Removal of sialoliths using the intraoral approach in 15 horses

Abstract

This study describes the use of an intraoral approach for sialolith removal in horses. All horses resumed their previous activity after surgery. Sialoliths were composed mainly of calcium carbonate, containing a nidus of plant material. The removal of sialoliths via an intraoral approach results in a high success rate with minimal complications.

Sialoliths are solid calculi that develop within the parotid duct, or less commonly, within the salivary gland (1–6). Sialolithiasis is more common in arid environments and has a high incidence in donkeys (1). Affected equids present with a non-painful, movable, firm structure that is palpable on the lateral aspect of the face [(1–3), Figure 1]. Clinical signs when present may include fever, dysphagia, quidding, halitosis, anorexia, weight loss, and signs of focal pain around the sialolith (1,2,5,6). Diagnosis of equine sialoliths can be made by physical examination alone, although radiography can aid in certain cases (1,3,6,7). Possible differential diagnosis includes sialoadenitis, tooth abscess, or buccal tumors (3,8). The etiology of sialolith formation is unknown; however, it is believed that the inciting cause is presence of organic matter in the duct (1–3,6). Definitive treatment of sialolithiasis is surgical removal, which can be performed by either an intraoral or a transcutaneous approach (1–6). When using the intraoral approach, sialolith removal can be achieved by enlarging the parotid duct opening (6) or by incising the oral mucosa over the sialolith (1). In this study, we report the removal of sialoliths by the latter technique, using the intraoral approach, in 15 horses. We describe the surgical technique, results of surgery, and chemical analysis of the removed calculi.

Figure 1.

A sialolith that is a non-painful, movable, firm structure palpable on the lateral aspect of the face.

Between March 2010 and February 2014, ambulatory equine clinicians from Israel were asked to inform the authors of any horses with sialoliths treated with intraoral removal and provide appropriate documentation and the sialolith itself. A documentation table was provided, and filled out by each practitioner. Diagnosis of sialolithiasis was based on clinical presentation and palpation. Data collected in the documentation tables included breed, age, gender, clinical signs, time between sialolith appearance and surgery, side affected, surgical approach and technique, post-operative management, and complications. Patient follow-up was achieved by telephone conversation with the owner.

All sialoliths were removed by an intraoral approach under sedation in standing position (11 horses) or under general anesthesia (4 horses). The most common sedatives used were xylazine hydrochloride (Thiazine 100; Ceva Animal Health Pty, Glenorie NSW, Australia), 0.5 mg/kg body weight (BW), IV, or detomidine hydrochloride (Domosedan; Orion Pharma AS Animal Health, Oslo, Norway), 0.01 to 0.02 mg/kg BW, IV. After sedation, 5 to 10 mL of lidocaine hydrochloride (Esracain 2%; Rafa Laboratories, Jerusalem, Israel) was infiltrated percutaneously through the cheek along the sialolith using a 21-gauge 4-cm needle. A full mouth speculum was inserted and secured in an open position. The sialolith was palpated intraorally and an incision was made along its entire length, with a No. 10 scalpel blade. The sialolith was then separated from the mucosa by blunt dissection using Kelly hemostats, and manually removed. The separation of the sialolith from the duct required gentle and controlled force, since the sialolith was typically firmly attached to the mucosa. After removal of the sialolith the incision was left open to heal by second intention. Post-operative treatment included intraoral lavage with tap water with or without salt dissolved in the water. Phenylbutazone (Phenylbutazone; Vetmarket Marketing, Shoam, Israel), 2.2 mg/kg BW, PO, q12h, and Penicillin G Procaine (Norocillin; Norbrook, Lenexa, Kansas, USA), 22 000 U/kg BW, IM, q12h, were used according to the clinician’s preference. Fisher’s exact test was conducted to compare sialolith occurrence between sides (right versus left) and gender (male versus female).

Sialolith samples were submitted to the G. V. Ling Urinary Stone Analysis Laboratory, University of California-Davis, USA, for crystallographic analysis.

