A 6.3-kg (13.9-lb) 4-hour-old female Huacaya alpaca cria, accompanied by its dam, was admitted to a veterinary medical teaching hospital because of respiratory distress and difficulty nursing since birth (day 0). On admission, the cria was bright, alert, and responsive; it was able to stand on its own, and had a suckle reflex. The cria was tachycardic (heart rate, 160 beats/min) and had open-mouth breathing (80 breaths/min); its rectal temperature was within the reference range at 37.5°C (99.5°F). The oral mucous membranes were cyanotic, and no airflow could be detected from either nostril during expiration. Introduction of a 5F flexible red rubber tube into the ventral meatus of each nostril revealed the lack of patency of either of the choanae. On the basis of these findings, a presumptive diagnosis of congenital complete bilateral choanal atresia was made. Evaluation of the head by CT was recommended to confirm the diagnosis and determine the type of choanal obstruction.
Supplemental oxygen delivery was initiated via face mask at a rate of 5 L/min. The patient was anesthetized and intubated orotracheally, and CT images of the nasal cavities and nasopharynx were acquired with 1.25-mm-thick slices in the transverse plane and reconstructed with imaging software.a Evaluation of the images revealed membranous obstruction of the nasal cavities bilaterally (3 mm thick on the left side and 5 mm thick on the right side) at the level of the choanae (Figure 1). These findings were consistent with a diagnosis of congenital complete bilateral membranous choanal atresia. The owner was informed that the prognosis was poor and that the condition could have a genetic component,1,2 but declined euthanasia and elected surgery. The cria was immediately taken to surgery.
Computed tomographic images (reconstructed sagittal [A] and transverse [B] views) of the nasal cavities of a neonatal alpaca cria that was evaluated because of respiratory distress. The images were acquired with 1.25-mm-thick slices in the transverse plane. The CT evaluation revealed a membranous obstruction of the nasal cavities bilaterally (3 mm thick on the left side and 5 mm thick on the right side) at the level of the choanae consistent with choanal atresia. The membranous obstructions are indicated in the sagittal (white arrow) and transverse (black arrows) views. Scale = 1 cm.
Citation: Journal of the American Veterinary Medical Association 250, 9; 10.2460/javma.250.9.1036
A 5.2-mm fiberoptic bronchoscopeb was introduced into the oral cavity and retroflexed into the nasopharynx to allow visualization of the caudal aspect of the choanal membranes. The site to be perforated was located by placement of gentle pressure on the choanal membrane with a 10F red rubber tube passed through the right nostril. The stylet of a 14-gauge IV catheter was introduced through the red rubber tube and was used to perforate the choanal membrane at the intended site (Figure 2). A guidewire was introduced through the stylet, the stylet was removed, and a tissue dilatorc was passed in an over-the-wire manner to dilate the puncture in the choanal membrane. The tissue dilator was replaced with an 8-mm-diameter balloon dilatord (size selected on the basis of measurements on the CT images), which was insufflated to the maximum pressure (830 kPa [8.2 atm]) for a duration of 10 minutes. The balloon dilator and guidewire were then removed. The procedure was repeated on the left side. Patency of each choana was verified by instillation of saline (0.9% NaCl) solution through each nostril under endoscopic guidance. A temporary tube tracheostomy was performed in the proximal cervical region at the end of the procedure.
Still images obtained from a video recording of retrograde rhinoscopy during surgical correction of the persistent choanal membranes of the alpaca in Figure 1. Surgical correction of the right choanal membrane is shown. A—The fusiform-shaped, persistent choanal membranes are indicated (arrows). The soft palate is located on the bottom half of the image. Correct insertion of the catheter was confirmed by tapping a red rubber tube against the choanal membrane. B—The stylet of a 14-gauge IV catheter was advanced through the red rubber tube to perforate through the choanal membrane. C—A guidewire (0.025 inches × 180 cm) was inserted through the stylet across the persistent choanal membrane. D—The stylet was replaced with a tissue dilator to enlarge the opening in the choanal membrane. E—The tissue dilator was replaced with an 8-mm-diameter balloon dilator that was insufflated to its maximum pressure for 10 minutes. F—The resulting enlarged perforation can be seen with the guidewire still in place. The procedure was repeated for the contralateral choana.
