The most common cause of acquired oronasal fistulas is periodontal disease. The roots of the maxillary teeth are located close to the nasal passage. When vertical bone loss occurs due to periodontal disease, inflammation and infection can dissolve the thin shelf of bone and epithelium that separates the mouth from the nose. Oronasal fistulas can be subtle in their clinical signs, and practitioners often ask for tips on the best methods to repair these defects with a single surgical attempt. This month’s column, the first of two devoted to oronasal fistulas, discusses clinical signs and diagnosis of oronasal fistulas. The case of a small Fry Fry, a recent patient, is a 2-kilogram Chihuahua that presented with vague signs of possible oral discomfort, sneezing, gagging, coughing, and difficulty breathing. When Fry’s owner showed me a video of one of these episodes, I knew this was more than just a reverse sneeze. The video showed a severe gagging episode with difficulty breathing, more than what might be seen with a reverse sneeze. On conscious examination, a slight heart murmur was ausculted. No cough was elicited on tracheal palpation. Oral examination revealed significant calculus covering nearly all the teeth and gingival recession of certain teeth. The clinical signs of oronasal fistulas may be subtle and limited to scant unilateral or bilateral serous nasal discharge or increased sneezing and gagging, which the owner may notice when the patient eats or drinks. Identifying an oronasal fistula that exists at the periphery of an existing tooth is a job for the periodontal probe in anesthetized patients. If the probe extends 10 or more millimeters into the gingival sulcus, you can safely say there’s an oronasal fistula occurring there. Although the diagnosis needs to be made in the anesthetized patient, you can get a hint of whether a patient has an oronasal fistula by inquiring about increased sneezing at home and by assessing the palatal surface of the maxillary canine teeth. If an oronasal fistula is present on the palatal surface of the maxillary canine teeth, large amounts of calculus may be found accumulating in this area (Figure 1). Figure 1: Be suspicious of a preexisting oronasal fistula if you see this much calculus accumulation on the palatal surface of the maxillary canine teeth. Although the most common site for an oronasal fistula is around the maxillary canine teeth, watch for fistulas around the maxillary premolar teeth. In fact, Fry’s conscious examination showed no suggestion of oronasal fistulas on the palatal surface of the maxillary canine teeth, and probing these teeth showed no excessive pocketing. In Fry’s case, a probing depth of 10+ was found between the left maxillary second and third premolar teeth (Figure 2). Raising a mucoperiosteal flap in this area revealed severe bone loss and oronasal communication. Figure 2: A periodontal probe reveals an oronasal communication at the palatal surface of the left maxillary second and third premolar teeth in a 14-year-old Chihuahua that was presented for gagging, coughing, sneezing and difficulty breathing. A common misconception is that a tooth must be missing for an oronasal communication to be present. On the contrary: Every dachshund that has a 10+ probing depth on the palatal surface of its maxillary canine teeth has an oronasal fistula brewing. As practitioners, we frequently encounter mobile teeth that are easy to extract, especially in small breed dogs. Even when a tooth is loose enough to remove without a flap, the extraction site ideally should be closed with a tension-free mucoperiosteal flap with releasing incisions. This is due to the fact that there’s a good chance that a preexisting oronasal fistula is present if there were deep periodontal pockets around the loose tooth. If the site is not closed with a tension-free flap, a chronic oronasal fistula will result (Figure 3). Figure 3: An oronasal defect develops after a mobile right maxillary canine tooth extraction site was not closed with a tension-free mucoperiosteal flap. I see a good number of dachshunds and Yorkshire terriers that have had a maxillary canine tooth extracted at their primary care veterinarian’s practice a few months earlier, only to find a sizable oronasal defect develop in the area of the extracted canine tooth. After the extraction, new presenting complaints of increased sneezing may be encountered, particularly when drinking water. These oronasal fistulas existed prior to the procedure, but they resulted in more clinical signs once there was no longer a tooth present to plug the oronasal communication. This scenario can be avoided if the site of the maxillary canine tooth is closed with a tension-free flap. The flap is carefully sutured to a nonepithelialized recipient bed. Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar Vets in Robbinsville, N.J.
