Sialolithiase chronique chez une jument Trakehner. Une jument Trakehner âgée de 11 ans a été présentée pour une masse mobile ferme au dessus du maxillaire gauche. La radiographie a révélé une masse ovoïde opaque et discrète. Une sialolithiase du canal parotidien gauche a été diagnostiquée. Le sialolithe a été excisé par voie transorale et s’est révélé contenir un foyer morbide organique. La jument s’est rétablie sans complications.

(Traduit par Docteur André Blouin)

No abnormalities were found during a general physical examination, with the exception of a mass (approximately 3 cm in diameter × 6 cm long) that was palpable under the skin overlying the left maxilla in the region of the 3rd cheek tooth. The mass was noted to be firm, freely moveable, and nonpainful on palpation. It did not appear to be adherent to underlying tissues or to the overlying skin. No other abnormalities were detected on oral examination of the mare. Differential diagnoses included sialolithiasis, sialodenitis, buccal neoplasia, a chronic tooth root abscess, metaplasia, or dystrophic calcification.

Radiographs of the skull revealed an ovoid mineralized opaque structure abaxial to the left maxilla, dorsocaudal to the commissure of the lips. The structure was well defined, discrete, and not attached to adjacent bony structures. A tentative diagnosis of left parotid duct sialolithiasis was made. Surgical excision by a transoral approach was planned for the next day. Blood was collected for routine presurgical serum biochemical tests and a complete blood (cell) count (CBC); all measured parameters were within normal limits.

The following morning, an IV catheter was placed in the mare’s left jugular vein. Penicillin G (Penicillin G Sodium, 10 million IU/vial; Novopharm, Toronto, Ontario), 22 000 IU/kg body weight (BW), IV, was administered 30 min preoperatively and continued perioperatively, q6h for 36 h. Phenylbutazone (Phenylbutazone injection, 200 mg/mL; Univet Pharmaceutical, Milton, Ontario), 2.2 mg/kg (BW), IV, q12h, was administered for 36 h. Preanesthetic drugs administered included acepromazine maleate (Atravet, 10 mg/mL; Wyeth Animal Health, Guelph, Ontario), 0.05 mg/kg (BW), IM; xylazine HCl (Anased, 100 mg/mL; Novopharm), 0.52 mg/kg (BW), IV; and butorphanol tartrate (Torbugesic, 100 mg/mL; Wyeth Animal Health), 17.5 μg/kg (BW), IV. Ketamine HCl (Vetalar, 100 mg/mL; Bioniche Animal Health, Belleville, Ontario), 2 mg/kg (BW), IV, and diazepam (Diazepam injection USP, 5 mg/mL; Sabex, Boucherville, Quebec), 0.05 mg/kg (BW), IV, were used to induce general anaesthesia. The mare was positioned in left lateral recumbency and maintained under general anaesthesia by using isoflurane (Isoflurane USP, 99.9%; Pharmaceutical Partners of Canada, Richmond Hill, Ontario) in 100% oxygen to effect.

A MacPherson dental speculum was placed backwards relative to the bits in the horse’s mouth to allow better visualization of the surgical field. The sialolith was palpated in the oral cavity beneath the left buccal mucosa, just caudal to the parotid papilla. A #10 scalpel blade was used to incise the tissue overlying the sialolith, using gentle, partial thickness strokes through the oral mucosa and subcutaneous tissues. Digital palpation revealed that the sialolith was contained in a fibrous capsule. The fibrous adhesions around the sialolith and the capsule were broken down digitally and the sialolith (~2 cm in diameter × 6 cm long; 50 g) was removed by hand.

To determine if the parotid salivary duct was patent, silastic tubing (3.5 gauge French urethral catheter) was placed through the incision and passed retrogradely up the parotid salivary duct. The tubing passed without resistance and saliva was noted dripping from the distal end of the tubing, thus confirming patency and function of the parotid salivary duct. The incision was left to heal by second intention. Dobutamine HCl (Dobutamine HCl Injection USP, 12.5 mg/mL; Sabex), 2 mg, IV, was administered over 15 min, prior to the uneventful recovery of the horse from general anaesthesia.

Postoperatively, the mare’s mouth was flushed every 4 to 6 h with a 0.1% betadine solution. The mouth was also flushed immediately after she had eaten water soaked, pelleted feed. The morning after surgery, food had become impacted in the pouch that formerly contained the sialolith. A dental speculum was placed and the food was removed manually. Following this, the mouth was again thoroughly flushed with a dilute betadine solution.