Citation: Journal of the American Veterinary Medical Association 250, 9; 10.2460/javma.250.9.1036
During anesthesia, lactated Ringer solution with supplemental glucose at a final concentration of 2.5% was administered (5 mL/kg/h [2.3 mL/lb/h]). Assessment of the patient's PCV and serum total solids concentration 3.5 hours after anesthetic induction revealed anemia (PCV, 22%; reference range, 25% to 37%) and hypoproteinemia (total solids concentration, 35 g/L; reference range, 45 to 55 g/L). Whole fresh blood from the dam (total volume, 46 mL) was administered IV because of active surgical bleeding and potential hemodilution. The cria's arterial blood pressure decreased substantially (from 73 to 50 mm Hg, as measured by direct blood pressure) during surgery, and colloid administration was needed. On the basis of the serum total solids concentration and the assumption that passive transfer was deficient because of the patient's inability to nurse, fresh frozen plasma administration was initiated during anesthesia (5 mL/kg/h [2.3 mL/lb/h] for a total of 37 mL) and continued after surgery to deliver a total volume of 160 mL (25.4 mL/kg [11.5 mL/lb]). The total crystalloid volume administered during anesthesia was 15 mL (2.4 mL/kg [1.1 mL/lb]). The tracheostomy tube was left in place for the postoperative period.
Perioperatively, the cria received ceftiofur sodium (2.2 mg/kg [1.0 mg/lb], IV, q 12 h) and 1 dose of flunixin meglumine (1.0 mg/kg [0.45 mg/lb], IV). Five hours after anesthetic recovery, the cria was found with signs of respiratory distress due to obstruction of the tracheostomy tube. Arterial blood gas measurements revealed severe hypoxemia (Pao2, 25 mm Hg; reference range, 80 to 100 mm Hg) and severe hypercapnia (Paco2, 64 mm Hg; reference range, 35 to 45 mm Hg) with a pH of 7.23. The tracheostomy tube was replaced, and signs of respiratory distress resolved. Thereafter, the tube was changed every 8 to 10 hours from days 0 to 3, and a mucolytic agent (acetylcysteine, 20 mg [0.1 mL of a 200-mg/mL solution]) was instilled every 4 hours into the tracheostomy tube. The cria was able to stand and nurse without assistance ≤ 8 hours after surgery.
On day 1, thoracic auscultation revealed increased lung sounds with intermittent wheezes. Thoracic radiographic examination revealed a bronchointerstitial pattern in the caudodorsal lung lobes. Results of a CBC revealed relative neutrophilia (9.77 × 109 cells/L [89%]; reference range, 34.9% to 63%) with a band neutrophil count of 0.11 × 109 band cells/L (reference range, 0 × 109 band cells/L to 0.36 × 109 band cells/L), 1+ toxic changes in neutrophils (evidenced by the presence of 1 or more Döhle bodies/cell, mild basophilic cytoplasm, or both; scale, 1+ [mild] to 3+ [severe]) indicating the presence of inflammation, and lymphopenia (0.55 × 109 cells/L [5%]; reference range, 18.3% to 41.9%).3 Aspiration pneumonia was suspected, and treatment with ceftiofur sodium was continued at the previously described dosage until the cria was discharged from the hospital.
On day 3, the tracheostomy site was temporarily occluded to allow patency of the choanae to be assessed. The cria became severely dyspneic with no airflow evident from either nostril, consistent with bilateral obstruction of the choanae. The owner declined euthanasia, and revision of the previous puncture sites was performed. With the cria under general anesthesia in sternal recumbency, the 5.2-mm flexible fiberoptic bronchoscope was introduced through the left nostril. The previous surgery site was observed, and a guidewire was passed through the initial puncture site into the nasopharynx. A 4-mm-internal-diameter silicone endotracheal tubee was threaded over the wire, pushed through the puncture site in the choanal membrane, and left in place to serve as a stent. The procedure was repeated on the right side. At the end of the procedure, each stent was cut close to the nostril opening and sutured in place. The tracheostomy tube was again left in place for the postoperative period.
The cria recovered uneventfully from anesthesia and was able to nurse without apparent disturbance from the stents. After removal of the tracheostomy tube on day 4, the cria failed to breathe through its nostrils and resumed open-mouth breathing. Endoscopic evaluation with a 2.85-mm-diameter flexible endoscopef revealed the presence of a small flap of granulation tissue obstructing the tracheal lumen immediately distal to the tracheostomy site, with the nasal stents remaining patent. Excessive granulation tissue in the trachea was removed with grasping forceps, which resolved the dyspnea. The tracheostomy site was allowed to heal by second intention.
