equine larynx

LARYNGEAL DYSFUNCTION:

Dane Tatarniuk, DVMDec. 12, 2012

1. Left Laryngeal Hemiplegia

2. Epiglottic Entrapment

ANATOMY & FUNCTION

Equine Larynx

Anatomy Paired arytenoids Epiglottis Thyroid Cricoid

Equine Larynx

Intrinsic muscles Move laryngeal

cartilages in relation to each other

Cricoarytenoideus dorsalis – abduction of arytenoids & tensing of vocal folds

Thyroarytenoideus, arytenoideus transversus, cricoarytenoideus lateralis – adduction of arytenoids

Equine Larynx

Arytenoid Function Situated on either side of cricoid Composed of hyaline cartilage Cricoarytenoid joint – diarthrodial

Facilitates adduction & abduction movement 3 processes

Corniculate, cuneate & muscular process Arytenoids adduct (close) during swallowing reflex Arytenoids abduct (rima glottidis dilates) fully at high-

intensity exercise to maximize airflow Abduction of arytenoid counter-acts increasing negative

inspiratory pressure (which acts to adduct arytenoids) Decreased airflow hypoxemia hypercarbia metabolic

acidosis musculoskeletal fatigue poor performance

Equine Larynx

Epiglottis Anatomy & Function Triangular structure with apex

pointing rostral Attached to thyroid via

thyroepiglottic ligament Composed of elastic cartilage Normally situated above soft palate

Soft palate against epiglottic base Scallop appearance laterally Vascular pattern dorsally Flips caudally to cover rima glottis

during swallowing

CASE #1

Case #1- Signalment

7 years old Gelding Canadian Warmblood Discipline: Eventing

Case #1 - History

Tiring with exercise 6 month history

Noise Less of a concern

Evaluation by rDVM Standing endoscopy Laryngeal paralysis Referred to UMEC

Case #1 – Diagnostics

Normal vital parameters

Resting endoscopy, standing, un-sedated

Left laryngeal hemiplegia Grade 4

Recurrent laryngeal neuropathy

No other concurrent upper airway abnormalities noted

Left Laryngeal Paralysis

Neurogenic atrophy of intrinsic laryngeal musculature (94% of cases)

Loss of abductor and adductor arytenoid function Cricoarytenoideus dorsalis muscle

Progressive loss of function (not immediate) Other causes:

Perivascular damage from IV injection, guttural pouch mycosis, neck trauma, abscessation of head/neck, neck neoplasms, organophosphate toxicity, plant poisoning, hepatic encephalopathy, lead toxicity, CNS disease

Laryngeal Paralysis Grades

Grade 1 Arytenoid movements synchronous & symmetrical Full adduction attained

Grade 2 Arytenoid movements are asynchronous or

asymmetrical at times Full adduction attained

Grade 3 Arytenoid movements are asynchronous or

asymmetrical Full adduction can not be attained

Grade 4 Complete immobility of arytenoid cartilage

Case #1 - Therapy

Recommendation: Prosthetic Laryngoplasty

“Tie Back” Prosthesis between arytenoid and cricoid Create abduction Provide adequate airflow but not allow aspiration

+/- ventriculectomy via laryngotomy Eliminate noise, further stabilize airway Can be used as sole procedure in draft horses

+/- ventriculocordectomy via standing laser endoscopy 2 cm crescent wedge of tissue removed from leading

edge of vocal fold

Case #1 - Therapy

Pre-operative medication Potassium penicillin, 22,000iu/kg, IV Gentamicin, 6.6mg/kg, IV Phenylbutazone, 4.4mg/kg, IV Tetanus toxoid, IM

General anesthesia Small endotracheal tube Left lateral recumbancy Neck extended IV catheter low in left jugular vein or on right side 5L fluid bag under proximal neck

Help extend throatlatch upwards

Case #1 - Therapy

Surgery ~10cm cranial-caudal incision, cranial extent

starting at left ramus of mandible Ventral and parallel to lingual-facial vein Blunt dissect lingual-facial vein from

omohyoideus muscle Avoid pertinent nerves and vasculature

Dissect between sternocephalicus and cricothyroideus muscles

Follow plane of dissection under lingual-facial vein until expose larynx & associated laryngeal musculature

Case #1 - Therapy

Palpate caudal aspect of cricoid cartilage & muscular process of left arytenoid cartilage

Assistant retracts upwards Suture

#5 Ethibond (Polyester) Alternatives: Stainless steel wire,

nylon, polyethylene Pass suture through cricoid cartilage

(x 2) Walk needle off caudal aspect of

cricoid Stay axial to dorsal sagittal ridge ‘Notch’ of cricoid cartilage Auer &

Stick

Case #1 - Therapy

Intra-operative endoscopic exam Ensure suture does not penetrate laryngeal

mucosa Tunnel leading edges of suture

Under cricopharyngeus muscle Pass suture in caudal-medial to cranial-lateral

direction through muscular process (x2) Engage spine, not tip, of muscular process

