A 5-month-old sexually intact female Huacaya alpaca (cria 1) was referred to the Oregon State University Veterinary Teaching Hospital for evaluation of esophageal dysfunction. The cria had a history of intermittent respiratory noise since birth, lethargy, failure to thrive, ptyalism, and coughing since 3 months of age. Physical examination findings included thin body condition (body weight, 20.5 kg [45.1 lb]) and grossly visible peristaltic waves in the esophagus in the distal cervical region (between C3 and C6). Esophagoscopy revealed a narrowing of the intrathoracic portion of the esophagus. Examination of a lateral thoracic radiograph revealed gas distention in the cervical portion of the esophagus with fluid pooling in the caudal portion of the cervical esophagus cranial to the thoracic inlet and ventral displacement of the thoracic portion of the trachea. Examination of a barium esophagram revealed an abrupt truncation of the barium column 1.5 cm cranial to the carina that appeared to be caused by a focal extrinsic esophageal compression (eg, VRA). The esophagus was dilated with ingesta cranial to the truncation and appeared to surround the trachea hemicircumferentially within the thoracic inlet. Examination of a dorsoventral radiographic view revealed that the esophagus was displaced to the right, and the left descending aorta was visible. Thus, these findings reduced the likelihood that the truncation was caused by a PRAA.
At 5.5 months of age, cria 1 was anesthetized and positioned in right lateral recumbency. Thoracotomy was performed via the left third intercostal space. A left aortic arch with a persistent right ligamentum arteriosum and retroesophageal RSA were identified. Transection of the ligamentum arteriosum appeared to resolve the compression of the esophagus. However, access to the left aortic arch and RSA was limited and extensively impeded the ability of the surgeon to perform the procedure.
After surgery, a finely chopped and moistened diet was provided to the cria. Cria 1 developed persistent pleural effusion and continued to have intermittent episodes of regurgitation, gurgling respiration, and increased abdominal effort despite changes to the diet. Radiography of the thorax 10 days after surgery revealed pleural effusion, pulmonary atelectasis, and distention of the cranial portion of the esophagus with feed material. Examination of a barium esophagram revealed an esophageal dilation located cranial to the carina and attenuation of the barium column near the base of the heart. Thoracocentesis was used to remove approximately 1,100 μL of white fluid (total protein, 3.1 mg/dL; WBC count, 390 nucleated cells/μL [47% large mononuclear cells, 41% small lymphocytes, and 12% nondegenerate neutrophils]) that was consistent with a chylous effusion. Esophagoscopy was repeated and revealed a pronounced dilation of the lumen of the esophagus cranial to the narrowing of the intrathoracic portion of the esophagus.
Cria 1 was euthanatized 15 days after surgery. Necropsy revealed chylothorax and a focal intrinsic constriction (lumen diameter, < 1 cm) of the intrathoracic portion of the esophagus near the base of the heart that included dilation of the esophagus orad to the stricture and dilation aborad to the stricture. The left cranial lung lobes were adhered to the thoracic wall. Histologic examination of the esophagus revealed fibrosis and small-diameter myofibers (presumably caused by atrophy) of the smooth muscle at the site of constriction and less pronounced atrophy of the smooth muscle in the proximal and distal portions of the esophagus. Wallerian degeneration was observed in nerves located within the periesophageal connective tissue, the dorsal and ventral tracts of the lumbar portion of the spinal cord and spinal nerves, and the cauda equina.
A 7-month-old sexually intact male Huacaya alpaca cria (cria 2) was referred to the Oregon State University Veterinary Teaching Hospital for evaluation of weight loss, coughing, and regurgitation. The cria was reported to have increased respiratory effort after nursing during the neonatal period and was treated for weight loss and pneumonia at 2 months of age. A barium esophagram was performed at 6 months of age to determine the cause of intermittent episodes of regurgitation, coughing, and retching. Examination of the esophagram revealed an esophageal obstruction and megaesophagus. Thereafter, a pelleted ration was provided from an elevated feed bin, but clinical signs did not improve.
