Veterinary Anatomy: Larynx and Bronchial Collapse

Small Animal Surgical Respiratory Diseases

• Presents a discussion of small animal surgical respiratory diseases, including tracheal collapse, brachycephalic obstructive airway syndrome (BOAS), and laryngeal paralysis.
• The learning objectives focus on describing anatomy and pathophysiology, diagnosing specific conditions, formulating treatment plans, educating clients, understanding surgical options, and assessing prognosis.
• Tracheal collapse is a progressive, irreversible condition where the tracheal width-to-height ratio deviates from 1:1. Laxity of the trachealis muscle progresses, leading to weakness in cartilage rings and possible lumen obliteration. Collapse typically occurs in a dorsoventral direction.
• Pathophysiology includes water loss due to the reduction of glycoproteins and glycosaminoglycans, resulting in cartilage rigidity loss. Coughing can also lead to inflammation, squamous metaplasia of the epithelium, and increased mucous secretion, contributing to the condition.
• Signalment often involves toy and small breed dogs (Yorkies, mini poodles, Pomeranians, Chihuahuas) of middle age.
• Clinical signs associated with respiratory issues include coughing (a "goose honk" sound), episodic dyspnea, exercise intolerance, cyanosis, and syncope, all often exacerbated by palpation.
• Normal respiration involves the expansion of the chest by respiratory muscles, negative pressure within the chest, thoracic expansion, and cervical region compression.
• Extrathoracic trachea collapse occurs during inhalation while intrathoracic trachea collapses during exhalation.
• Pomeranians have a higher incidence of bronchial collapse (up to 83%). Surgical treatment for bronchial collapse is not possible.
• Medical management includes acute oxygen therapy, sedatives, cough suppressants, short-acting corticosteroids, anti-inflammatory doses, bronchodilators.
• Chronic management strategies include controlled exercise (especially when hot), weight loss, and modifications for the environment (avoiding smoke, scented candles, and other irritants), and using a harness instead of a collar for extra support.
• Medications include cough suppressants, sedatives, bronchodilators, corticosteroids, and antibiotics (if a respiratory infection is suspected).
• Medical management is successful in 71% of cases for over a year, possibly eliminating surgical intervention in some cases. Surgery might fail, or the patient may require ongoing medical support.
• Surgical procedures can address the extra-luminal tracheal rings. These treatments do not address possible bronchial collapse, but there is an 75-85% success rate and offer immediate improvement post-operatively. Complications (10-30% of dogs) can occur. Examples are laryngeal paralysis, tracheal necrosis, and pneumothorax.
• Intraluminal tracheal stents treat the entire trachea, but do not address bronchial collapse. Intraluminal stents offer an 83-89% success rate for 1 year follow-up. Post-operative care includes cough suppressants, as needed sedatives, tapering doses of corticosteroids, antimicrobials (2 weeks), and regular re-evaluation with radiographs. Complications include stent fractures, granulation tissue, and stent migration.
• Laryngeal paralysis is a complex anatomical condition involving the epiglottis, thyroid cartilage, cricoid cartilage, arytenoid cartilage, and rima glottidis.
• Cats differ from dogs in that their arytenoid cartilages do not have cuneiform or corniculate processes.
• Laryngeal physiology involves assisting swallowing, pulling cranially for epiglottic coverage, and controlling airway resistance, including reducing resistance during inhalation and controlling the tension on vocal cords (for voice production).
• Laryngeal paralysis results in the loss of ability to abduct arytenoids during inhalation. This process is driven by degeneration of the recurrent laryngeal nerves and loss of function of the cricoarytenoideus dorsalis muscle.
• Congenital laryngeal paralysis is often seen in Siberian Huskies, Dalmatians, Rottweilers, Bouvier des Flandres, and Bull Terriers. Clinical signs begin before 1 year of age. Congenital conditions are frequently accompanied by diffuse neurologic disease.
• Acquired laryngeal paralysis is more common in Labradors, Goldens, Saint Bernards, and Irish Setters with a male dominance. The average age of onset for this type of condition is 9 years. Clinical signs can start acutely (or chronically), often from a progression of a previous chronic condition.
• Diagnosis of respiratory diseases often involves complete blood counts, chemical panels, urinalysis, thyroid panels, thoracic radiographs, swallowing and upper airway examinations.
• Emergency management during respiratory distress can include oxygen, cool environment, sedation (like acepromazine or butorphanol), corticosteroids, and possibly intubation or temporary tracheostomy.
• Medical management involves weight loss, exercise restriction, avoidance of stressful situations (like extreme heat), and harness instead of neck collars.
• Surgical procedures include unilateral arytenoid lateralization.
• Post-operative care involves avoiding food and/or water until the morning following surgery. If no signs of gagging or coughing occur upon intake of food/water, try again later. Patients may benefit from meatballs or canned food to initiate a feeding regimen, gradually increasing the intake of food from solids to kibble over 2-4 weeks. Heavy sedation post-operation should be avoided.
• Complications can include aspiration pneumonia (8-21%), lifelong risk of esophageal dysfunctions, consistent coughing/gagging (up to 33%), persistent recurrent respiratory signs (up to 33%), surgical failure, suture breakage, and cartilage breakdown.
• Outcomes after lateralization are generally positive, improvement is seen in 90% of cases and 70% of patients are still alive after 5 years of monitoring.
• Long-term outcomes of acquired laryngeal paralysis show that it is part of a peripheral neuropathy (GOLPP); 31% have accompanying peripheral neurologic signs, like pelvic limb scuffing, ataxia, and hind limb weakness. Most owners attribute to old age or arthritis.
• Brachycephalic obstructive airway syndrome (BOAS) comprises stenotic nares, elongated soft palate, everted laryngeal saccules, and hypoplastic trachea (among others).
• Diagnostic procedures for BOAS often include evaluation of the nares, palate, pharynx, larynx.
• Surgical treatments for BOAS can be useful if the medical treatment is not successful. Anaesthesia is often a higher risk factor, especially if surgery is done at the latter part of the day.
• Complications of BOAS surgery include dyspnea caused by the swelling of the soft palate post-operation.
• Further complications include death due to issues like aspiration pneumonia or failure to recover from anesthesia.

Brachycephalic Obstructive Airway Syndrome (BOAS)

• BOAS causes various upper airway abnormalities causing increased airway resistance. Typical breeds affected are those where the physical characteristics reduce the size of the airway.
• Primary abnormalities of BOAS include stenotic nares, elongated soft palate, everted laryngeal saccules, and hypoplastic trachea.
• There can be additional, secondary abnormalities to account for.
• There are multiple methods of treating BOAS, some of which might differ depending on which symptoms are prominent.

Other findings in BOAS

• Additional signs of abnormalities other than those listed can also be present
• Abnormal nasal conchae or everted tonsils can be seen in BOAS.