Equine Upper Airway Obstruction Flashcards

1
Q

where does most of the airway resistance come from in the equine airway

A

80-90% in upper airway

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2
Q

why are horses obligate nasal breathers

A

the soft palate is tightly opposed to the base of the larynx so there is no communication between the oropharynx and the nasopharynx

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3
Q

what are the cartilages that make up the equine larynx

A
  1. cricoid
  2. thyroid
  3. epiglottic
  4. paired arytenoid cartilages
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4
Q

label the cartilages of the equine larynx

A
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5
Q

what is each arytenoid cartilage composed of

A

two distinct processes

  1. corniculate process
  2. muscular process
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6
Q

what are the processes of the arytenoid cartilages

A
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7
Q

what are the structures of the larynx

A

the visible portions of the arytenoid cartilages are the corniculate processes

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8
Q

what is the function of the arytenoid cartilages during swallowing

A

adduct during swallowing and fully abduct at high intesity exercise

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9
Q

what are the intrinsic muscles of the larynx (6)

A
  1. cricoarytenoideus dorsalis
  2. cricothyroideus
  3. cricoarytenoideus lateralis
  4. vocalis
  5. ventricularis
  6. arytenoideus transversus
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10
Q

label the intrinsic muscles of the larynx

A
  1. cricoarytenoideus dorsalis (blue)
  2. cricothyroideus (red)
  3. cricoarytenoideus lateralis (orange)
  4. vocalis (yellow)
  5. ventricularis (green)
  6. arytenoideus transversus (purple)
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11
Q

what is the function of the cricoarytenoideus dorsalis muscle

A

abducts the arytenoids and tenses the vocal cords

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12
Q

what nerve innervates the cricoarytenoideus dorsalis muscle

A

recurrent laryngeal nerve

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13
Q

what is the hyoid apparatus composed of

A
  1. paired stylohyoid bones
  2. certahyoid bone
  3. thyrohyoid bones
  4. central basihyoid bone (which has lingual process)
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14
Q

label the structures of the hyoid apparatus

A
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15
Q

where does the epihyoid sit

A

at junction between the ceratohyoid and stylohyoid and is fused with the stylohyoid

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16
Q

what is the function of the hyoid apparatus

A

connects to the skull at the temporohyoid joint

this joint is where the paired largest bones in the hyoid apparatus (stylohyoid bones) articulate with the base of the skull

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17
Q

what are the functions of the muscles that attach to the hyoid apparatus

A

contraction of these muscles atler the shape and position of the apparatus which changes position and shape of the larynx and pharyx

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18
Q

what are the muscles of the hyoid apparatus

A
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19
Q

what are the extrinsic muscles of the larynx (8)

A
  1. hyoglossus
  2. genioglossus
  3. geniohyoideus
  4. muscles of tongue
  5. omohyoideus
  6. sternohyoideus
  7. sternothyroideus
  8. thyrohyoideus
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20
Q

what do the extrinsic muscles of the larynx attach to

A

onto the basihyoid bone, the lingual process of the basihyoid bone, the soft palate and pharynx

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21
Q

what is the function of the extrinsic muscles of the larynx

A

protracts (brings forward) and depresses the tongue as well as pulls the basihyoid bone rostrally which helps increase nasopharyngeal airway size and helps stabilize the walls of the nasopharynx

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22
Q

what are the extrinsic larynx muscles shown

A

hyoglossus (green)

genioglossus (pink)

geniohyoideus (yellow)

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23
Q

where do the omohyoideus, sternoihyoideus and sternothyroideus attach to

A

a group of muscles in the neck (accessory resp muscles) attach onto the caudal aspect of the thyroid cartilage, the basihyoid bone and the lingual process of the hyoid apparatus

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24
Q

what is the function of the omohyoideus, sternohyoideus and sternothyroideus muscles

A

contraction results in caudal traction of the hyoid apparatus and larynx –> dilation and stabilization of the nasopharynx

