Bilateral choanal atresia in a cat

Abstract

A 7-month-old female spayed domestic shorthair cat was presented for investigation of stertor, open mouth breathing without apparent distress, and chronic bilateral nasal discharge that was unresponsive to antibiotics. Complete bilateral bony choanal atresia was diagnosed with computed tomography and nasopharyngoscopy. Choanal atresia is an uncommon congenital condition where the choana (nasal passage into the nasopharynx) is blocked by abnormal bone or soft tissue uni- or bilaterally. The cat’s clinical signs improved dramatically immediately after trans-palatal surgical correction. Post-surgical complications included the development of nasopharyngeal scar tissue and subsequent stenosis, persistent right-sided nasal discharge, and permanent damage to the right eye (blindness and cataract formation). Nasopharyngeal stenosis was managed with repeated balloon dilatations and temporary stenting, and the owner reported an excellent quality of life at 8-month follow-up. Bilateral bony choanal atresia has not been previously reported in cats. Uni- or bilateral choanal atresia should be considered in young cats presenting with refractory stertor, chronic nasal discharge, and/or open mouth breathing.

Case Report

A female intact domestic shorthair kitten was evaluated at 4 weeks of age for bilateral mucopurulent nasal discharge, stertor, open mouth breathing, wheezing, mild ataxia, and small stature compared with littermates. The kitten was part of an orphan litter and prior history was unknown. Ataxia was suspected to be secondary to viral-induced cerebellar hypoplasia given similar signs in the littermates. Whole body radiographs were unremarkable. The cat failed to respond to six separate courses of amoxicillin trihydrate/clavulanate potassium (Clavamox; Pfizer) over 6 months.

The cat was referred for further evaluation at 7 months of age. The cat was of small stature for age, weighing 2 kg with a body condition score of 5/9. Bilateral mucopurulent nasal discharge was present with no airflow detected through either nostril. Stertor and open mouth breathing without apparent distress were noted. Referred upper airway sounds were heard on thoracic auscultation. The cat was mildly ataxic in the rear limbs.

Differentials for the respiratory condition included a congenital anatomical defect — such as nasopharyngeal stenosis or choanal atresia — nasopharyngeal polyp, viral upper respiratory infection, or foreign body. Results of a complete blood count, serum chemistry profile, urinalysis, prothrombin time, activated partial thromboplastin time and pre- and 2-hour postprandial bile acids were within reference intervals, and the cat was negative for feline immunodeficiency virus and feline leukemia virus based on enzyme-linked immunosorbent assay. These tests were performed to rule out a hepatic shunt, given the cat’s small stature, and to evaluate the cat’s candidacy for anesthesia.

The cat was anesthetized to perform computed tomography (GE CT/e single-slice helical scanner; GE Healthcare). Transverse helical images of the nasal cavity were initially obtained pre- and post-contrast using 3 mm slice thickness and 2 mm intervals. Subsequent post-contrast images were obtained using 1 mm slice thickness and intervals. Communication between the nasal passages and the nasopharynx was prevented by a complete osseous bridge covered by a mucous membrane connecting the hard palate (palatine bone) to the presphenoid bone. The nasal turbinates were poorly defined throughout both sides of the nasal cavity, especially ventrally and on the left, consistent with suspected nasal turbinate lysis. There was focal rightward displacement of the ventral portion of the nasal septum at the level of the upper premolars. There was decreased density of the right medial orbital wall, suggesting lysis, although partial volume averaging of this curved surface and mild patient rotation could artifactually contribute to the CT appearance. Fluid attenuating material in the nasal passages and frontal sinuses was consistent with nasal secretions. CT results indicated complete, bilateral bony choanal atresia apparently caused by congenital fusion of the hard palate to an extension of the presphenoid bone (Figure 1).

