspect of temporal bone Vestibular branch : 2. Runs dorsolateral and ventromedial to nasopharynx Additional structures Integument covering 3. Carries information related to balance and spatial orientation from 3. Pseudostratified, ciliated and columnar epithelium = density increases towards Topographical course of CN7: Tympanic bulla : vestibular apparatus to brainstem and cerebellum Parotid salivary gland Skin lines ear canal: nasopharynx Enters petrous temporal bone through internal acoustic meatus (1) 4. Scattered goblet cells: Runs inside facial canal 1. Bulbous bony structure ventral to external acoustic meatus 4. Role in maintaining posture, coordination, and equilibrium Blood vessels: Tightly adherent on concave pinna 1. Auricular artery Henri's pocket on caudal pinnal edge I. More prominent at tympanic cavity end Intermediate component: 2. Houses middle ear structures including ossicles (malleus, incus, and 2. Superficial temporal arteries II. Lecithin, lipids, mucopolysaccharides - surfactant secretion to keep tube patent 1. Enters tympanic cavity near oval window stapes) and the tympanic membrane 3. Branches of external carotid artery Epidermis: 2. Fibres branch of the greater petrosal bone, the stapedial nerve and the Which nerves run in the vicinity of the inner and middle ear? 4. External maxillary vein Thin chorda tympani nerve Internal acoustic meatus : Stratified squamous keratinising epidermis (over tympanic membrane) 1. Bony canal located on petrous part of temporal bone Facial (CN VII) nerve : What are the indications for radiography of the tympanic bullae ? Nerves: 1. Facial nerve exits stylomastoid Dermis: 2. Serves as a passageway for facial nerve and vestibulocochlear nerve 5. Runs in vicinity foramen - passes rostroventral to Thin, contains adnexal structures: DV view : horizontal canal 1. Hair follicles - concave pinna and down ear canal 6. Chorda tympani provides sensation to parts of middle ear ○ Where should your beam be centred ? Stylomastoid foramen : 2. Auriculotemporal branch of mandibular portion of trigeminal Glands: 1. Located on ventral aspect of temporal bone, near junction of petrous and Lateral oblique view : L ear: nerve 5 rostral to vertical canal 1. Sebaceous more prominent distally mastoid part Vestibulocochlear (CN VIII) nerve : ○ The bulla under examination will be placed nearest the plate - in which direction will you rotate the skull to skyline it ? Barley anything visible 2. Apocrine more prominent proximally 2. Serves as an exit point for facial nerve 7. Transmits sensory information from hearing and balance NORMAL Open mouth rostrocaudal view - dogs : 8. Cochlear - carries auditory information from inner ear to brain ○ What structures may obscure the tympanic bullae ? R ear: 9. Vestibular - carries balance and spatial orientation information to brainstem Blue stained - highly ○ What practical considerations need to be made when performing this procedure ? cellular ○ Where do you centre the beam ? 1. Branches of Vagus nerve and facial nerve Abnormal Vagus (CN X) : Form the tympanic nerve It is not easy to obtain an open-mouth view in the cat - what alternative positioning can be used to obtain a symmetrical image Infection confirmed on Traverses cavity - lingual nerve and pre gnanglionic PSNS fibres to 10. Provides sensory innervation to parts of middle ear of both bullae in this species ? microscopy salivary gland Neoplasia, inflammation 2. Post ganglionic fibres of cervical sympathetic trunk Trigeminal (CN V) nerve : Dorsomedial wall of tympanic cavity DV view : Cat runs in dividing septum 11. Provides sensory innervation to external ear canal and skin around ear Joins CN 4 to eye ○ Between horizontal ear canals Lateral oblique view : List the nerves (cranial and others) which might be damaged by disease of the ○ Towards the VD position Connected to nasopharynx middle ear. What clinical signs would you expect to see? Historically, our knowledge of the microbes colonizing the skin and ears has Open mouth rostrocaudal view : been based on bacterial culture and more recently on PCR-based techniques. However, these techniques have limitations – what are they? ○ Mandible, soft tissues of neck can superimpose tympanic bulla Facial (CN VII) nerve : ○ Medical tape used to separate mandible from maxilla or U Shaped device to facilitate positioning, animal should be in dorsal recumbency, head flexed towards thoracic inlet, need to ensure there's no radiodense objects obstructing view 1. Facial nerve passes through middle ear and is particularly vulnerable to damage Malassezia: e.g., sandbags especially in conditions like otitis media (middle ear inflammation) Limited coverage : ○ Vertical primary beam directed rostroventral to caudodorsal and centred immediately ventral to hard palate, base of the 2. Clinical signs include drooping of face, inability to blink, drooling, difficulty tongue eating or drinking 1. Bacterial culture can typically only identify microbes that grow under DV specific laboratory conditions 2. PCR rely on specific primers which may miss less common microorganisms Clinical relevance: Vestibulocochlear (CN VIII) : 3. Damage to middle ear can affect function leading to hearing loss, balance Radiographic changes seen in : Staph and Malassezia Bias and selectivity : disturbances, and vestibular signs such as head tilt, circling, and loss of coordination Otitis media : Severe chronic otitis externa : Neoplasia of ear : 1. Both can be biased towards certain microbes overlooking less abundant ○ Soft tissue opacification ○ Soft tissue swelling ○ Soft tissue mass species or those hard to culture ○ Loss of normal middle ear structures (e.g., ○ Osteolysis - erosion of bony structures ○ Bone destruction (squamous cell carcinoma) Sympathetic nerves : bony landmarks) ○ Tympanic bulla changes - thickened walls, ○ Erosion of cartilage 4. Damage to middle ear can affect sympathetic nerve fibres leading to Horner's ○ Thickening of middle ear soft tissues loss of normal architecture ○ Soft tissue swelling syndrome, characterised by drooping of eyelid (ptosis), constriction of pupil Inability to assess viability : ○ Ossification or mineralisation of soft ○ Calcification of soft tissues ○ Calcification (miosis) and sunken appearance of eye (enophthalmos) tissues ○ Debris or foreign bodies ○ Invasion of adjacent structures 1. Neither method can distinguish between active and inactive cells ○ Narrowing / stenosis of external ear canal Time and cost : MRI and CT Sebaceous glands Apocrine gland 1. Culture-based methods can require weeks, while PCR-based techniques can be costly and require specialised equipment and expertise Cerumen and exudate Tympanic membrane Secretions in ear canal contain: Epithelial structure 1. Exfoliated cells Boundary between external and middle How has our knowledge of the microbial diversity of normal skin and ears 2. Sebaceous secretions that have a high lipid Lateral is stratified squamous keratinising epithelium: changed since the availability of Next-Gen DNA sequencing? content and various classes: 1. Migration of cells centrifugally from middle at level of Lipid content mean is 50% and the range is stratum granulosum 18-93% 2. Normal cleaning mechanism The canine microbiota of clinically affected cases was characterised by an overall 3. Ceruminous gland secretions - more aqueous 3. Upward epithelial migration proceeds distal loss of microbial diversity, high microbial biomass, with overgrowth of certain nature members of the microbiota 4. Immunoglobulins IgA, IgG, IgM = IgG is most Thin lamina propria = collagen bundles predominant Simple squamous or cuboidal mucosal epithelium medially = scattered secretory goblet cells MRI CT These all provide protection and antimicrobial Thicker pars flaccida dorsorostrally - adjacent to edge of malleus The most important microbial taxa enriched in clinically affected ears were layers Thick pars tensa ventrally - larger than pars flaccida and is Malassezia spp, Staphylococcus pseudintermedius, S. schleiferi, and a few translucent in healthy animals anaerobic bacteria such as Finegoldia magna, Peptostreptococcus canis, and Exudate is carried to the surface by epithelial cell Manubrium of malleus visible = C shaped and associated with Porphyromonas cagingivalis migration: collagen in lamina propria Clinical relevance: 1. Cells move laterally from the centre to the tympanic membrane to the periphery The anaerobic microbes here were previously not commonly recognised as What changes can you identify on the 'diseased' T1 MRI ? What abnormalities do you see on this CT, taken from a cat 2. These then desquamate to contribute pathogens in canine ear infections with long term ear disease, affecting the right ear ? production of cerumen What condition(s) is the dog suffering from ? 3. Epithelial migration helps transport cerum to What does this tell you about the diversity of the cutaneous microbiome in superficial portion of ear canal = this removes Fungi had been previously overlooked due to difficulty to culture however NGS the ears of dogs affected by otitis externa compared to healthy dogs? the cerumen and the debris provides technology that facilitates the simultaneous detection and Canine microbiota of clinically affected cases was characterised by an overall quantification of aerobic and anaerobic bacteria and fungi loss of microbial diversity, high microbial biomass, with overgrowth of certain members of microbiota Which organisms are commonly isolated in cases of otitis externa? Thickening of RIGHT horizontal and vertical canal, The most important microbial taxa enriched in clinically affected ears were abnormality of LEFT middle ear Malassezia spp, Staphylococcus pseudintermedius, S. schleiferi, and a few anaerobic bacteria such as Finegoldia magna, Peptostreptococcus canis, and Right otitis externa and left otitis media Porphyromonas cagingivalis Diffuse thickening of R bulla wall and increased opacity within both compartments of bulla Cat has middle ear disease affecting right ear (right The anaerobic microbes here were previously not commonly recognised as otitis media) pathogens in canine ear infections What is dysbiosis? An imbalance of microbial species and a reduction in microbial diversity within