Fifteen horses were diagnosed with sialolithiasis, among them 10 mares, 3 geldings, and 2 stallions. Mixed breed horses were the most commonly affected breed (7/15; 46.7%). Quarter horses accounted for 3 of the 15 cases (3/15; 20%). Other affected breeds included Arabian (2/15; 13.3%), Paint (1/15; 6.7%), Appaloosa (1/15; 6.7%), and a Tennessee walking horse (1/15; 6.7%). The horses ranged in age from 2 to 22 y with a mean of 10.2 y and a median of 8 y.

All sialoliths were located in the parotid duct and none of the horses had sialoliths within the parotid gland parenchyma. The calculi were recognized by the characteristic firm, mobile, and mostly painless longitudinal enlargement located laterally, slightly ventral and rostral to the facial crest. Most horses did not show any clinical signs (9/15; 60%). Some horses showed clinical signs including, anorexia and weight loss (4/15; 26.7%), pain upon palpation (1/15; 6.7%), and dysphagia (1/15; 6.7%). Time between sialolith appearance and surgery was noted in 7 horses and varied from few months to several years. Although most sialoliths appeared in mares (9/15; 60%) and on the right side (9/15; 60%), no significant difference was found between either gender (P = 0.14) or side (P = 0.28). One horse had bilateral sialolithiasis (1/15; 6.7%). Fourteen sialoliths were available for examination and analysis. The length of the sialoliths ranged from 2.5 cm to 10 cm with a median of 4.75 cm. Most of the calculi (13/14; 93%) presented as single sialoliths but several of them (6/13; 46%) presented as 2 or more fragments that fit each other very well with smooth fitting margins (Figure 2). One horse had 2 separate calculi.

Figure 2.

Photographs of sialoliths. A — A sialolith made up of more than one fragment. B — A sialolith with a nidus of plant material lodged in the hollow center of the stone.

Two sialoliths were removed during hospitalization at the Israeli Veterinary Teaching Hospital (VTH) due to unrelated causes (uterine torsion and splint fracture removal). The remaining cases (13/15; 87%) were presented to 7 private equine clinics located around the country, specifically for sialolith removal. The surgery was performed by ambulatory practitioners except for the 2 cases operated at the VTH by specialists. Four horses underwent general anesthesia (GA) (4/15; 26.7%), although 1 was under GA for another procedure (splint bone fracture removal). The remaining horses (11/15; 73.3%) had surgery under standing sedation and local anesthesia. All sialoliths were removed by an intraoral approach and the incision was left to heal by second intention. In 1 horse the incision was partially sutured using 2-0 polydioxanone monofilament (PDS) placed in a simple interrupted manner. Eleven horses received Phenylbutazone and 6 horses received Penicillin G Procaine for several days.

Post-operative complications included swelling of the surgical site in 2 horses observed on the lateral aspect of the face (2/15; 13.3%) and difficulty to stand after GA in 1 horse (1/4; 25%). The horse recovered and was stable and able to ambulate the same day and both swellings resolved after a few days without intervention. All horses resumed their previous level of work after the surgery.

Fourteen sialoliths were available for analysis. The chemical analysis of the sialoliths revealed that all stones were composed mainly of calcium carbonate (60% to 95%) and the rest was apatite. In most cases, the sialolith had a nidus of plant material (12/14; 85.7%), which was lodged at the hollow center of the stone (Figure 2).

