Larynx Flashcards
According to DeGroot 2020 in Vet Surg what sedative was associated with maintenance of laryngeal function during sedated airway examination?
Dexmedetomidine did not inhibit laryngeal function (either alone, or in combination with butorphanol or hydromorphone). Propofol led to false positive results.
In a study by Drudi 2022 in Vet Surg, was a greater increase in the rima glottidis area observed following cricoarytenoid lateralization or thyroarytenoid lateralization?
Cricoartytenoid lateralization (200% compared to 150% increase).
A significant reduction in immediate post-operative rima glottidis size was also observed at 15 days post-op in the thyroartytenoid lateralization group.
In a study by Touzet 2022 in VRU, what radiographic ratio was used in the detection of bilateral laryngeal paralysis?
The ratio of maximum ventricular length over length of the third cervical vertebra (MVL/LC3). Bilateral laryngeal paralysis very likely for ratios >0.5, unlikely for ratios <0.3.
In a study by Moser 2022 in JFMS, what was the primary short term complication in cats undergoing partial laryngectomy?
Respiratory distress (temporary tracheostomy required in 2/6 cases).
Lymphoma was the most commonly resected mass.
In a study by Bonanno 2023 in JFMS, what modification of cricoarytenoid lateralization resulted in increased left arytenoid lateralization?
Complete disarticulation of the cricoarytenoid joint. Cadaveric study, so clinical outcomes unknown.
In a study by Mullins 2019 in Vet Surg, what percentage of dogs undergoing epiglottopexy for epiglottic retroversion suffered from failure? In what percentage of cases undergoing either epiglottopexy or epiglottectomy was a major post-operative complication reported? What was the median survival time for all cases?
42% of dogs undergoing either temporary or incisional epiglottopexy suffered from failure.
49% of total cases suffered a major post-operative complication (58.3% temporary epiglottopexy, 54% incisional epiglottopexy, 50% partial epiglottectomy, 17% subtotal epiglottectomy).
MST was not reached at 716 days.
What is depicted in this image of the larynx of a Norwich terrier from a study by Johnson 2021 in JVIM? What is the treatment for this condition?
Norwich terrier upper airway syndrome (thought to be related to a genetic mutation in the gene for the ADAMTS3 metallopeptidase enzyme).
Surgical treatment typically involves ventriculectomy. This study demonstrated good owner assessed outcomes in 81% of dogs, regardless of whether or not surgery was pursued.
In a study by Rishniw 2021 in Vet Surg, did doxepin improve the quality of life in Labradors with laryngeal paralysis? What is the mechanism of action of doxepin?
No improvement in QOL was observed.
Doxepin is a tricyclic antidepressant that primarily inhibits reuptake
of serotonin and norepinephrine.
Name the cartilages of the larynx.
Epiglottic, thyroid, cricoid, sesamoid, interarytenoid, paired arytenoid.
Label the following diagram.
What attaches the epiglottis to the arytenoid cartilages laterally?
The aryepiglottic folds.
Which is the largest laryngeal cartilage?
The thyroid cartilage
What is the attachment of the cricoarytenoideus dorsalis on the arytenoid cartilage called?
The muscular process.
What are the components of the arytenoid cartilages?
Vocal, cuneiform, corniculate, and muscular processes.
What are the extrinsic muscles of the larynx?
Thyropharyngeus and cricopharyngeus. Both innervated by the glossopharyngeal and vagal nerves.
What is the most important intrinsic muscle of the larynx? What is its function?
Cricoarytenoideus dorsalis. Arises from the dorsolateral cricoid and inserts on the muscular process of the arytenoid. Functions to abduct the arytenoid and open the glottis.
What is the innervation to the larynx?
The caudal and cranial laryngeal nerves. The caudal laryngeal nerve (a branch of the recurrent laryngeal) supplies motor innervation to all of the intrinsic muscles of the larynx besides the cricothyroideus muscle).
The cranial laryngeal nerve (originating from the vagus) supplies the cricothyroideus muscle.
What is the blood supply to the larynx?
The cranial and caudal thyroid arteries.
What are the three functions of the larynx?
- Blocking the laryngeal opening during swallowing.
- Controlling airway resistance.
- Voice production
What is the most common laryngeal neoplasia in cats?
Lymphoma
What diagnostics should be performed in the work-up of suspected laryngeal neoplasia?
Laryngeal examination, mass biopsy, thoracic radiographs +/- CT.
Temporary tracheostomy may be required to facilitate work-up.
What are the treatment options for laryngeal neoplasia?
- Radiation or chemotherapy (lymphoma).
- Resection of small benign masses via a transoral or ventral laryngotomy.