On day 5, the nasal stents became occluded with mucus, and the cria resumed open-mouth breathing. Nebulizationg was performed, with a solution of acetylcysteine (20 mg [0.1 mL] diluted into 5 mL of distilled water) administered through a face mask to facilitate aspiration of mucus with a medical suction device. Thereafter, nebulization and cleaning of nasal stents by aspiration were necessary to maintain patency of the stents and were performed every 2 to 6 hours until stent removal. During hospitalization, the cria remained alert, nursed well, and gained 2 kg (4.4 lb) in 13 days.
On day 14, both nasal stents were removed, and the cria did not develop further signs of upper airway obstruction. No major complications occurred, except occasional accumulation of mucoid secretions in the nostrils, which resolved with serial intranasal instillation of 0.5 mL of physiologic saline solution.
The cria was discharged from the hospital on day 17; the owner was given instructions to continue nasal administration of physiologic saline solution as needed and to continue treatment with ceftiofur (2.2 mg/kg, SC, q 12 h) for 8 more days. Considering the potential genetic component of choanal atresia,1,2 it was suggested that the owner exclude this alpaca from the breeding population. At 5 months of age, follow-up by telephone with the owner revealed the cria was healthy, gaining weight normally, and breathing with a mild respiratory noise only. According to the owner, its subsequent growth was slower than that of herdmates of similar age during the first year of life; however, at 24 months of age, its weight was considered appropriate for an adult alpaca, and its body condition score was considered appropriate. At the time of last follow-up, the patient was 3 years old; the owner reported that the respiratory noise had gradually decreased over the first 2 years and was subsequently difficult to detect. The alpaca was kept in the herd for fiber production and had not been bred.
Discussion
Choanal atresia is a congenital membranous or bony obstruction of the caudal aspect of the choanae that obstructs the communication between the nasal cavities and the pharynx. As reported in a survey of experienced camelid veterinarians (n = 34) in the United States, choanal atresia is the most common congenital maxillofacial defect in camelids; it was reported to occur in 0.75% of all births of llamas and in 0.48% of all births of alpacas (the total number of births was not presented).4 Unilateral or bilateral choanal atresia has also been described in other domestic animals such as dogs,5 cats,6 sheep,7 and horses8 and has been reported to occur in 1 of 8,000 live births of people.9 Choanal atresia has been associated with a low survival rate in New World camelids.10 Because these species are primarily nasal breathers, affected juvenile animals are unable to breathe while suckling, which typically results in fatal aspiration pneumonia.
Various theories have been proposed to explain the embryological origin of choanal atresia, including failure of buccopharyngeal membrane breakdown, persistence of the nasobuccal membrane, or persistence and misdirection of mesoderm in the nasal cavities during embryogenesis.11 In human medicine, other congenital anomalies are common in patients with choanal atresia.12 Likewise, choanal atresia in llamas has been associated with neurologic, cardiac, gastrointestinal, or skeletal anomalies in 10 of 30 (33%) cases.13 However, the cria of this report did not have other maxillofacial abnormalities or other congenital defects detected. The etiopathogenesis of choanal atresia in camelids is not well understood, and an autosomal recessive mode of inheritance has been suggested.14 Until further information is available, owners should be prompted to exclude affected animals from the breeding population.