Tie cranial suture strand to caudal strand (x2) Assess abduction of left arytenoid with

endoscope Curvature of corniculate cartilage comes into

contact with pharyngeal wall Close musculature & skin routinely

Stent bandage

Auer & Stick

Case #1 – Post Op Care

Post operative medication Potassium penicillin, 22,000iu/kg, IV, QID, 3

days Gentamicin, 6.6mg/kg, IV, SID, 3 days Phenylbutazone, 2.2mg/kg, PO, BID, 5 days Trimethoprim sulfa, 15mg/kg, PO, BID, 5 days

Fed on the ground Exercise

4 weeks of stall rest then 2 weeks of small paddock

Return to exercise at 6 to 8 weeks post-op

Case #1 – Recheck Endoscopy

24 hour recheck endoscopy Maintained abducted

position Estimate 60 to 70% of

rima glottidis area attained

4 week follow up Horse doing well

Prognosis

Success depends on use of horse and measurement of success

Between 50% to 70% of horses have improved performance following laryngoplasty surgery

Success better in horses not intended to race

Decreased noise production not a measure of improved airway function

Complications

Complications decrease prognosis Dysphagia Bilateral nasal discharge

Feed, water, saliva Aspiration pneumonia Chronic coughing Incisional infection Prosthesis failure Chondritis

CASE #2

Case #2 - Signalment

11 years old Gelding Quarter Horse Discipline: Mounted

shooting

Case #2 - History

History of intermittent coughing Severe coughing fit while at show Difficulty eating No performance issues Attended by rDVM

Case #2 – rDVM Diagnostics

Oral exam: normal Head radiographs: normal Endoscopy:

Epiglottic entrapment Severe thickening and necrotic ulceration of

aryepiglottic tissue Intermittent dorsal displacement of soft

palate Small ulcer present on the left rim of soft

palate

Case #2 – rDVM Endoscopy

Case #2 – rDVM Therapy

Procaine Penicillin 22,000iu/kg IM BID Flunixin Meglumine 1.1mg/kg PO SID

Recheck Endoscopy by rDVM: At 7 days - continued entrapment with

intermittent soft palate displacement; improvement of the ulcer

At 14 days - continued healing of ulcers, intermittent soft palate displacement, periodic ventral pharyngeal collapse

Case #2 – Referral Presentation After 14 days medical therapy,

Improvement in ulcer Epiglottic entrapment persists

Case referred for further management

Initial endoscopy: Confirm epiglottic entrapment with mild ulceration Ulceration less compared to previous exam

images Ventral aryepiglottic tissue normal with no

ulceration No adhesions present between epiglottis and

aryepiglottic tissue

Case #2 - Initial Endoscopy

Epiglottic Entrapment

Loose aryepiglottic folds & subepiglottic mucosa displace dorsally above the epiglottis

Exercise intolerance main complaint usually Less commonly coughing, nasal exudate

Prevalence 0.9% in Thoroughbreds Can be induced by

Epiglottic hypoplasia Aryepiglottic fold inflammation / swelling

Chronic cases Thickened, fibrous tissue 45% have ulceration present

Case #2 - Assessment

Recommendation: Surgery Entrapment unlikely to resolve without

intervention Techniques:

Standing vs. general anesthesia Laser axial transection Sharp axial transection

Determined to post-pone surgical management Additional 7 days

Allow ulcer to heal further prior to surgery Decrease risk of adhesion, granuloma

formation

Case #2 – Interim

Medical therapy Procaine Penicillin, 22,000iu/kg, IM, BID, 7

days Flunixin Meglumine, 0.55mg/kg, PO, BID, 3

days Throat Spray, 10cc, PO, SID, 7 days

Glycerin 9cc Dimethyl sulfoxide 1cc

Surgical Techniques

Sharp axial division of aryepiglottic tissue Curved bistoury knife passed nasally and

applied under endoscopic guidance Scalpel transection through laryngotomy or

pharyngotomy Axial division allows membrane to retract

and heal in normal sub-epiglottic position Tissue sparing, minimize scar tissue

If thickened or ulcerated Can consider taking out triangular wedge

segments of aryepiglottic tissue instead of axial division

Surgical Techniques

Laser axial division of aryepiglottic tissue Contact vs. non-contact Tip of laser applied to caudal aspect of

tissue (on midline) and moved rostrally 10 to 12 watts Continue dissection until elastic property of

aryepiglottic tissue causes entrapping membrane to retract below epiglottis

Care to not cause collateral damage to epiglottis, soft palate or pharynx

Case #2 – Surgery

Surgical management 7 days following initial UMEC exam 21 days following initial rDVM exam

Pre-operative medication Detomidine, 0.02mg/kg, IV, given to effect Intranasal lidocaine, 100cc Procaine Penicillin, 22,000iu/kg, IM Gentamicin, 6mg/kg, IV Phenylbutazone, 4.4mg/kg, IV

