A 10-month-old, female spayed Labrador retriever mix was referred to Metropolitan Veterinary Hospital Surgery Service due to a history of exercise intolerance and wheezing that was first recorded after being taken in by a local humane society. Radiographs from the referring veterinarian showed significant dilation of the cranial esophagus containing what appeared to be food as well as evidence of aspiration pneumonia (Figure 1). A contrast esophagram was performed by the same veterinarian subsequently and this examination was suggestive of a vascular ring anomaly. Despite these findings, the dog did not have a history of any episodes of vomiting or regurgitation during the 4 weeks of observation at the humane society. The dog was receiving amoxicillin-clavulanic acid 250 mg PO q12h (Clavamox; Zoetis, Kalamazoo, MI, USA) and ciprofloxacin 125 mg PO q12h (Cipro; Bayer Inc., Mississauga, Ontario, Canada) when initially evaluated at Metropolitan Veterinary Hospital.
Initial physical examination revealed no signs of dyspnea; however lower respiratory stridor, suggestive of stricture, was auscultated during panting. The dog was bright and alert, normothermic, and had no evidence of other congenital anomalies. The remainder of the physical examination was unremarkable. Likely differential diagnoses for the cranial esophageal dilation included vascular ring anomaly, or less likely esophageal stricture, foreign body, or neoplasia at the level of the heart base.
Because of the atypical history mostly related to respiratory signs and the older age of the patient, advanced imaging was recommended for surgical planning prior to the procedure. Computed tomography (CT) evaluation (Picker PQS Third Generation CT Scanner; Coral Springs, FL, USA) of the thorax identified a segmental megaesophagus extending throughout the cervical and cranial thoracic region with termination of dilation at the level of the heart base (Figure 2). At this level, the aortic arch had a bifid course with a large left-sided normal branch and a smaller right-sided segment (approximately one half the size as the left arch) coursing from the level of the cranial aspect of the aortic arch and anastomosing with the proximal aspect of the descending aorta. The smaller right-sided branch encircled the trachea causing severe mediolateral luminal narrowing of the trachea at the level of the cranial most aspect of the aortic arch and was also encircling the esophagus at the level of the heart base. The esophagus was also compressed and bounded dorsolaterally on the left by the normal left-sided aortic arch, laterally on the right by the trachea and ventrally by the main pulmonary artery. The esophagus caudal to the vascular anomaly was minimally distended. The left subclavian artery arose from the normal left aortic arch and there was a lack of a normal brachiocephalic trunk. The right subclavian artery arose from the aberrant right aortic arch and there was a very short bi-carotid trunk that arose from the confluence of the aortic arch cranially. The pulmonary parenchyma was normal with no evidence of aspiration pneumonia or increased attenuation to indicate fibrosis from a previous aspiration. The remaining intrathoracic structures and the captured intra-abdominal structures were normal.
Diagnosis consisted of a double aortic arch (smaller right-sided aberrant branch and normal left-sided aortic arch) encircling both the esophagus and trachea resulting in compression of both of these structures at the level of the heart base with subsequent development of a segmental megaesophagus. Concurrent vascular anomalies resulting in atypical origins of the right subclavian and carotid arteries were also present.
Four weeks after performing the CT scan, the patient was admitted to the hospital for surgical correction of her double aortic arch. She was placed under general anesthesia for surgery with a standard protocol. She was premedicated with hydromorphone (Akorn, Inc., Lake Forest, IL, USA) 0.1 mg/kg body weight (BW), IM, and induced with diazepam (Hospira, Inc., Lake Forest, IL, USA) 0.25 mg/kg body weight (BW), IV, and propofol (PropoFlo28; Zoetis, Kalamazoo, MI, USA) 4 mg/kg body weight (BW), IV. General anesthesia was maintained with isoflurane (IsoSol; VEDCO, Inc., St. Joseph, MO, USA) and mechanical ventilation (Hallowell EMC Veterinary Anesthesia Ventilator Model 2002IEPro; Pittsfield, MA, USA) was provided throughout the procedure. Antibiotic therapy (Cefazolin; West-Ward Pharmaceutical Corp, Eatontown, NJ, USA), 22 mg/kg body weight (BW), IV, was administered every 90 min.
