Introduction

Brachycephalic obstructive airway syndrome (BOAS) has been well described in the veterinary literature. Brachycephalic dogs have shortened, wide facial features. These compressed facial features are the result of inherited developmental defects in gene regulation and cellular metabolism of bones undergoing membranous ossification that originate from the skull base and neural crest ectoderm during development.^1–3 The primary components and anatomic defects of brachycephalic syndrome include stenotic nares, elongated soft palate, redundant pharyngeal folds, and hypoplastic trachea.^1,2,4–9 Both stenotic nares and elongated soft palate are considered congenital defects within BOAS.²

Common clinical signs associated with BOAS include inspiratory dyspnea, stertor, stridor, snoring, collapse, and cyanosis.^4–6 More recent studies have described a high incidence of gastrointestinal signs in association with BOAS. These clinical signs involving the gastrointestinal tract may include vomiting, dysphagia, esophagitis, gastritis, and duodenitis.^6,10,11

Primary components of BOAS lead to increased airway resistance and negative pressure within the airway and may lead to the progression of other secondarily acquired components. These pathologically induced secondary components include everted laryngeal saccules, everted tonsils, and laryngeal collapse.^4–7,12 Secondary components further complicate and add additional negative pressure, airway turbulence, and may lead to the development of laryngeal edema and obstruction.^4–7,12 If severe enough, the increased negative pressure may supersede the resistance of the surrounding tissues and progress to complete laryngeal collapse.¹² BOAS may lead to dyspnea, patient distress, and, ultimately, death if medical and/or surgical intervention is not initiated in the emergency setting.

Obstruction of the larynx and rima glottidis by glossoepiglottic (GE) mucosa has not been described in the literature, and there is limited information describing the involvement, clinical relevance, and surgical correction of the GE mucosa in dogs with BOAS. The authors in this case report describe a rare presentation in which a secondary component of BOAS, severe edema and displacement of the GE mucosa, resulted in near complete obstruction of the rima glottidis and severe dyspnea that required surgical intervention. Additionally, the authors describe a novel surgical technique that describes resection and primary closure of GE mucosa, which resolved this patient's dyspnea.

Case Report

An approximately 22 mo old male neutered English bulldog presented to the Atlantic Coast Veterinary Specialists' emergency service for evaluation of respiratory distress. Prior to presentation, there was no previous history of respiratory problems, known exposure to any toxin, physical activity, or any precipitating stressful event. The patient had previously been diagnosed with gluten food allergies. Current medication included daily glucosamine and chondroitin supplementation for arthritis of the right stifle. The owner pursued medical attention for progressively labored breathing of 2 to 3 hr duration. Initial observation revealed an anxious patient in moderate respiratory distress. On physical exam, a temperature of 38.67°C, heart rate of 136 bpm, and tacky mucus membranes with a capillary refill time <2 sec were noted. Abdominal and peripheral lymph node palpation were within normal limits. Loud stertorous breathing was apparent. No pulmonary crackles were detected on thoracic auscultation, but referred upper airway sounds prevented further detection of more subtle changes. Moderate to severe stenotic nares were noted. A presumptive diagnosis of BOAS was determined based on signalment, physical exam, and clinical signs.

Initial treatment included 2.18 mg (0.1 mg/kg) of butorphanol IV, 50 mg of diphenhydramine (2.3 mg/kg) IM, 4 mg (0.18 mg/kg) dexamethasone sodium phosphate IV, and supplemental oxygen administered with an oxygen mask. Two-view thoracic radiographs were obtained shortly after initial triage. Thoracic radiographic findings revealed a mild, diffuse interstitial pattern. Radiographic interpretation of the trachea was determined to be normal. A complete blood count and chemistry panel were within normal limits.

