Surgical Debulking and TransEndoscopic Noncontact Diode Laser Application for Treating a Sinonasal Myxoma in a Horse.

Equine sinonasal myxomas (SNM) are very rare; only a few cases/small case series are reported in veterinary literature. The purpose of this report is to describe the diagnostic and surgical procedure adopted to approach the neoplastic mass in a case of equine SNM. A 5 year old, Murgese gelding was presented with mild serous nasal discharge, minimal facial swelling, decreased airflow from the right nostril, and dull frontal sinus percussion. Diagnostic imaging, including endoscopy, revealed a pale mass in the caudal portion of the right middle meatus, which developed inside the right conchofrontal sinus and nasal cavity and deviated the nasal septum to the left side. A large frontonasal bone flap was created with the horse in general anesthesia, aiming to remove the lesion and perform further diagnostic investigation. The mass had the shape of a small orange, the caudodorsal and rostral part having a hard wall, whereas the ventral part being friable; the inside was hollow, containing a viscous and transparent liquid. Surgical excision was broad but incomplete, and therefore after surgery, a standing transendoscopic diode laser irradiation and photoablation of small residual lesions per nasum were performed. Microscopically, the mass consisted of spindle-shaped cells, loosely arranged within an abundant, light blue myxoid matrix. On the basis of clinical and pathologic findings, the diagnosis of sinonasal myxoma was made. Although benign and slowly growing, myxomas usually tend to infiltrate the surrounding tissues; as a consequence, recurrence is very likely after surgical excision. In the case described herein, the combination of a surgical excision, transendoscopic diode laser irradiation, and photoablation provided a positive outcome, until at least 14 months after surgery.