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Parotid Duct Sialolithiasis in Horses

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Abstract

Parotid duct sialolithiasis was diagnosed in four adult mixed-breed mares. Successful surgical removal of the calculi was performed using a percutaneous approach. The salivary calculi were found to contain barley grains in the center, surrounded with mineral layers composed mainly of calcium carbonate and calcium oxalate.

Introduction

The salivary glands of horses secrete a large volume of saliva, which assists in softening roughage foods. Salivary flows have been reported to reach 50 mL/min in ponies during mastication of roughage foods.1 The major salivary glands of the horse are the paired parotid, mandibular, and sublingual glands. The parotid gland, which is the largest of the salivary glands in horses, extends ventrally from the base of the ear and wing of the atlas to the convergence of the maxillary and linguofacial veins, and to the caudal border of the mandible.1, 3 At the cranioventral angle of the gland, the parotid duct is formed from the convergence of several large ductules. The duct travels rostrally along the medial surface of the mandible and crosses underneath the mandible with the facial vessels. The duct follows the rostral border of the masseter muscle to empty at the parotid papilla, in the buccal vestibule, opposite the third upper premolar.2 The parotid duct terminates in the third upper cheek tooth and it is dilated before piercing the cheek.4

Parotid duct sialolithiasis is a condition observed in a salivary duct characterized by a calcific formation in the duct. A few reports on sialolithiasis in equine species have been recorded.5, 6, 7, 8, 9, 10 The current report documented four cases of parotid duct sialolithiasis in adult mares.

Section snippets

Horses

Four mixed-breed mares were referred to the Veterinary Teaching Hospital at Qassim University for treatment of hard swelling at the right cheek (Fig. 1). The ages of the mares were 6, 8, 9, and 9 years. History of the cases showed that the swelling developed progressively for more than 18 months. The mares had no history of difficulty in eating or drinking.

General physical examination for each mare showed a hard, freely moveable, and apparently painless mass located overlying the right maxilla

Results

Recovery from anesthesia was smooth, and no postoperative complications were observed. The calculi were elliptical, with mean diameter and weight of 7 × 3 cm and 100 g, respectively (Fig. 2). A longitudinal section of each calculus showed a barley grain embedded in its center forming a nidus around which a lamellar structure of a mineral deposition had formed (Fig. 3). Chemical analysis of the calculi showed that they consisted mainly of calcium carbonate and calcium oxalate.

Discussion

Parotid duct sialolithiasis is rarely encountered in domestic animals. It occurs more frequently in equine species than other species.5, 11 Within equine species, donkeys are the most susceptible to sialolith formation.5, 6, 9 For unknown reasons, equine sialolithiasis has been found only in the parotid duct.5, 11 Obstructive sialoadenitis with or without sialolithiasis of the submandibular gland are the most frequent salivary gland diseases in humans.12

Diagnosis of equine sialoliths can be

Acknowledgment

The authors thank Professor A. Alnadi (Department of Chemistry) for performing the chemical analysis of the salivary calculi.

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