Figure 1

All images are displayed in a bone window: (A) parasagittal reconstructed CT image of the skull of the cat with choanal atresia, made immediately to the left of midline. The osseous bridge representing extension and fusion of the hard palate and the presphenoid bone at the level of the choana is indicated by the arrow. The nasal cavity (N) is filled with non-enhancing fluid density material, consistent with nasal secretions, and there is no communication between the nasal cavity and nasopharynx (NP), (S = sphenopalatine sinus). (B) Equivalent parasagittal CT reconstruction of the skull of a normal cat. Note the normal nasal turbinates and the air-filled choana (C) between the nasal cavity and nasopharynx. (C) Transverse CT image of the nasal cavity of the cat with choanal atresia, obtained at the level of the orbits. The patient’s right side is on the left side of the image. Note the decreased attenuation of the right medial orbital wall (arrows) compared to the contralateral side. This finding is most consistent with bone lysis, though the appearance may have been accentuated by partial volume averaging and mild patient rotation.

Following the CT scan, the nasopharynx was visualized using a flexible pediatric bronchoscope (Olympus BF 3C160 bronchoscope, 5.3 mm outer diameter). On retroflexed view, the choanae were occluded by firm tissue covered by a mucous membrane continuous with the nasopharynx. No opening from the nasopharynx into the nasal passages was identified. A 5-French (Fr) catheter was inserted antegrade through the left and right nostrils but could not be passed beyond the medial canthi. The nares were flushed with saline whilst visualizing the nasopharynx, but no saline appeared in the nasopharynx, confirming the diagnosis of complete, bilateral choanal atresia.

A midline trans-palatal approach to the left nasopharynx and caudal nasal cavity was made. The bony septum at the choanae was removed with a Hall air drill until a 5-Fr catheter could be passed from the nares into the oropharynx. Abundant nasal secretions were removed by suction. A similar approach was attempted on the right side, but the turbinates and nasal septum were displaced to the right. Mass-like tissue was removed from the dorsal right nasal cavity and no normal nasal turbinates were noted. The bone of the right ventral orbit appeared to be partially absent and this space was entered inadvertently. An opening between the right nasal cavity and nasopharynx was then made as described above. Histopathology of the mass-like tissue consisted of normal skeletal muscle, salivary gland and adipose tissue, pieces of fibrovascular connective tissue, and multiple small fragments of bone. Perivascular lymphocytic infiltrates were seen in the specimens. Respiratory epithelium and nasal turbinates were not noted in the biopsy specimens, suggesting that the mass was a hamartoma (histologically normal tissues located at an aberrant site) with associated inflammation, as evidenced by the lymphocytic infiltrates. No organisms were seen; cultures were not performed. The hamartoma was thought to represent the underlying cause for presumed lysis of the right ventral orbit. 5-0 Monocryl was used to close the soft palate in a double layer and the hard palate mucosa in a single interrupted layer. The cat was given one preoperative dose of cefazolin intravenously (Ancef; Sandoz, 22.5 mg/kg) and one postoperative dose of meloxicam subcutaneously (Metacam; Boehringer Ingelheim Vetmedica, 0.1 mg/kg).

Postoperatively, the throat and nares were suctioned as required. The cat was managed with buprenorphine (Buprenex; Reckitt, 0.01 mg/kg) intravenously every 6 h, ampicillin sodium/sulbactam sodium (Unasyn; Pfizer, 22 mg/kg) intravenously q8h, and ocular lubrication (q4h OD). The right eye appeared normal postoperatively but became exophthalmic within 12 h, with an incomplete pupillary light response and poor vision, as indicated by a weak menace response. Swelling was attributed to postoperative hemorrhage and edema. The cat was discharged 2 days postoperatively with buprenorphine (0.01 mg/kg) orally q8h, amoxicillin trihydrate/clavulanate potassium (Clavamox; Pfizer, 14 mg/kg) orally q12h, and a petroleum eye lubricant to the right eye q4h. The owner reported that the cat was breathing more comfortably on day 5 postoperatively compared with initial presentation and was rarely open mouth breathing. Moderate right-sided mucoid nasal discharge was noted.

