Nasal stenosis arising from developing premolar dentition in a horse.

This research discusses a case of a young thoroughbred racehorse suffering from respiratory obstruction, believed to be due to the development of its premolar dentition leading to nasal stenosis, a condition not previously reported in literature. This finding was made using CT imaging postmortem, after the horse was euthanized due to economic reasons.

Background

• The development of premolar dentition in horses can deform the support bones which can lead to replica cysts.
• The permanent premolar cheek teeth erupt and grow in length from two to four years of age, occupying a large portion of the mandible and maxilla during the early life of horses.
• Supernumerary dentition, and non-dental sinonasal cysts have been reported as causes of upper respiratory obstruction, affecting the nasal septum and the ventral conchal sinus.
• Previous reports did not address the obstruction of the nasal passages by the normal dentition development process.

Case Description

• A two-year-old thoroughbred colt in race training was presented with a suspected exercise intolerance and respiratory obstruction. The horse was found to have a loud pan-respiratory stridor during exercise since he began cantering.
• An attempt at upper airway endoscopy revealed bilateral nasal stenosis, a condition where the nasal passages are narrowed. The passage of a 9 mm diameter flexible fibrescope was impossible due to this obstruction.
• Use of a smaller (5 mm) fibrescope allowed for visualization of the nasal passages. Notable were axial deviations of the lateral wall of the ventral nasal meatus on each side. Visually, the mucosa at the affected sites appeared normal with no overt inflammation or nasal discharge. There was also noted moderate resting left-sided laryngeal dysfunction.

Investigation and Findings

• The severity of the horse’s condition resulted in it being euthanized on economic grounds. Postmortem CT images of the horse’s head were then obtained using a four-slice helical CT scanner.
• Helical images collimated to a slice thickness of 1 mm were retrospectively reconstructed using a 0.7 mm slice thickness in bone and soft tissue windows. The images were then exported into a DICOM workstation and manipulated using OsiriX version 3.3.2 32 bit.
• The imaging helped determine that developing premolar dentition was the cause of the bilateral stenosis of the nasal passages.