Physical examination findings included tachypnea (respiratory rate, 40 breaths/min), pyrexia (rectal temperature, 39.1°C [102.3°F]), and thin body condition (20.5 kg). Waves in the esophagus were visible along the distal cervical region (between C3 and C6). Radiography of the thorax revealed substantial distention of the esophagus and residual feed material within the esophagus extending from the upper to lower esophageal sphincter. Dorsal and right lateral extrinsic compression of the esophagus was observed at the level of the third intercostal space. Pulmonary infiltrates were observed in the caudal and ventral lung fields. Reevaluation of the previously obtained barium esophagram revealed focal compression of the dorsal wall of the esophagus with ablation of the barium column at the level of the third intercostal space (Figure 1). Saccular dilation of the esophagus with accumulation of barium cranial and caudal to the extrinsic compression of the esophagus was observed. Esophagoscopy revealed pooling of fluid and food material within the thoracic portion of the esophagus. Furthermore, a narrowing of the intrathoracic portion of the esophagus made it impossible to pass the endoscope beyond this point. Cria 2 was placed in right lateral recumbency, and fluoroscopy was performed, which revealed normal deglutition, nonprogressive esophageal peristalsis, and esophageal dilation and pooling of barium orad and aborad to the esophageal constriction at the third intercostal space.
Cria 2 was anesthetized and positioned in left lateral recumbency. Thoracotomy was performed via the right fourth intercostal space. A PRAA with a left ligamentum arteriosum was observed in the thoracic cavity. The cria was repositioned in right lateral recumbency, and thoracotomy was then performed via the left fourth intercostal space. The ligamentum arteriosum was ligated and transected. A catheter with an inflatable cuff was passed through the oral cavity into the esophagus and advanced to the level of the constriction. The cuff of the catheter was inflated (bougienage) in an attempt to increase the diameter of the lumen of the esophagus at the site of the constriction. Endoscopy performed during the surgery revealed a subjective increase in luminal diameter subsequent to bougienage at the stricture site.
Cria 2 recovered from anesthesia. It was provided small quantities of finely chopped feed. After consumption of the feed, the cria had grossly visible peristaltic waves in the esophagus and respiratory distress followed by regurgitation of the feed. Radiography performed 48 and 96 hours after surgery revealed consolidation of the ventral lung field, substantial dilation of the esophagus, and feed material within the esophagus extending from the thoracic inlet to the lower esophageal sphincter. Additionally, deviation of the dorsal esophageal wall with a banding effect was observed at the level of the third and fourth intercostal spaces, and there was narrowing of the trachea at the level of the third intercostal space. Cria 2 was euthanatized 4 days after surgery. Necropsy findings were consistent with PRAA, megaesophagus secondary to constriction caused by the PRAA, and aspiration pneumonia. The circumference of the distal portion of the esophagus was 18 cm, and the lumen of the esophagus was filled with feed. The circumference of the esophagus at the site of constriction where bougienage was performed during surgery was 7.5 cm. Histologic examination of tissues was not performed.
A 4-month-old sexually intact female Huacaya alpaca cria (cria 3) with a 3-week history of choking, which was first noticed at the time of weaning, and weight loss was evaluated at the Kansas State University Veterinary Medical Teaching Hospital. Physical examination findings included a thick white discharge from the oral and nasal passages and increased intensity of lung sounds during auscultation of the thorax. Cardiac murmur was not detected. Esophageal peristaltic waves along the neck were grossly visible, and regurgitated fluid and feed material were observed in the cria's pen.
Radiography of the neck and thorax revealed an ingesta-filled focal dilation of the esophagus cranial to the base of the heart and ventral deviation of the trachea caused by distention of the esophagus. Examination of a dorsoventral radiographic view of the thorax revealed a prominent left aortic arch that extended cranially to the middle of the second intercostal space as well as a second elliptical soft tissue structure located to the right of the trachea at the level of the fourth rib. Examination of a barium esophagram revealed distention of the cervical and cranial thoracic portions of the esophagus and a conical narrowing of a focal segment of the intrathoracic portion of the esophagus cranial to the base of the heart (Figure 2). Examination of a dorsoventral radiographic view of the thorax revealed a sigmoid deviation of the lumen of the esophagus with a right lateral deviation observed at the cranial aspect of the left aortic arch and a left lateral deviation 1 rib space caudal, which was at the location of an ellipseshaped soft tissue structure that was suspected to be a PRAA. The lumen of the esophagus tapered cranial to this second deviation (ie, left lateral deviation) at the level of the fifth intercostal space. These radiographic findings were considered evidence of the presence of a double aortic arch. Esophagoscopy revealed a stricture of the intrathoracic portion of the esophagus and pulsation of the surrounding vasculature along the esophagus. Echocardiographic examination findings were unremarkable, and arterial blood gas analysis results were within the reference ranges.