Six days postoperatively, the cat was diagnosed with worsening right-sided exophthalmia; blindness as evidenced by negative menace and dazzle responses; a large, centrally-located corneal ulcer; and anterior uveitis. The exophthalmia was thought to be secondary to the inadvertent exploration of the right orbital space during the surgery and subsequent development of retrobulbar cellulitis. This likely lead to uveitis, exposure keratitis, and the development of a corneal ulcer. Blindness was thought to be a combination of optic nerve damage due to surgery and exophthalmia, and severe inflammation leading to uveitis. A temporary tarsorrhaphy was performed on the right eye and ciprofloxacin 0.3% (Ciloxan; Hi Tech), hyaluronan 0.3% (I-Drop; I-Med Pharma), and flurbiprofen 0.03% (Ocufen; Bausch and Lomb) drops started. In addition to the previously prescribed antibiotics and pain medication, the cat was also prescribed marbofloxacin (Zenequin; Pfizer, 5 mg/kg) orally once daily for 10 days and piroxicam (Feldene; Teva, 0.3 mg/kg) orally once daily for 5 days. Exophthalmia had resolved by day 21 when the tarsorrhaphy was relieved; however, the cat remained blind in the right eye. The cat was spayed at this time. The corneal ulcer had resolved at the time of tarsorrhaphy removal, the uveitis had improved and was resolved by day 55, and the eye eventually developed a mature cataract and keratoconjunctivitis sicca. The eye was treated with cyclosporine 2% ophthalmic solution long term. The eye otherwise remained quiescent without any apparent discomfort to the cat.

Nasopharyngeal balloon dilatation was performed on postoperative days 21, 42, 55, and 63, based on increasing stertor and nasal discharge observed by the owner and the presumptive postoperative development of nasopharyngeal stenosis. Temporary nasopharyngeal stents were placed on days 63 and 73 in an attempt to reduce stenosis. Dilatation on days 21 and 42 was performed as follows: A 5-Fr red rubber catheter inserted antegrade through the left nasal cavity passed into the nasopharynx, but when inserted into the right side the catheter was seen entering the nasopharynx through the same left-sided opening, suggesting that only one opening remained patent. A 6-Fr esophageal balloon dilatation catheter (Boston Scientific) was passed antegrade into the right nostril until the proximal aspect of the balloon was visualized with the retroflexed pediatric bronchoscope. The balloon was placed at the level of the one patent choana and dilated to a pressure of 3 ATM for one minute. Upon balloon deflation, a more patent choana was seen. On days 55 and 63, dilatation was performed with a 7 mm hepato-biliary balloon stent dilated to a pressure of 10 ATM (Cordis Palmaz Corinthian IQ), with the coil stent device removed prior to insertion. This device was used because the nasopharynx had become more stenotic and the esophageal balloon could not be passed. Prednisolone (Orapred; Teva) at 1 mg/kg per day orally was started on day 42 and prednisolone acetate 1% ophthalmic drops (Omnipred; Pacific Pharma) were instilled into both nares twice a day starting on day 63 to attempt to reduce scar tissue formation.

After the balloon dilatation on day 63, an indwelling temporary nasopharyngeal stent was placed using a standard 8-Fr red rubber catheter (Tyco; Mansfield, MA). The catheter was passed antegrade into the nasopharynx approximately 0.5 cm past the level of the surgically created choanal opening with assistance of a retroflexed endoscope. For better flexibility in securing the stent in place, the catheter was replaced with an 8-Fr nasoesophageal tube (Tyco, Kendall) placed, in the same manner as previously described, to the level of the nasopharynx. The stent was secured with skin sutures and remained in place for 9 days until unintentional removal (Figure 2A). On day 73, the stent was replaced with a 10-Fr polypropylene catheter (Tyco, Kendall) and remained in place for 7 days before intentional removal. The stent was placed in a similar manner and secured via skin sutures (Figure 2B). Polypropylene was chosen instead of rubber given that it is more rigid in nature and would potentially be more successful at maintaining a patent choanal opening.