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25
Q

label the extrinsic laryngeal muscles

A
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26
Q

where does the thyroihyoideus muscle attach to

A

lateral surface of the thyroid cartilage and inserts on the thyrohyoid bone

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27
Q

what does contraction of the thyrohyoideus muscle result in

A

moves the hyoid apparatus caudally or the larynx rostrally and dorsally

helps maintain tight apposition between the soft palate and larynx –> maintains the soft palate ventral to the epiglottis

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28
Q

how do the muscles of the tongue and accessory respiratory muscles work together

A

help dilate and stabilze the nasopharynx

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29
Q

what are the clinical signs of upper resp obstructions

A
  1. noise occuring only during inspiration or expiration at exercise
  2. noise occuring during inspiration and expiration only at exercise
  3. noise during inspiration and expiration which is evident at rest
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30
Q

how does stride rate relate to respiratory rate

A

during gallop stride rate and resp rate are coupled

inspiration occurs when the limbs are off the ground (flight phase) and expiration occurs when the limbs strike out

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31
Q

what are the clinical signs of a horse in respiratory distress (6)

A
  1. loud abnormal resp noises
  2. nasal flaring
  3. reduced nasal airflow
  4. extended and low head position
  5. increased resp rate and effort
  6. cyanotic mucous membranes
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32
Q

what can severe cases of resp distress result in

A

dsyphagia, nasal reflux of food material and/or a cough

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33
Q

what are the steps in evaluating a patient with an abnormal respiratory noise during exercise and showing exercise intolerance

A
  1. patient history
  2. clinical exam
  3. resting upper airway endoscopy
  4. overground endoscopy
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34
Q

what are some questions you could ask when getting a concise patient history

A
  1. what is the intended use
  2. c/s: what are they? when do they occur? at rest or only during exercise?
  3. does the positioning of the head during work have any influence on the noise
  4. has the horse had upper resp surgery, or any prev trauma to the neck or upper resp tract
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35
Q

what are important steps in the clinical exam

A
  1. carefully auscultate the heart and lungs to rule out CVS disease and lower resp disease as a cause of poor performance
  2. palpate throat latch region and neck carefully to assess for signs of prev surgery, trauma and/or jugular vein thrombosis
  3. airflow out of both nostrils and note the colour of nasal discharge
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36
Q

what can resting airway endoscopy diagnose

A
  1. subepiglottic cyst
  2. foreign body
  3. arytenoid chondritis
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37
Q

is this a normal upper airway on resting endoscopy

A

yes

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38
Q

what is recurrent laryngeal neuropathy (RLN)

A

inability to fully abduct the corniculate process of arytenoid cartilage most often the left side

results in inspiratory obstruction of the upper airway

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39
Q

what does progressive loss of large myleinated fibres of the recurrent laryngeal nerve cause

A

neurogenic atrophy of muscles of abduction especially the cricoarytenoideus dorsalis muscle (CAD)

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40
Q

what is shown here

A

atrophy of the left cricoarytenoideus dorsalis muscle (CAD)

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41
Q

how does recurrent laryngeal neuropathy (RLN) cause exercise intolerance (6)

A
  1. progressive loss of myelinated axons of the recurrent laryngeal nerve
  2. paralysis of CAD muscle
  3. inability to achieve max abduction of left arytenoid during exercise
  4. rima glottis progressively reduces in size
  5. hypoxemia, hypercarbia, metabolic acidosis
  6. early fatigue and poor performance
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42
Q

what causes recurrent laryngeal neuropathy (RLN) (5)

A
  1. most cases are idiopathic and involve large breed horses
  2. may be genetic
  3. trauma to recurrent laryngeal nerve (perivascular jugular vein injection of an irritant substance such as phenylbutazone)
  4. organophosphate toxicity
  5. hepatic encephalopathy (disfunction of both arytenoid cartilages)
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43
Q

how is recurrent laryngeal neuropathy (RLN) diagnosed with history

A

inspiratory whistling during exercise with variable degree of exercise intolerance (“roaring”)

