Ultrasound-guided intraglandular injection of 10% formalin as a therapeutic alternative in a case of chronic fistula associated with parotid duct stenosis

This case report describes the clinical evolution of a traumatic injury to the parotid salivary duct treated with two ultrasound-guided intraglandular injections of 10% formalin, as an alternative to retrograde chemical ablation.
A chronic fistula of the left parotid salivary duct was diagnosed in a 2-year-old Lusitano stallion. Initial treatment by retrograde chemical ablation with 10% formalin failed. Re-evaluation one year later revealed, through fistulography, severe ductal injury with disruption of its anatomy, which precluded retrograde injection. Ultrasound-guided intraparotid injection was therefore chosen as an alternative treatment. 6 and 9 ml of 10% formalin were injected in two sessions five days apart, under sedation and with anti-inflammatory treatment. No local inflammation or adverse effects were observed. Ultrasonography demonstrated increased echogenicity of the treated parotid gland compared to the contralateral gland as secretion decreased in frequency and volume. Two years later, the fistula had resolved completely without complications.
Ultrasound-guided intraglandular injection of 10% formalin represents a viable alternative when retrograde injection is not feasible. Further studies are required to evaluate long-term safety and efficacy.