Figure 2

(A) The cat with the original temporary rubber stent (8 Fr) placed to the level of the nasopharynx; (B) the cat with the second temporary stent (10 Fr) made of more rigid polypropylene and placed to the level of the nasopharynx

After stent placement, the cat was reported to do very well. At re-check examination on postoperative day 123, the owner reported a persistent mild right-sided nasal discharge, but there was airflow through both nostrils. At follow-up examinations on days 169 and 232, the cat continued to do well and rhinitis signs remained static. Prednisolone was reduced to 1 mg/kg per os every other day on day 232.

Bilateral choanal atresia has only been previously described in human infants, occurring in between 1 in 5000 to 1 in 9000 live births. ¹ Females are affected twice as often as males, and most cases involve bony obstruction. Children with either uni- or bilateral choanal atresia are predisposed to other congenital anomalies; the incidence is as high as 75% in cases of bilateral disease. ¹ Concurrent abnormalities include colobomas, mental or growth retardation, and genitourinary, cardiac, and aural abnormalities.

One case of unilateral choanal atresia in a cat has been described and was successfully treated with transnasal surgical repair and placement of a stent. ² Unilateral atresia has also been reported in dogs, ³ humans,^4–7 camelids, ⁸ horses, ⁹ sheep, ¹⁰ and baboons. ¹¹ Clinical signs were nasal discharge (uni- or bilateral), stertor, open mouth breathing, and small stature.^2–4 Choanal atresia should be considered in a young animal with chronic upper respiratory signs or as a cause of neonatal death, particularly if signs of upper airway obstruction are noted.

Choanal atresia and nasopharyngeal stenosis are diagnosed via a combination of advanced imaging and endoscopy. Choanal atresia is a congenital anomaly in which there is a bony or membranous occlusion preventing communication between the nasal cavity and pharynx, whereas nasopharyngeal stenosis is a narrowing (congenital or acquired) of this passageway.

Surgical approaches to correct choanal atresia include transnasal, transpalatal, and trans-septal, with methods of correction including resection and/or puncture with subsequent dilatation. In human medicine, transnasal puncture with Fearon dilators is described in membranous stenosis, but must usually be combined with stenting. ⁶ The transpalatal approach allows the best visualization of the defect; however, it has been reported to lead to palatal abnormalities as children grow. ¹ Endoscopy-assisted trans-septal opening of the passage can avoid the anatomic abnormalities that can follow the transpalatal approach; however, a need for later removal of granulation tissue around the choanae is common.^5,12–14

Surgical correction of nasopharyngeal stenosis in cats has been described with some success. In one report, an intraluminal stent was placed to maintain patency, but complications included granulation tissue around the stent requiring surgical resection and continued upper respiratory congestion. ¹⁵ Another report describes resection of the stenotic region via a midline transpalatal approach and repair of the defect using a nasopharyngeal advancement flap with resolution in the clinical signs for more than 2 years after surgery. ¹⁶ Other reports describe successful management of nasopharyngeal stenosis with repeated balloon dilatations as with the cat in the current report. The most common complications were mild conchal necrosis and persistent nasal discharge.^17,18

In the cat of the current report, the choanal atresia was completely bony; therefore, a transnasal approach was not feasible and equipment was not available to attempt trans-septal endoscopic resection. The transpalatal approach used was successful in creating a single patent choanal opening; however, development of nasopharyngeal stenosis due to scar tissue and unilateral blindness were significant complications. Blindness developed because of exophthalmos, optic nerve damage, and uveitis — presumably secondary to retrobulbar inflammation caused by inadvertent surgical exploration of this space. The presence of a hamartoma (possibly causing osseous resorption because of the mass effect) and suspected chronic rhinitis, which may have caused bone lysis, were likely the predisposing factors for the lack of bone in the ventromedial orbital wall. Balloon dilatation and stenting were used to manage the nasopharyngeal stenosis resulting in a good reported quality of life at 8-month follow-up.