The patient became more distressed after the thoracic radiographs were completed and was placed in an oxygen cage with 40% oxygen supplementation with close monitoring of respiration rate and breathing pattern. An exaggerated effort was noted on inspiration with open mouth breathing. Cyanosis of the mucous membranes and tongue developed concurrently with severe respiratory distress over the next 15 min with no evidence of any or impending response to sedation or steroid treatment. Oxygen saturation was measured with a pulse-oximeter at 86%. A 20 gauge IV catheter was placed in the left cephalic vein. Propofol (5 mg/kg) was administered to effect for laryngeal examination and intubation.

Upon oropharyngeal examination, complete obstruction of the rima glottidis and epiglottic entrapment were observed. The GE mucosa expanded in volume and displaced dorsally due to the edema that developed within the redundant mucosal tissue. This voluminous and dorsal displacement of the GE mucosa completely obscured the lumen of the glottis (Figure 1) and restricted epiglottic movement. Static displacement of the GE mucosa was maintained throughout inspiration and expiration, which led to sustained obstruction of the rima glottidis and concurrent epiglottic entrapment. Additional abnormalities included elongated soft palate and everted laryngeal saccules (stage 1 laryngeal collapse).⁷

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The edematous GE mucosa was retracted (Figure 2) to allow intubation of the epiglottis and trachea. Oxygen saturation immediately increased and was maintained at 99–100%. The endotracheal tube was secured and tied in place. Anesthesia was continued at 1.5–2% isoflurane and was maintained without incident throughout the ensuing surgical corrections. Plasma-Lyte^a was initiated at 75 mL/hr. The patient was assessed to be stable. After patient stabilization, it was determined that primary resection of the GE mucosa and surgical correction of the other BOAS components were deemed necessary to resolve this patient's acute onset of respiratory distress.

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Approximately 45 min transpired between patient stabilization and the beginning of corrective surgery. Routine surgical IV fluid maintenance was started at 218 mL/hr (10 mL/kg/hr) and 480 mg of cefazolin (22 mg/kg) was administered IV at the beginning of corrective surgery. A temporary tracheostomy tube was placed between the second and third tracheal rings to aid in safe patient recovery prior to surgical correction of the anatomic defects.

The first surgical correction performed was a routine staphylectomy. Resection of the caudal margin was performed with Metzenbaum scissors, using the base of the tonsilar crypts as the limit of resection. The soft palate mucosa was closed in a simple continuous pattern using 3-0 polyglactin 910. Primary resection of the GE was the second surgical procedure that was performed. The redundant and edematous GE mucosa was resected at the base of the median and lateral GE mucosal folds with Metzenbaum scissors. The GE mucosa was closed in a simple continuous pattern with 4-0 polyglactin 910 individually on either side. Each separate, continuous pattern originated at the ventral middle of the GE mucosal fold and extended laterally to the base of the tonsilar crypt (Figure 3). Two separate suture patterns were used to help preserve the midline of the GE mucosa while trying to avoid any lateral deviation of the epiglottis (Figure 4).

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Following resection of the GE mucosa, routine surgical correction of the stenotic nares was completed with a number 11 scalpel blade via a vertical wedge resection technique and closed with 3-0 poliglecaprone 25 in an interrupted pattern.⁷ The last surgical correction involved the removal of the everted laryngeal saccules, which were sharply dissected and amputated at their respective bases after the patient had been extubated.¹

The patient recovered without any complications. The temporary tracheostomy tube was removed approximately 36 hr after placement. Histopathology of the GE mucosa noted mild, chronic, suppurative, and lymphoplasmacytic laryngitis with marked edema and fibroplasia. The patient was discharged with cephalexin 500 mg (23 mg/kg) PO BID, diphenhydramine 50 mg (2.3 mg/kg) PO BID, and with a tapering dose of prednisone that was initiated at 20 mg PO q 24 hr. Cephalexin was prescribed for prevention of any oral contamination and infection that may occur at the surgical sites. Diphenhydramine was prescribed for its sedative and antihistaminic effects and prednisone both for its anti-inflammatory and antifibrotic properties during the healing process.^13,14 The owners were instructed to hand-feed meatballs to the dog from an elevated position.

