A 12-year-old Thoroughbred mare was evaluated for routine dental floating and vaccinations. During inspection of the mouth, a mass was noticed within the buccal soft tissues adjacent to the left maxillary arcade, situated at a rostrodorsal to caudoventral oblique angle at the level of the third and fourth premolar teeth. The mass measured 9 × 3.5 cm and was firm and freely mobile under the skin of the left cheek. The horse was sedated and a MacPherson mouth speculum was placed. Sharp enamel points were present along the buccal surface of the left maxillary arcade, and 2 buccal ulcerations were present at the level of the enamel points. The largest ulcer (diameter, 4 mm) was probed digitally, and a smooth firm surface was encountered. Lateral, oblique, and dorsoventral radiographs of the skull were obtained (Figure 1).
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
On both lateral and oblique views, a 7 × 3-cm well-demarcated mineral opacity structure is evident in the left buccal soft tissues (Figure 2). No involvement or connection to the maxilla or premolar teeth is apparent. The structure is ovoid with the caudal aspect slightly wider than the rostral aspect. A linear radiolucency is present centrally within the structure. On the basis of the radiographic findings, differential diagnoses include a mineralized foreign body or a sialolith.
Treatment and Outcome
Surgical exploration of the structure and associated soft tissues was performed through a transoral incision. An intraoral approach was used to avoid salivary fistula formation. The structure was a smooth white stone, measuring 6.5 × 2.5 cm, adhered to the buccal submucosa. The stone was removed, and a duct-type opening was palpable at the caudal aspect of the buccal pocket following removal. A contrast fistulograma was performed to assess the extent of the opening. A well-defined ductal structure was visible on the left lateral view (Figure 3), consistent in location with the parotid salivary duct.
After removal, the stone was radiographed. Concentric mineral layers were noted around a central 40 × 2.5-mm rectangular radiolucency. The stone was cut in half along the transverse axis, and a 2-mm thick foreign body was present centrally, consistent with straw. Chemical analysis of the stone was reported as calcium carbonate (95%) and calcium phosphate (5%).
A recheck examination 11 days after surgery revealed minimal external soft tissue swelling and minimal inflammation at the incision site, which had healed to approximately half its initial length. The buccal pocket was also decreased in size.
Sialolithiasis is uncommon in horses. In most published reports,1 clinical manifestation is similar to the case described in this report, with a nonpainful swelling along the cheek. In most cases, a piece of vegetative material is present within the stone, acting as a nidus for the sialolith formation. Barley and oat grains are most commonly reported.2,3 Access to the parotid duct is proposed to be through the buccal mucosal opening near the maxillary fourth premolar tooth or from a penetrating injury through the buccal mucosa into the duct.1,4
Radiography is an excellent tool for diagnosis of parotid duct sialoliths and to rule out other causes of buccal swelling, including sialoadenitis, tooth root abscess, neoplasia, and granulomas. Following transoral excision, the incision site is left to heal by second intention.4 Minimal complications have been reported with this technique, and the prognosis is good to excellent.1,4