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44
Q

what should you do in a clinical exam to assess recurrent laryngeal neuropathy (RLN)

A
  1. auscultate heart and lungs to rule out CVS
  2. palpate throat-latch region and neck to assess for signs of prev surgery, trauma and/or jugular vein thrombosis
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45
Q

how is recurrent laryngeal neuropathy (RLN) graded during resting endoscopy

A

degree of abduction that can be achieved with stimulation of the larynx (swallowing)

four point system

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46
Q

what is grade 1 recurrent laryngeal neuropathy (RLN)

A

full and synchronous abduction of the arytenoid cartilages during resting upper airway endoscopy

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47
Q

what is grade 2 recurrent laryngeal neuropathy (RLN)

A

asynchronous movement of arytenoid cartilages but abduction is achieved with stiumlation of larynx

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48
Q

what is grade 3 recurrent laryngeal neuropathy (RLN)

A

asynchronous movement of arytenoid cartilages and full abduction cannot be achieved with stimulation of the larynx

ex. there is still movement in the left corniculate process of the arytenoid cartilage, but it is asynchronous with the right and full abduction cannot be achieved

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49
Q

what is grade 4 recurrent laryngeal neuropathy (RLN)

A

there is complete immobility of the affected arytenoid cartilage and vocal fold

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50
Q

can treatment decisions for recurrent laryngeal neuropathy (RLN) be made based soley on findings during resting endoscopy

A

ideally no

resting doesn’t replicate the function of the larynx during exercise and arytenoid function may change with the intro of exercise

overground is best way to assess upper airway dynamics and should be used in conjunction with resting endoscopy

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51
Q

how is recurrent laryngeal neuropathy (RLN) graded in overground endoscopy

A

four point

the degree of arytenoid abduction observed during resting endoscopy doesn’t correlate with the degree of arytenoid abduciton during exercise

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52
Q

what does grade A of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like

A

full abduction of the arytenoid cartilages during inspiration

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53
Q

what grade of recurrent laryngeal neuropathy (RLN) during overground endoscopy is this

A

grade A

normal

54
Q

what does grade B of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like

A

there is partial abduction of the affected arytenoid cartilage during inspiration to a position between full abduction and its positing during resting endoscopy

55
Q

what grade of RLN on overground endoscopy is this

A

grade B

56
Q

what does grade C of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like

A

abduction of the affected arytenoid cartilage during inspiration is equivalent to its position during resting endoscopy

57
Q

what grade of RLN on overground endoscopy is this

A

grade C

58
Q

what does grade D of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like

A

collapse of the corniculate process into the contralateral half of the rima glottis during inspiration typically with concurrent vocal fold collapse

59
Q

what grade of RLN is this on overgound endoscopy

A

grade D

60
Q

how do you use resting and overground endoscopy grade systems together

A

ex. on resting endoscopy there is grade 4 RLN and on overground endoscopy the grade is D –> overall this horse would be diagnosed with grade 4D RLN when they are combined

61
Q

how is recurrent laryngeal neuropathy (RLN) managed

A

based on presenting complaint (abnormal upper resp noise, poor perfromance or both)

age

use of the horse

degree of arytenoid abduction during overground endoscopy

62
Q

what is prosthetic laryngoplasty

A

tie-back

placement of nonasorbable suture prosthesis between cricoid cartilage and muscular process of the affected arytenoid cartilage

the prosthesis allows for permanent abduction of the corniculate process of the arytenoid cartilage

63
Q

when should a prosthetic laryngoplasty be recommended as treatment for a horse with RLN

A

reserved for horses in which arytenoid collapse is confirmed with dynamic endoscopy and its having a negative impact on performance

64
Q

what are intraop complications can occur with prosthetic laryngoplasty

A
  1. hemorrhage
  2. needle breakage
  3. perforation of laryngeal or esophageal mucosa
  4. cartilage damage by suture
65
Q

what are post op complications that can occur with prosthetic laryngoplasty

A
  1. seroma formation at surgical site
  2. surgical site infection
  3. incisional dehiscnece
  4. dysphagia
  5. coughing
  6. mild to excessive loss of surgical abduction of arytenoid over time
66
Q

what other conditions can occur with recurrent laryngeal neuropathy (RLN)