In the current study, an intraoral approach for sialolith removal was applied in all horses resulting in minimal complications and excellent prognosis. To our knowledge, this is the first case series of sialoliths removed solely by the intraoral technique. In recent years several authors have recommended the intraoral approach over the transcutaneous one, due to frequent complications encountered when using the transcutaneous approach (3,5–6). The main complication, associated with the transcutaneous approach, is oro-cutaneous fistulation which was reported in up to 35% of the cases (1). Additional complications included surgical site infection, facial nerve damage, and incisional edema (1,5). According to previous reports (1,6), the intraoral approach results in a low complication rate and this is supported by the current study. The single surgery related complication in the present study was swelling of the surgical site produced from accumulation of saliva, hematoma, or seroma. Seroma or hematoma is not specific to the intraoral approach and can develop in any surgical site or traumatized area and is usually absorbed spontaneously (9). Accumulation of saliva may have occurred because of the traumatized oral mucosa, damaged parotid duct, and inappropriate drainage; however, this resolved quickly and without interference, so further investigation was not pursued. Difficulty to stand after surgery was another complication seen in 1 horse during the study but this also resolved without intervention. Complications related to recovery from GA are not uncommon, and may increase the morbidity and mortality of the horse as described in previous studies (10–11). Thus, performing procedures in a standing position under sedation is generally safer for the horse and often preferable. In the current study, 4 horses were operated under GA. In 1 case the horse was already under GA for removal of a splint bone fracture. In another case, the horse went through general anesthesia since it resisted the standing procedure, despite heavy sedation. The 2 remaining horses went through GA due to clinician’s preference. In 11 cases operated in a standing position under sedation and local anesthesia, horses tolerated the procedure without resistance.

In the current study, sialoliths were removed by cutting the mucosa over the length of the sialolith, as opposed to the technique described by Haralambus et al (6), in which the parotid duct papilla was surgically enlarged. We believe that detecting the parotid duct papilla during surgery is unnecessary. The current study demonstrates that incising directly over the stone may minimize surgery time and decrease morbidity.

Clinical signs due to the presence of sialolithiasis are not uncommon as shown in the present study and previous reports (1,6). Owing to the simplicity of the surgery, the good results and the possibility for developing clinical signs, prophylactic removal of the stone after initial diagnosis is advocated.

It seems that the incidence of sialolithiasis is higher in arid environments, suggesting feeding regimes influence occurrence (1–2). Due to low precipitation in arid regions, as in our geographic environment, horses are mainly fed straw and barley and rarely green feed. It seems reasonable to assume that diet composed of dry hay, and possibly water deprivation, encourage sialolith formation. Furthermore, in 12 of 14 sialoliths that were analyzed, plant material was lodged in the center of the stone, emphasizing the importance of diet in the etiology of sialolithiasis.

The high concentration of calcium bicarbonate in the horse parotid saliva (12) is likely the reason that calcium carbonate is the main component found in equine sialoliths. Calcium carbonate was the main component of sialoliths in previous studies (1–2,6), and similar to the current report, some of those studies found a mild addition of apatite minerals as well (1,6). To our knowledge, this is the only case series reporting chemical analysis of sialoliths in horses. Some support for the influence of diet on sialolithiasis comes from the study of enterolithiasis in horses (13), which is highly correlated to an alfalfa rich diet and a lack of pasture feeding. Furthermore, enteroliths appear to grow outward from a central nidus, which can be rock fragments, mineral grains, feed material, and plastic or metallic objects (14). Although some similarities in the formation of the 2 calculi can be assumed, more studies concerning sialolith development and risk factors should be done to fully understand the etiology and pathogenesis.

In the current study, horses seem to develop sialoliths over a wide range of ages, even as young as 2 y, which is consistent with previous reports (1–2). As previously reported (2), in the present study, mares seemed to have a higher incidence of sialolithiasis but no statistical difference in gender predilection was established, perhaps owing to the small study group.

In conclusion, sialolithiasis is uncommon in horses, affecting mainly horses in arid environments. In the current study, we report successful removal of sialoliths via the intra-oral approach in 15 horses. The calculi were composed of calcium carbonate and apatite and had a plant material nidus in the center. The intra-oral approach can be readily performed in a standing horse, it does not require special equipment or hospitalization, and has a low complication rate. Based on the results of this study we recommend removal of sialoliths at the onset of diagnosis using an intra-oral approach.