The mare was discharged from the AVC with instructions to the owner to continue flushing her mouth with a dilute betadine solution, using a 60-mL syringe, 2 to 3 times daily for a week. At this time, the horse was prescribed sulfamethoxazole/trimethoprim tablets (Novo-Trimel, 800 mg sulphamethoxazole, 160 mg trimethoprim per tablet; Novopharm), 20 mg/kg (BW), PO, q12h for 5 d. The mare recovered without incident and 8 mo later continued to eat normally. A small fibrous scar remained at the site of the sialolith extraction, but there was no evidence of new sialolith formation.

The chemical composition of the extracted sialolith was not analyzed. When the sialolith was sawed in half, a small piece of straw was discovered in its center, around which concentric layers of mineral appeared to have been laid down (Figure 1). The mineral composition of the sialolith was suspected to be calcium carbonate.

Figure 1 Photograph of the cut surface of the sialolith showing the piece of straw present within its center (~2 cm in diameter × 6 cm long).

Salivary calculi, or sialoliths, are an uncommon problem in the horse, reportedly occurring more frequently in donkeys (1–3). Unlike in other species, sialolithiasis in the horse most often occurs in the rostral portion of the parotid salivary duct (1,4–6). Sialoliths are usually single, as found in the current case, but occasionally multiple stones are present (2). They are generally smooth and oval in shape. In horses, sialoliths are most often composed of concentric layers of calcium carbonate surrounding a central nidus of organic matter (1,4,6).

The diagnosis of sialolithiasis is based on clinical signs and palpation. As in this mare, they are usually hard, painless enlargements, rostral to the facial crest at the level of the upper third cheek tooth (1,5). Radiographs may be used to confirm the diagnosis by demonstrating a discrete mineral opacity within the soft tissue in this region (5). Differential diagnoses include sialodenitis, tooth abscesses, and buccal tumors (1,5). Metaplasia or dystrophic calcification are other possible differential diagnoses.

The exact etiopathogenesis of sialolithiasis is unknown, but it is believed that organic matter acts as a nidus around which calcium salts are deposited (1,4,6). The organic matter may be a foreign body, such as grain or grass, entering the parotid duct through the salivary (parotid) papilla, or it may be cellular debris and bacteria as a result of sialodenitis (1,4). In the horse, sialoliths may grow to over 10 cm in length and parotid salivary duct obstruction may occur with large stones (1), which, in turn, may lead to retention of saliva, stasis, and proximal movement of bacteria, resulting in acute sialodenitis (4,5). Although not evident in this case, salivary gland dysfunction and oral mucosal ulceration caused by sialolithiasis may occasionally result in discomfort, dysphagia, and possible atrophy of the gland (1,4,5). In contrast to these reports, the owner of this case reported none of these complications.

Most documented cases of sialolithiasis have had an average chronicity of no more than a few months, with the longest previously reported case being 24 mo in duration (1–3,6). There appears to be no gender or age predisposition to sialolith formation (1). However, sialolithiasis is documented to occur more commonly in animals living in more arid environments (1,4).

Research in human medicine has shown that humans with a higher salivary calcium level may be predisposed to sialolith formation (1). It is theorized that this high salivary calcium level could be due to low myoinosito hexaphosphate (phytate) levels (1). Phytate is a crystallization inhibitor. Other factors that potentially could increase salivary calcium levels as a result of hypercalcemia include renal lesions, primary hyperparathyroidism (extremely rare in horses), granulomatous disease, and hypervitaminosis D (1). In this case, the horse demonstrated no clinical signs consistent with hypercalcemia, such as polyuria and polydypsia, or other lesions.

Surgical removal of sialoliths in humans is performed by a transoral approach and the incision is left to heal by second intention (1,5). Traditionally, sialolith extraction in horses was performed by a percutaneous approach (1,3), and this approach may still be used for stones that are too large for or not accessible by a transoral approach (5); however, it may cause complications, such as salivary fistula formation if duct closure fails (1,6). Inadvertent facial nerve damage is another risk with this approach, as the dorsal branch of the facial nerve traverses immediately dorsal to the surgical site (1). The transoral surgical approach to sialolith extraction is currently preferred in horses with sialolithiasis (1,6). Complications are few with incisions allowed to heal by second intention (1).

Secondary sialodenitis may be a complication of simple sialolith extraction and require postoperative lavage and antimicrobial therapy (5). The prognosis for this horse, as for most horses diagnosed with sialolithiasis, was good.

The author thanks Dr. Christopher Riley for his constructive criticism and contribution, as well as Kim Kulik for her help. CVJ