A

vocal fold collapse

67
Q

how do the vocal folds collapse with concurrent recurrent laryngeal neuropathy (RLN)

A

when there is loss of CAD muscle function and arytenoid collapse there is decreased tension on associated vocal fold –> predisposing it to collapse during exercise

68
Q

what is occuring here

A

concurrent vocal fold collapse with recurrent laryngeal neuropathy (RLN)

69
Q

how is vocal fold collapse managed surgically

A

surgical removal of affected vocal fold(s) and associated laryngeal saccule(s)

ventriculocordectomy or hobday

70
Q

what does a ventriculocordectomy do

A

stabilize the paralyzed arytenoid cartilage and widen the ventral aspect of the rima glottis and decrease respiratory noise associated with RLN

71
Q

when would a ventriculocordectomy be recommended

A

performed concurrently with tie-back to help maximize airflow dynamics in horses graded C and D on overground endoscopy

or

on its own to reduce abnormal inspiratory noise where the primary owner complaint is noise and arytenoid collapse is mild (grade B)

72
Q

what are post op management changes with ventriculocordectomy or laryngeal palatoplasty

A

when the arytenoid cartilages are permanelty abducted and vocal fold(s) and ventricle(s) surgically removed –> predisposing the patient to aspiration of food content

horses should be fed from the floor permanently post op

73
Q

what is the prognosis following surgical treatment in RLN

A

50-70% of racehorses have improved performance after sugery

75-90% involved in non-racing activities have imrpoved performance after surgery

74
Q

how does reinnervation of the CAD muscle work

A

isolating the first or second cervical nerve branches (C1/C2) which innervate the omohyoideus muscle and implanting them into the affected CAD muscle to promote reinnervation and hopefully returning muscle function

75
Q

how long does it take to see success after reinnervation of CAD muscle

A

4-5 months but in some cases 12 months

76
Q

when would reinnervation of CAD muscle be recommended

A

younger horses with grade B and C laryngeal movements are the best candidates as there is less atrophy than with horses grade D

not suitable for horses that need a quick return to atheletic performance

77
Q

what are the complications of CAD reinnervation surgery

A

few complications

most common is seroma formation and incisional infection

78
Q

what is the prognosis of CAD muscle innervation

A

since its a newer procedures there is little published data

but 80% of racehorses showed evidence of reinnervation but only 45% showed improved performance

79
Q

what is partial arytenoidectomy

A

removal of the corniculate process and body of the arytenoid cartilage

only muscular process of the arytenoid cartilage is left intact

80
Q

when would i recommend a partial arytenoidectomy

A

very invasive with a high post operative complication rate

it shouldn’t be considered as a first-line treatment for RLN

only exception is if there is a congenital malformation of the laryngeal cartilages which would prevent a prosthetic laryngoplasty from being performed

may be recommended for cases in which a prosthetic laryngoplasty has failed due to fracture of laryngeal cartilages, preventing another suture prothesis from being placed

81
Q

what are the complications of partial arytenoidectomy

A
  1. dysphagia occurs in up to 36% of horses
  2. edema and hematoma formation at surgical site –> dyspnea (temporary tracheostomy)
  3. long term coughing esp while eating
82
Q

what is the prognosis of a partial arytenoidectomy

A

60-78% of racehorses return to racing

75% of non-racehorses return to their prev level of use

83
Q

what is dorsal displacement of soft palate (DDSP)

A

displacement of the caudal free borded of the soft palate dorsal to the epiglottis

84
Q

what are the two types of dorsal displacement of soft palate (DDSP)

A
  1. intermittent
  2. persistent
85
Q

what is intermittent dorsal displacement of soft palate (DDSP)

A

more common

occuring only during exercise

86
Q

what is persistent dorsal displacement of soft palate (DDSP)

