CLINICAL COMMENTARYManagement of parotid gland trauma in horsesJ. F. HawkinsDepartment of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC.Correspondence: J.F. HawkinsEmail: jfhawkin@ncsu.eduKEYWORDSHorse, parotid gland, surgery, trauma, fluid accumulation, botulinum toxinThe parotid gland is the largest salivary gland in the horse and is located subcutaneously ventrally from the base of the ear and the wing of the atlas and extending dorsal and ventral to the jugular vein, maxillary vein and linguofacial vein. Rostrally the parotid gland is adjacent to the vertical ramus of the mandible. The parotid gland consists of multiple lobules of yellow to white, glandular tissue. The parotid gland secretes fluid into the oral cavity through the parotid salivary duct. The parotid salivary duct empties into the oral cavity at the level of teeth 308 and 309 or 408 and 409 (Dyce et al, 1987). Because of its subcutaneous location and limited fascial coverage the parotid gland is prone to external trauma. Lacerations in this area can involve the gland and manifest by saliva drainage from the wound. The drainage of saliva increases when the horse eats. In addition, lacerations involving the parotid duct from the angle of the mandible and adjacent to the facial artery and vein can result in fistula formation between the skin and the lacerated duct (Newton et al, 1997).One cause of parotid gland fistulation/drainage is iatrogenic surgical trauma. For example, during surgical removal of melanomas embedded in the parotid gland and during surgical approaches to the guttural pouch or mandible. A previously unreported complication of prosthetic laryngoplasty was detailed in the case report by Sanclemente et al (Sanclemente et al, 2025). Although anatomically close to the linguofacial vein it would be unusual to iatrogenically damage the parotid gland during prosthetic laryngoplasty (Rossignol and Ducharme, 2021). However, it should be straightforward to determine that lobes of the parotid gland were disrupted during the surgical approach to the larynx. The lobes of the parotid gland are characteristically dull white to yellow in appearance and are soft and friable (Dyce et al, 1987). Based on the author’s experience disruption of the parotid gland will lead to wound drainage or accumulation of fluid postoperatively (sialocele). When known surgical trauma to the parotid gland is recognized the author has left a portion of the incision open for drainage or placed a passive drain (Penrose) to encourage fluid drainage. Cases managed in this fashion have all been resolved without additional treatment.For the case reported here inadvertent disruption of the parotid gland during the laryngoplasty procedure resulted in severe, postoperative fluid accumulation. The sialocele formation contributed to a follow-up surgical procedure to explore the previous incision and to assess abduction of the arytenoid cartilage. Unfortunately, the laryngoplasty had failed necessitating a repeat laryngoplasty. Following repeat laryngoplasty the surgeons were faced with three treatment options including primary wound closure, leaving a portion of the incision open for drainage or placement of an active or passive drain. To minimize the risk for surgical site infection following repeat laryngoplasty the authors elected to perform a primary wound closure without establishing any form of drainage. Even without saliva leakage from the parotid gland the risk for a surgical site infection or seroma formation following a repeat laryngoplasty is high in the author’s experience. This case was complicated by an already high risk for postoperative seroma formation because of the repeat laryngoplasty and the iatrogenic damage to the parotid gland.A better option would have been open incisional drainage or placement of a Penrose drain. The primary reason being the high risk for ongoing drainage associated with the parotid gland and surgical trauma associated with repeat laryngoplasty. Another option would have been to place an indwelling suction drain. This decision is solely surgeon preference (Bischofberger, 2019). Both types of drainage solutions have their pros and cons and the advantages of preventing ongoing saliva accumulation outweigh the risk for a surgical site infection. Traumatic and iatrogenic parotid gland disruption can be managed successfully with open drainage and secondary wound healing and has been reported in humans and horses. In horses’ persistent drainage of saliva post parotid gland or duct injury has been managed with chemical involution of the parotid gland (Schmotzer et al, 1991).Sanclemente et al