A routine right 4th intercostal lateral thoracotomy was performed. Upon completion of thoracic exploration, blunt dissection into the mediastinum was performed. Two nylon stay sutures (Ethilon; Ethicon, Inc., Somerville, NJ, USA) were placed for retraction of the mediastinum. No gross abnormalities were identified in the mediastinum other than the cranial megaesophagus and a 6 mm right aortic arch (Figure 3). Blunt dissection to isolate the aberrant vessel was performed. Temporary occlusion via vascular clamps for 10 minutes showed no change in heart rate or blood pressure. Ligation of the aortic arch was initially performed with 2-0 silk (Sofsilk; Covidien LLC., Mansfield, MA, USA) ligatures cranially and caudally. The vessel was then transected and each end was oversewn with 3-0 Prolene (Ethicon, Inc., Somerville, NJ, USA). Further dissection deep to the arch to the level of the esophagus was performed to ensure no obvious fibrous bands were causing further constriction (Figure 4). Orogastric intubation was performed and confirmed an appropriate diameter of the esophagus. Digital palpation of the trachea showed that constriction was significantly relieved. Routine thoracostomy tube placement was performed (Mila International, Inc., Florence, KY, USA). Routine thoracotomy closure and thoracostomy tube fixation was performed. Air was evacuated from the pleural cavity via the thoracostomy tube, restoring subatmospheric pressure.
The patient received an intercostal nerve block using bupivacaine liposome injectable solution (Nocita; Aratana Therapeutics, Inc., Leawood, KS, USA) intraoperatively and was maintained on continuous rate infusion (CRI) of fentanyl (Hospira, Inc., Lake Forest, IL, USA), initially. Upon transfer to the surgical theater, a technical error led to the patient receiving a substantially higher dose of fentanyl (64 mcg/kg bolus over 15 minutes) than planned (4 mcg/kg/hour). The infusion was discontinued for the remainder of the anesthesia. The patient developed sinus bradycardia following the administration of fentanyl and was treated with Atropine 0.02 mg/kg, IV (Med-Pharmex, Inc., Pomona, CA, USA) to which she responded adequately. Recovery from anesthesia was uneventful. Isoflurane was discontinued and the patient was extubated 10 minutes later. The patient was maintained on the same fluid supplementations until being transferred to the intensive care unit (ICU). The postoperative analgesic protocol also included a postoperative carprofen injection 4.4 mg/kg subcutaneously (Rimadyl; Zoetis, Kalamazoo, MI, USA) and fentanyl transdermal patch (Alvogen, Inc., Pine Brook, NJ, USA) 50 mcg/hour was placed on the dorsal cervical area.
On admission to the ICU, the patient was calm and comfortable and vitals were within normal range. Fentanyl administration at a dose of 4 mcg/kg/hour was reinstated 3 hours following extubation due to observed signs of discomfort on incisional palpation. From anesthetic recovery to discharge, the patient's clinical condition progressively improved. Parenteral medications were transitioned from CRI (Fentanyl 4 mug/kg BW per hour CRI) to transdermal (Fentanyl patch) and oral nonsteroidal anti-inflammatory medication (Rimadyl; Zoetis, Kalamazoo, MI, USA), 75 mg PO q12h. The patient's thoracostomy tube air and fluid production decreased progressively during hospitalization and the tube was removed 12 hours postoperatively. The dog's first meal was offered 16 hours postoperatively as meatballs of CM (Hill's Pet Nutrition, Inc., Topeka, KS, USA) fed with the patient's head raised. No complications occurred during each subsequent feeding until discharge.
The dog was discharged one day postoperatively with instruction for strict exercise restriction for 3 weeks, oral Carprofen (Rimadyl), and transdermal fentanyl patch. Her caregivers at Lake Humane Society were instructed to feed small frequent meals until reevaluation.
A recheck was performed at Metropolitan Veterinary Hospital 3.5 weeks postoperatively. Her foster reported that she had resolution of her clinical signs starting one day after surgery. She was acting like a normal puppy, with great energy with no evidence of wheezing. After discharge postoperatively she was being fed one cup of food 3 times daily for 2 weeks. She was reported to have 2 episodes of regurgitation while on this feeding regimen. This resolved after switching her to 1.5 cups of solid dry dog food twice daily. At the time of recheck, on physical exam she was eupneic and no wheezing was auscultated. Three-view thoracic radiographs were performed which showed widening of the trachea cranial to the heart base, resolution of previous ventral tracheal deviation, and static cranial esophageal dilation. She had continued to do well with twice daily feeding from a bowl on the floor. No elevated feeding had been required.