A

rare

observed in resting horses

likely due to neurologic damage secondary to guttural pouch disease or neoplasia

87
Q

what does intermittent dorsal displacement of soft palate (DDSP) result in

A

expiratory airway obstruction

88
Q

when is intermittent dorsal displacement of soft palate (DDSP) more commonly seen

A

in 2-3 year old thoroughbred and standard bred racehorses

as well as sport horses exercised with their head and neck in flexed position

89
Q

how does intermittent dorsal displacement of soft palate (DDSP) impair performance (4)

A
  1. flow limiting expiratory obstruction
  2. increased tracheal expiratory pressure and impedance
  3. reduced minute ventilation
  4. hypoxia, hypercarbia, impaired athletic performance
90
Q

how does a flexed head position result in intermittent dorsal displacement of soft palate (iDDSP) (5)

A
  1. head and neck flexion
  2. alteration in upper airway dimensions
  3. increased airway resistance and negative inspiratory pressure
  4. instability of soft palate
  5. increased susceptibility to dorsal displacement of the soft palate
91
Q

what is the pathogenesis of intermittent dorsal displacement of soft palate (iDDSP)

A

unknown

50% of cases have concurrent lower airway disease and in some cases evidence of upper airway inflammation

can occur with other disease (epiglottic entrapment)

several muscles or nerves where dysfunction could lead to iDDSP

92
Q

how is intermittent dorsal displacement of soft palate (iDDSP) diagnosed with history

A

young performance horses with history of sudden impairement in performance often at max exercise (towards end of race)

gurgling upper resp noise or open mouth breathing

93
Q

what is commonly seen in intermittent dorsal displacement of the soft palate (iDDSP)

A

50% of cases have concurrent lower resp disease

94
Q

when should resting endoscopy be performed in intermittent dorsal displacement of the soft palate (iDDSP)

A

evaluate airway for any gross abnormalities

its likely you wont see intermittent dorsal displacement of the soft palate (iDDSP) during rest

but conditions such as persistent DDSP can be diagnosed with resting endoscopy

95
Q

what are the conservative treatments of intermittent dorsal displacement of the soft palate (iDDSP)

A
  1. rest from exercise and admin of systemic anti-inflammatories (NSAIDs) if upper airway inflammation present
  2. rest from exercise and treatment of lower airway disease if present
  3. improve physical condition
  4. tack changes
96
Q

what are surgical managements of intermittent dorsal displacement of the soft palate (iDDSP)

A
  1. palatoplasty
  2. staphylectomy
  3. myectomy
  4. laryngeal tie forward
97
Q

when is conservative management of iDDSP indicated

A

two year old horses are thought to improve spontaneously as they mature

98
Q

what is pharyngeal lymphoid hyperplasia

A

small foci of lymphoid tissue spread diffusely over the roof and lateral walls of the pharynx

enlargement of these islands of tissue

occurs in young horses due to a combo of immune response and exposure to infection

99
Q

how is phrayngeal lymphoid hyperplasia treated

A

rest and admin of systemic NSAIDs

done before resorting to surgery for conditions such as iDDSP

100
Q

what is palatoplasty

A

reduce flaccidity or “tighten” the caudal free border of the soft palate through fibrosis reducing the likelihood of it displacing dorsal to the epiglottis

the soft palate is cauterized with heated steel rods or a diode laser

101
Q

what staphylectomy

A

0.75cm of the caudal free border of the soft palate is surgically removed

102
Q

what is myectomy

A

partial resection of the accessory resp muscles

includes sternohyoideus and sternothyroideus with or without omohyoideus or resection of the insertion of the sternothyroideus alone

103
Q

how does myectomy help iDDSP

A

by resecting the accessory resp muscles

prevent caudal retraction of the larynx helping increase soft palate epiglottis contact and making it harder for the soft palate to flip dirsal to the epiglottis

104
Q

what is laryngeal tie forward

A

replaces the action of the thyrohyoideus muscle bilaterally

which is to advance the larynx rostrally and dorsally

a non-absorbable suture prosthesis is placed between the thyroid cartilage of the larynx and the basihyoid bone of the hyoid apparatus