For the cria of this report, CT was elected as the primary imaging modality after a presumptive diagnosis of bilateral choanal atresia was made. In contrast to endoscopy or positive-contrast rhinography, CT allows determination of the type of obstruction (complete vs partial and membranous vs osseous), the length and location of the atresia plate, and the presence or absence of other craniomaxillofacial abnormalities.15 For these reasons, CT evaluation of the head has become the diagnostic tool of choice for evaluation of human patients affected by choanal atresia.16 The use of CT allowed the diagnosis of complete, bilateral, membranous choanal atresia in this 4-hour-old patient, thus permitting the use of an endoscope-guided balloon-dilation technique rather than passing a Steinman pin blindly.17
The surgical technique used for correction of bilateral choanal atresia in the cria of this report was novel and consisted of a transnasal balloon-dilation technique combined with retrograde rhinoscopy. Reports of successful treatment of choanal atresia in camelids are sparse,17,18 likely because of the poor outcomes after the procedure and the ethical issues related to treatment of a potentially heritable disease.10 Approaches that have been used for treatment of choanal atresia in domestic animal species include transnasal puncture with fluoroscopic guidance,17,18 nasal flaps,19 and transnasal laser ablation techniques.20,21 In people, transpalatal and transnasal approaches are described,22 with the transnasal endoscopic approach being the most widely accepted repair technique because of its lesser invasiveness and lower complication rates. A transnasal approach was initially attempted and subsequently abandoned in the cria described here because visualization of the choanal plate was suboptimal. With the bronchoscope placed transorally and retroflexed in the nasopharynx, the caudal aspect of both choanal membranes could be observed. Perforation and dilation of each choanal membrane required endoscopic visualization and included a balloon-dilation technique similar to those described in recent human and small animal studies.23,24 Reported advantages of balloon-dilation techniques include the application of stable radial forces as opposed to shearing linear forces encountered during rigid dilation methods.23 Nevertheless, bilateral obstruction occurred 3 days after surgery in the present case, which necessitated a revision procedure. In humans, restenosis following transnasal endoscopic repair is the most common postoperative complication, and it was reported to develop in up to 17 of 24 (71%) sides in patients that had the condition bilaterally in 1 study.25 During the revision procedure for the patient of the present report, nasal stenting was performed by placement of silicone endotracheal tubes secured to each nostril. Nasal stenting following surgery for choanal atresia remains a highly debatable topic in human medicine. Whereas some authors believe that nasal stenting is essential to stabilize the nasal airway and reduce the likelihood of restenosis,26 others report complications related to nasal stenting such as discomfort, localized ulceration and infection, and circumferential scar tissue formation after stent removal.27 Recently, no difference between groups was found regarding the incidence of restenosis in 20 human patients (10/group) following transnasal endoscopic choanal atresia repair with or without the use of stents.28 However, a higher complication rate (including granulation tissue formation, excoriation or erosion of the nares, premature extrusion, and stent dislodgement or blockage) was found for patients that had stents placed.24,28 In the cria of the present report, stent occlusion with mucus developed repeatedly after surgery and required intensive nursing care, including serial nebulization of a solution of acetylcysteine diluted in distilled water and aspiration of mucus with a medical suction device. The duration of nasal stenting following choanal atresia repair reported in the literature varies from 14 to 27 days in camelids17,18 and from 2 days to 4 weeks in people.29,30 Nasal stents were left in place in our patient for 12 days after the second procedure, and the outcome was successful. We speculate that nasal stents might have prevented the need for revision of the initial repair if they had been placed during the first surgical procedure.
Unlike horses and similar to human beings, camelids are primary but not obligate nasal breathers. Bilateral choanal atresia in primary nasal breathers results in respiratory distress and open-mouth breathing, but it is not immediately lethal as it would be in obligate nasal breathers. In a clinical report by Fulton et al17 in 1989, successful surgical treatment of bilateral choanal atresia in a llama by use of a transnasal breakthrough technique did not involve placement of a tracheostomy tube. In an earlier clinical report,18 a tracheostomy was performed first to allow tracheal intubation during surgical manipulations involving the head, and it assisted breathing during the immediate postoperative period. However, we were able to proceed with the endoscopically assisted transnasal balloon-dilation technique with the orotracheal tube in place. Postoperatively, the cria continued breathing through the tracheostomy tube, and the lack of airflow through the patent choanae might have contributed to the rapid onset of restenosis with fibrinous material following surgery. Patent nasal airflow was restored after the nasal stents were placed and the tracheostomy tube was removed. Another complication from the temporary tracheostomy included formation of exuberant granulation tissue during second-intention healing of the tracheostomy site. On the basis of our experience and others,17,18 we do not recommend performing a temporary tracheostomy routinely before transnasal balloon-dilation repair of choanal atresia and nasal stent placement owing to the complications that can arise from the tracheostomy. Therefore, careful postoperative monitoring is necessary to prevent obstruction of the nasal stents. Following stent removal, follow-up rhinoscopy is recommended to identify recurrent stenosis.
Acknowledgments
No source of funding was used for this clinical report.
Footnotes
Osirix imaging software, Pixmeo SARL, Bernex, Switzerland.
BF-160, Olympus Canada Inc, Richmond Hill, ON, Canada.
Multi-Lumen Central Venous Catheterization Set with Blue FlexTip Catheter, Catalog No. CS-14703, Arrow International, Reading, Penn.
Medi-Tech BMQ/8-4/5-8/75 [2502241], Boston Scientific-Meditech, Watertown, Mass.
COOK-SurgiVet, Dublin, Ohio.
11278 AUI/CE 0123, Karl Storz GmbH and Co KG, Tuttlingen, Germany.
MedPro Compressor Nebulizer System, AMG Medical Inc, Montreal, QC, Canada.
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