Follow-up laryngeal examination was performed 9 days postoperatively (Figure 5). The GE mucosa was observed to be healed. The epiglottic range of motion was assessed as normal.

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Discussion

In review of the literature, the authors noted a paucity of information regarding the extent of involvement of GE mucosa, its surgical correction, and technique in BOAS. Bedford described transient and dynamic displacement of the GE mucosa on inspiration into the aditus laryngitus and then returning to its normal subepiglottic anatomic position upon expiration in dogs with BOAS.¹⁵

The authors describe a case of static displacement of edematous GE mucosa, leading to sustained obstruction of the larynx and rima glottidis with accompanying epiglottic entrapment. Transient displacement of the GE mucosa back into its normal subepiglottic anatomic position was not observed during expiration in this patient, which has been described by Bedford. Traditional surgical management of the GE mucosa has involved resection of mucosa with scissors and then allowed to heal by second intention in patients with dynamic displacement of the GE mucosa.¹⁵

An intraoperative decision for the surgical margins of the GE mucosa was made subjectively. The redundant GE mucosa was resected to the level of the GE fold. Resection at this level was made with the goal to create both a confluent mucosal surface with a minimal amount of tension and redundant mucosa upon closure. Alternatively, the use of a CO₂ laser for tissue cutting and coagulation on mucosal surfaces could be used to perform this surgical procedure.¹⁶

A potential complication with primary closure of the GE mucosa includes concern against excessive tension between the epiglottis and the GE mucosa. This tension could lead to increased luminal exposure of the glottis with a resulting increased risk for aspiration pneumonia. In the long term, stricture formation at the surgical wound site could lead to a tethering effect on the epiglottis and conceivably cause a similar effect.

Fluoroscopic assessment of epiglottic function prior to or subsequent to definitive surgery would have been ideal in this case. A fluoroscopic study was not performed in this case because of the emergent nature, acute decompensation, and concerns regarding anesthetic duration. At the time of writing, the patient has shown no signs of increased or chronic coughing and has not been diagnosed with aspiration pneumonia (10 mo postoperative).

Conclusion

This case report is a unique presentation of BOAS that exemplifies how increased negative pressure within the airway can lead to edema and displacement of the GE mucosa, causing complete obstruction of the larynx, epiglottis, and rima glottidis. To the authors' knowledge, there is no literature describing complete obstruction of the larynx and rima glottidis by edematous GE mucosa in dogs secondary to BOAS. Additionally, the authors describe a novel technique for primary closure of the GE mucosa in two separate, simple continuous suture patterns. In this patient, the obstruction of the rima glottidis was the most significant component contributing to acute dyspnea. Surgical resection and primary closure of the GE mucosa resolved this patient's dyspnea, and no further complications were observed.

Objectively, the authors were unable to quantify how much of an effect the other confounding variables (elongated soft palate, stenotic nares, and everted laryngeal saccules) and their surgical correction contributed to the improvement of this patient. However, in the authors' opinion, the obstruction caused by the displaced GE mucosa was the overwhelming component of dyspnea in this patient. This conclusion is supported by the picture of laryngeal obstruction by the GE mucosa (Figure 1) and the immediate return to 100–99% oxygen saturation after intubation. Alternatively, a more conservative approach, standard surgical correction of BOAS defects and placement of a temporary tracheostomy tube, may have resolved this patient's dyspnea.

Static displacement of edematous GE mucosa may become an additional secondary component of BOAS in some dogs. In this patient, primary resection and closure of the GE mucosa resulted in a good outcome and may be a consideration in other similar cases. More information on the reported outcome and potential complications of primary closure of GE mucosa will be required to determine if this technique can be recommended in the future in dogs with this secondary component of BOAS.