105
Q

how does a laryngeal tie forward assist in iDDSP

A

advances the larynx 4cm rostrally and dorsally –> increasing soft palate epiglottis contact and making it harder for the soft palate to flip dorsal to the epiglottis

106
Q

what is the prognosis post conservative management in IDDSP

A

53-61%

107
Q

what is the prognosis of palatoplasty in iDDSP

A

28-51%

108
Q

what is prognosis of staphylectomy in iDDSP

A

60%

109
Q

what is prognosis of myectomy in iDDSP

A

58-71%

110
Q

what is the prognosis of laryngeal tie forward

A

80-82% initially

55-65% with recent work

111
Q

what is epiglottic entrapment

A

aryepiglottic folds are bands of mucosa that run from the arytenoid cartilages of the larynx and attach along the free edge of the epiglottis –> the folds become abnormally positioned above the dorsal epiglottic surface and encompass the epiglottis, resulting in epiglottic entrapment

112
Q

what is shown here

A

intermittent dorsal displacement of soft palate during exercise

113
Q

what is shown here

A

pharyngeal lymphoid hyperplasia

114
Q

what is shown here

A

top is palatoplasty with diode laser

bottom palatoplasty with heated steel rods

115
Q

what is shown here

A

laryngeal tie forward

116
Q

what is shown here

A

epiglottic entrapment

the outline of the epiglottis can be seen, the sharp scalloped edges of the epiglottis are not observed

with DDSP you can’t see the epiglottis at all

117
Q

how is epiglottic entrapment treated

A

surgical transection or excision of entrapping treatment

118
Q

what is arytenoid chondropathy

A

progressive inflammatory chondritis of the arytenoid cartilages typically originating from infection

119
Q

what is the most common manifestation of arytenoid chondropathy

A

granuloma formation on axial surface of the arytenoid cartilages

results in abnormal inspiratory noise and exercise intolerance

severe cases it may result in complete upper airway obstruction

120
Q

what is seen here

A

arytenoid chondropathy

granulomas on the axial surface of the left arytenoid cartilage

121
Q

how are arytenoid chondropathy treated

A

early + mild cases: may respond to medical management, including rest as well as topical and systemic anti-inflammatories (systemic NSAIDs, topical corticosteroids) and systemic antibiotics

but most require excision through a partial arytenoidectomy

if both cartilages are involved –> permanent tracheostomy

122
Q

what are the most common location of masses and cysts

A

subepiglottic cysts

123
Q

how are subepiglottic cysts managed

A

surgical excision

124
Q

what other epiglottic masses can there be

A

fungal and bacterial granulomas and neoplasia

125
Q

what is tracheal collapse commonly due to

A

congenital defect in tracheal cartilages in shetland ponies and american mini horses

126
Q

what are the other causes of tracheal collapse

A
  1. paresis of the trachealis muscle,
  2. mineralization of the tracheal cartilages
  3. lower airway disease (bacterial pneumonia, recurrent airway obstruction)
127
Q

what is secondary tracheal collapse due to

A

trauma but is uncommon

128
Q

what are the clinical causes of tracheal collapse

A

intermittent initially and associated with stressful events, exercise and dust, hot weather

over time freq and severity of clinical signs increase

129
Q

what to mild, moderate and severe cases of tracheal collapse present as

A

mild cases have increased resp rate and exercise intolerance

moderate to severe: audible upper resp noise and may show signs of acute resp distress

130
Q

how is tracheal collapse diagnosed

A
  1. history, signalment, clinical exam and resting airway endoscopy
  2. trachea may be localized to one region or significant portion of trachea –> typically collapses along the dorsal membrane in the region where tracheal rings are incomplete
131
Q

how is tracheal collapse treated

A

for cases in acute resp distress –> temporary tracheotomy and oxygen is typically required

not in immediate distress –> restriction of exercise, mangement of environment, and treatment of any concurrent resp disease