The cria was anesthetized and positioned in right lateral recumbency. Thoracotomy and resection of the fourth left rib were performed. The vasculature observed during radiography was not apparent via this approach. Therefore, the cria was repositioned in left lateral recumbency, and thoracotomy and resection of the fourth right rib were performed. Large vessels were identified and thought to be consistent with the vasculature observed during radiography. Structures surrounding these vessels were dissected to enable the surgeon to definitively define the vasculature. Unfortunately, the vasculature was inadvertently perforated, and the cria died because of exsanguination via hemorrhage through the perforation.
Necropsy findings included the identification of a left aortic arch and an aberrant RSA. The aberrant RSA originated from the aorta at a point 4 cm distal to the left subclavian artery, continued dorsally over the esophagus to the right, and caused compression of the esophagus, with moderate esophageal dilation cranial to the point of compression. Additionally, a patent RDA extended through a space between the pulmonary artery and the aberrant RSA. A ductus arteriosum originated from the pulmonary artery at a point 3 cm distal to the expected location of a left ductus arteriosum.
Postmortem examination was performed on 2 crias (crias 4 and 5) at the Oregon State University Veterinary Teaching Hospital. Cria 4 was a 6-month-old sexually intact female Suri alpaca with a history of intermittent regurgitation and loss of body condition beginning at 5 months of age. A barium esophagram was obtained by the referring veterinarian; evaluation of the esophagram revealed a focal ventral deviation of the trachea at the level of the third rib, barium accumulation at the level of the thoracic inlet, distention of the esophagus, and a focal region of narrowing of the lumen of the esophagus at the level of the third rib. These findings were consistent with an extrinsic dorsal compression of the esophagus. The caudal thoracic portion of the esophagus appeared normal. A tentative diagnosis of megaesophagus caused by a VRA was made by the referring veterinarian, and the cria was euthanatized. A left aortic arch was detected during necropsy. Additionally, an aberrant RSA was identified originating from the aorta at a point 3 cm distal to the origin of the left subclavian artery. An RDA extended through a space between the descending aorta and the right pulmonary artery at a point 1 cm distal from the origin of the RSA. The esophagus was dilated cranial to the ligamentum arteriosum.
Cria 5 was a 7-month-old sexually intact female llama that had intermittent episodes of choking and gurgling that began at 3 months of age. No abnormality was identified during physical examination by a referring veterinarian, and examination of a radiographic view of the pharynx and proximal portion of the esophagus revealed no abnormalities. The owner attempted to feed the cria a moist small particle feed, but the clinical signs persisted. At 5 months of age, evaluation of a barium esophagram revealed dilation of the cervical and thoracic portions of the esophagus cranial to the base of the heart and focal compression of the esophagus near the base of the heart. A tentative diagnosis of VRA was made. At 7 months of age, the cria had a thin body condition and a green liquid was observed around the mouth and nares, and the cria was euthanatized. Necropsy findings included a normal left aortic arch with an aberrant RSA originating at a point 3.5 cm distal to the left subclavian artery. An RDA originated at a point 1.3 cm distal to the origin of the RSA, extended through a space between the aorta and the right pulmonary artery, and caused compression of the esophagus. The circumference of the esophagus cranial and caudal to the ductus arteriosum was 11 and 5.5 cm, respectively.
To acquire an understanding of the frequency of VRAs and the relationship between VRA and megaesophagus in camelids, records were retrieved and reviewed for all camelids submitted to the Oregon State University Teaching Hospital or Veterinary Diagnostic Laboratory for necropsy from July 2002 to July 2009 (n = 366 camelids). In addition to the 5 crias reported here, 6 llamas and 4 alpacas with megaesophagus were detected during necropsy. Three of those 4 alpacas were ≤ 1 year old. One of these 3 young alpacas was a 2month-old cria with a VRA that consisted of a 1-cm-wide membranous band of tissue that originated from the right dorsal aspect of the aorta to the dorsomedial aspect of the right caudal lung lobe and crossed the esophagus caudal to the base of the heart. Most of the membranous band was formed by a thin-walled blood vessel that bifurcated near the aorta. It could not be definitively determined from the record if this vessel was the cause of the clinical signs of megaesophagus. However, the esophageal lumen was narrow enough that it would not allow the person performing the necropsy to pass a finger through the esophagus at the point where the membranous band crossed the esophagus. All 6 llamas and the 1 remaining alpaca were ≥ 5 years old, and VRA was not detected in any of these adult camelids.
Persistent right aortic arch
Right ductus arteriosus
Right subclavian artery
Vascular ring anomaly
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