- Partial or complete laryngectomy (cordectomy can be performed in tumour confined to the vocal cord).
How can partial laryngectomies be reconstructed?
Sliding of the remaining thyroid cartilage, alternatively if the cricoid is excised the trachea can be advanced cranially and attached to the thyroid.
Large defects can be repaired using free tissue implants (costal cartilage, buccal mucosa) or local muscle flaps (sternohyoideus muscle island flap sparing the cranial thryoid arteries).
How is a total laryngectomy performed?
The skin is incised on midline and the thyropharyngeus, cricopharyngeus, sternothyroideus, and thyrohyoideus muscles are detached from the larynx. The trachea is detached from the cricoid and anastomosed to the skin after passing through the intact sternohyoideus muscles. The larynx is removed.
What are the components of BOAS?
Stenotic nares (43-85%), elongated soft palate (86-96%), redundant pharyngeal folds, hypoplastic trachea (38%), excessive nasopharyngeal turbinates.
Secondary changes include everted laryngeal saccules (55-66%) and laryngeal collapse (8-70%).
Concurrent GI abnormalities also common (esophagitis, gastritis, pyloric mucosal hyperplasia, diffuse inflammation).
What are the stages of laryngeal collapse?
Stage 1: laryngeal saccule eversion.
Stage 2: medial displacement of the cuneiform cartilage.
Stage 3: collapse of the corniculate processes and loss of the dorsal arch of the rima glottidis.
What is the treatment for laryngeal collapse?
Correction of primary abnormalities (stenotic nares, elongated soft palate).
Laryngeal sacculectomy +/- laryngeal tie-back or permanent tracheostomy.
What are some complications associated with laryngeal sacculectomy?
Recurrence, laryngeal webbing, proliferative soft tissue formation.
What medical management strategies can be useful for control of clinical signs related to laryngeal collapse?
Weight loss, exercise restriction, glucocorticoids, furosemide +/- prokinetic and antacid medication.
What are potential causes of laryngeal paralysis?
Anything that damages the vagal nerve or its branches (recurrent laryngeal or caudal laryngeal) which supply the cricoarytenoideus dorsalis muscle, or damage to the CAD itself.
Are males or females more likely to be affected by laryngeal paralysis?
Males 2-3 times more likely.
Which breeds are most commonly affected by congenital laryngeal paralysis? What is the cause?
Dalmatians and Huskies.
Thought to be due to progressive degeneration of neurons within the nucleus ambiguus and wallerian degeneration of the laryngeal nerves.
Clinical signs normally start before 1 year of age and prognosis is guarded to poor.
In which breeds are acquired laryngeal paralysis most commonly reported?
Labrador, golden retrievers, saint bernards, irish setters.
What are some causes of acquired laryngeal paralysis?
Infectious, chronic endocrine (hypoT), immune mediated-polyneuropathy, surgical damage to the vagus or recurrent laryngeal nerves, OP toxicity, retropharyngeal infection, rabies, tick paralysis, neoplasia, laryngeal myopathy, cervical trauma, cranial mediastinal mass, PDA ligation (reported in a cat).
Most commonly is considered idiopathic (may be early clinical presentation of more generalized polyneuropathy).
What are the most common clinical signs associated with acquired laryngeal paralysis in dogs and cats?
Dogs: change in voice, coughing gagging, progressing to stridor and exercise intolerance.
Cats: dyspnea, tachypnea.
What laboratory findings are common in cases of acquired laryngeal paralysis?
CBC, biochem often normal, although leukocytosis may be observed with secondary aspiration pneumonia.
Heatstroke patients may have more widespread derangements in coagulation parameters, electrolytes, and acid-base metabolism.
Hypercholesterolemia, hyperlipidemia, and liver enzymopathy may suggest hypoT. Can be confirmed by T4 and TSH testing.
Acetylcholine receptor antibody titers should be measured if myasthenia gravis is suspected.
What imaging techniques can be used for work-up of acquired laryngeal paralysis?
Radiography to investigate for other causes of dyspnea, aspiration pneumonia and megaesophagus.
Esophagram not normally performed due to risk of aspiration.
Ultrasound has been described to assess laryngeal function.
Direct assessment of larynx required to confirm disease.
Electromyography can be used to assess for evidence of CAD denervation in dogs as young as 12-weeks of age.
What is the mechanism of action of doxapram?
Central nervous stimulant that increases tidal volume and respiratory rate (increases electrical activity in the respiratory centers of the medulla).
Can be used to aid in the assessment of laryngeal paralysis.
What emergency medical management is recommended in patients with acute upper airway obstruction secondary to laryngeal paralysis?