reported a novel method to decrease postoperative sialocele formation. Following repeat laryngoplasty, saliva drainage from the damaged parotid salivary gland was eliminated following intraglandular injection of botulinum toxin A. They reported that saliva accumulation ceased 5 days after the injection. The horse recovered successfully and was able to return to exercise without recurrence of exercise intolerance.The injection of botulinum toxin A and B in horses has been performed clinically and experimentally (Adam-Castrillo et al, 2004; DePuy et al., 2007; Gutierrez-Nibeyro et al., 2014; Jimenez et al., 2024). The reported dosages of botulinum toxin type A have ranged from 50 to 200 units and for type B have ranged from 50 to 2500 Units. In one study evaluating the injection of botulinum toxin type B into the external anal sphincter of horses no systemic effects were observed with dosages of 500, 1000, and 1500 units but a dosage of 2500 units resulted in lethargy, weakness and dysphagia for 14 days. This indicates an increased risk for clinical botulism following high dose administration of botulinum toxin B (Adam-Castrillo et al., 2004). To the authors’ knowledge no ideal dosage of botulinum toxin has been determined for the horse.In humans with parotid fistulas, drainage secondary to surgical procedures or trauma, the primary means of treatment has been establishment of drainage, second intention healing, bandaging, packing of the wound with gauze and intraglandular parotid injection of botulinum toxin (Chettyvattum et al., 2025; Hao et al., 2023; Jeong et al., 2024; Marks et al., 2024; O’Keefe et al., 2022; Santos et al., 2025; Send et al., 2018; Tighe et al., 2015). Type A botulinum toxin is the preferred agent to stop secretion of saliva from the parotid gland. The primary mechanism of action for botulinum toxin is the blocking of acetylcholine release and other neurotransmitters. The blockage of acetylcholine release decreases or eliminates saliva secretion and production from the parotid salivary gland. The botulinum toxin is injected percutaneously under ultrasonographic guidance (Marks et al., 2024). Dosages of botulinum toxin used in humans range from 5 to 100 units. Currently, in humans intraglandular injection of botulinum toxin A is the preferred method of resolving saliva fistulation secondary to an injured parotid gland.The authors of this case report used an empirical dose of 100 units of botulinum toxin A to manage persistent drainage from the surgically damaged lobe of the parotid gland. The author is not familiar with any experimental evidence of the effect of botulinum toxin A on secretion of saliva from the equine parotid gland. However, there has been an additional report of two horses with parotid trauma successfully managed with the intraglandular injection of 200 units of botulinum toxin A (Jimenez et al., 2024). Therefore, based on these three cases dosages of 100 to 200 units of botulinum toxin A could be used to manage persistent parotid salivary gland drainage of saliva (Jimenez et al., 2024; Sanclemente et al., 2025) without complications.Fortunately, parotid gland disruption secondary to a surgical approach to the equine larynx for laryngoplasty is rare. If lobes of the parotid gland are identified during a surgical approach to the larynx damage to the gland could be minimized by using blunt dissection to separate the gland from the linguofacial vein. In addition, the use of the LigasureTM device has been recommended to cauterize damaged portions of the parotid gland and minimize the risk for postoperative secretion of saliva in humans (Prokopakis et al., 2005). In general, the implantation of drains associated with equine laryngoplasty has been discouraged because of the presumptive risk of increased incidence of a surgical site infection. However, if this complication is encountered in additional cases leaving a portion of the incision open to allow drainage rather than completely close the surgical incision should be considered. The author has managed laryngoplasty seroma formation with targeted incisional suture removal to allow passive drainage of seroma from the surgical site and has not experienced an increased risk for a surgical site infection (Rossignol and Ducharme, 2021).In conclusion, damage to the parotid salivary gland can lead to fistulation, chronic drainage of saliva or sialocele formation and these complications can be managed with a variety of options. Based on the collective experience in humans, the intraglandular injection of botulinum toxin A should be considered to resolve this unusual complication in horses.