Case #2 - Surgery

Standing axial excision of aryepiglottic tissue using diode contact laser

Case #2 - Surgery

Rostral edge of epiglottis appears hypoplastic Blunted prominence

Residual thickening of aryepiglottic tissue present on left edge of epiglottis Contract with time Require transection at

future date

Case #2 – Post Op Care

Phenylbutazone, 2.2mg/kg, PO, BID, 5 days Procaine Penicillin, 22,000iu/kg, IM, BID, 3

days Throat Spray, 10cc, PO, SID, 7 days

Glycerin 7.7cc Dimethyl sulfoxide 0.8cc Dexamethasone 1.5cc

Recheck endoscopy 24 hours later Confirmed epiglottis free

Discharged 24 hours after surgery

Case #2 – Recheck

Recheck endoscopy 6 days post-surgery Swelling decreased

considerably Some residual

inflammation present

Prognosis

Reported re-entrapment rate is 5 to 15% with curved bistoury

Reported re-entrapment rate is 4% with laser axial division

Between 10 to 15% of cases develop DDSP following un-entrapment

Complications reduce prognosis: Thermal trauma to epiglottis, soft palate Lacerations to epiglottis, soft palate Cicatrix

REVIEW

Review: Laser

Types: Neo-dymium : yttrium aluminum garnet (Nd:YAG) Gallium aluminum arsinate diode

Quartz or silica fiber-optics to conduct laser energy Human safety - wear protective eyewear

Specific to wavelength of laser – avoid ocular injury Smoke plume

Xylene, toluene – can be toxic If considerable amount produced consider smoke evacuator

Laser energy converted to thermal energy when contacting tissue Incise, coagulate, vaporize Wavelength used influences amount absorbed, scattered,

reflected, transmitted

Review: Laser

Precision incision Smaller fiber (400–600μm) Small contact area, high power density Direct contact with tissue 10 to 15 watts power

Non-specific tissue ablation Larger fiber (800–1000μm) Less specific, do not require direct contact Up to 50 watts power Can coagulate tissue 5mm deep Capable with Nd:YAG, not capable with diode

Review: Recent Literature

Dart, 2009. “Effect of Prosthesis Number and Position on Rima Glottidis Area in Equine Laryngeal Specimens.” Placed dorsal suture and lateral suture

dorsally in the cricoid & through the rostral and proximal muscular process

1.5 cm lateral to the 1st suture & more caudal and distal in the muscular process

When tied independently, no difference in rima glottis area 8.51cm2 & 8.46cm2

When both sutures were tied together, mean area was greater than when either suture was tied alone 9.31cm2


Rakesh, 2008. “Implications of different degrees of arytenoid cartilage abduction on equine upper airway characteristics”. Used computational fluid dynamics modeling to

measure the effects of different degrees of abduction Tested abduction at 100%, 88% & 75% cross

sectional area of rima glottis 88% cross sectional area optimal

less reduction in airflow less collapsing pressure less stress on the repair


Aitken, 2011. “Epiglottic abnormalities in mature non-racehorses: 23 cases.” 8+ years, non race-horses Primary complaint

70% chronic cough 13% nasal discharge Racehorses – exercise intolerance

57% epiglottic entrapment All chronic: thick, ulcerated, and blunted epiglottis

74% resolution of symptoms with appropriate management 24% prolonged medical management (therapy >2 weeks) due to

post-surgical epiglottic inflammation 9% developed DDSP post-epiglottic surgery


Lacourt, 2011. “Treatment of Epiglottic Entrapment by Trans-nasal Axial Division in Standing Sedated Horses Using a Shielded Hook Bistoury.” Reviewed 33 cases using conventional bistoury technique

2 – laceration of soft palate 2 – laceration of epiglottis

Shield hook in 8 standardbreds Minimize damage to soft palate, epiglottis

Mean surgical time = 83 seconds 6 resolution with one incision 2 resolution with two incisions

Inexpensive Faster Authors opinion: technically easier

References

Aitken, 2011. “Epiglottic abnormalities in mature non-racehorses: 23 cases.” JAVMA 238: 12, 1634 – 1638.

Dart, 2009. “Effect of Prosthesis Number and Position on Rima Glottidis Area in Equine Laryngeal Specimens.” Vet Surg 38: 452 – 456.

Lacourt, 2011. “Treatment of Epiglottic Entrapment by Trans-nasal Axial Division in Standing Sedated Horses Using a Shielded Hook Bistoury.” Vet Surg 40: 299 – 304.

Fulton I: Larynx, in Auer JA, Stick JA (eds): Equine Surgery (ed 4). Philadelphia, PA, WB Saunders, 2006, pp 592 – 623.

Palmer SE. “The use of lasers for treatment of upper respiratory tract disorders” Vet Clin Equine (2003) 19: p245 – 263.

Rakesh, 2008. “Implications of different degrees of arytenoid cartilage abduction on equine upper airway characteristics”. EVJ 40 (7), 629 – 635.

equine larynx

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