Active cooling, intravenous fluids, oxygen supplementation, sedation (acepromazine), dexmethasone +/- diuretics (if evidence of obstructive pulmonary edema).
Temporary tracheostomy may be required.
What surgical options are available for treatment of laryngeal paralysis?
- Unilateral cricoarytenoid lateralization.
- Unilateral thyroarytenoid lateralization.
- Transoral partial laryngectomy.
- Ventral laryngotomy for partial laryngectomy.
- Castellated laryngofissure.
- Permanent tracheostomy
Describe the surgical approach for unilateral cricoarytenoid lateralization.
Does cricoarytenoid or thyroarytenoid lateralization result in greater reductions in airway pressure?
Cricoarytenoid lateralization (increase of 207% of the rima glottidis compared to 140%). However, the relation to degree of clinical improvement has not been shown. Thyroarytenoid lateralization may be faster to perform.
Why is excessive lateralization of the arytenoid during cricoarytenoid lateralization not recommended?
It will result in a segment of the rima glottidis not being covered by the epiglottis, increasing the risk of aspiration during swallowing.
What are some complications associated with cricoarytenoid lateralization surgery?
Seroma, intramural hematoma, aspiration pneumonia, persistent coughing or gagging, persistent or recurrent respiratory signs (more common in small breed dogs), residual stridor on auscultation, surgical failure from suture breakage or arytenoid cartilage fragmentation, laryngeal webbing, gastric dilatation and volvulus, and progression of generalized neurologic signs.
What are some factors associated with an increased risk of complications following cricoarytenoid lateralization surgery
Megaesophagus (also associated with an increased risk of death), preoperative pneumonia, temporary tracheostomy.
What is the complication rate after bilateral cricoarytenoid lateralization surgery?
89%. Bilateral thyroarytenoid lateralization may have less complications (12-33%), but has a high rate of recurrence of clinical signs.
What was the complication rate after cricoarytenoid lateralization surgery in cats?
50%
What percentage of dogs were still alive at 5 years after cricoarytenoid lateralization surgery?
70% (90% showed improvement in signs post-operative).
What is transoral partial laryngectomy?
Unilateral or bilateral removal of the vocal cords, resection of the corniculate and vocal processes of the arytenoid.
In what percentage of dogs are complications reported following partial transoral laryngectomy for laryngeal paralysis?
40-50%; including aspiration pneumonia (6-33%), persistent cough, vomiting, respiratory stridor, exercise intolerance. A second surgery is required in 18% of dogs due to persistence of clinical signs.
Laryngeal webbing is a potentially severe complication of this surgery, most likely to occur when bilateral vocal fold resection is performed.
What medications can be administered to potentially decrease the risk of laryngeal webbing following partial transoral laryngectomy?
Prednisone, mitomycin C.
What are the benefits of a ventral approach for partial laryngectomy over a transoral approach for treatment of laryngeal paralysis?
Allows for more precise dissection and permits primary mucosal closure.
Allows for ventriculocordectomy without disruption to the thyropharyngeus and cricoarytenoideus dorsalis muscles.
What are the main complications associated with partial laryngectomy via a ventral laryngotomy for treatment of laryngeal paralysis?
Aspiration pneumonia and cicatrix formation causing respiratory distress, but seem to be less likely than using the transoral approach and therefore may be preferred.
How is castellated laryngofissure performed?
Offset closure of a step in the thyroid cartilage results in enlargement of the ventral laryngeal ostium.
What are some complications associated with castellated laryngofissure?
Laryngeal bleeding and edema. Often requires placement of a temporary tracheostomy tube for 2-3 days.
Does not reduce airway resistance as effectively as cricoarytenoid lateralization. Because of this (and the difficulties of the procedure/complications), it is rarely performed.
What are some options for devocalization of the dog?
Transoral vocal fold resection or ventral laryngotomy with primary closure.
What is the treatment for feline inflammatory laryngeal masses (obstructive lymphoplasmacytic inflammation and lymphoid hyperplasia)?
Glucocortoids and antibiotics. Must be differentiated from lymphoma with biopsies.
Prognosis is poor if disease is advanced (cause is unknown).
What is the preferred treatment for post-operative laryngeal webbing?
Ventral laryngotomy and web resection/transection and primary mucosal closure.
What is the cause of epiglottic retroversion?
Laxity of the hypoepiglotticus muscle (which pulls the epiglottis ventral to the soft palate during open mouth breathing to open the airway) and extreme inspiratory effort.
What treatments are described for epiglottic retroversion?
Epiglottopexy and partial epiglottectomy.
How is displacement of the glossoepiglottic mucosa treated?
Typically seen in dogs with BOAS, and resolves with treatment of the primary cause of upper airway obstruction.
