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History

A 21-year-old, Mustang mare presented for approximately one month history of intermittent swelling caudal to the left mandible. This swelling was first detected two weeks after an episode of colic and was again noticed during a second episode of mild colic and pyrexia. At this time, the patient was treated with antibiotics and flunixine meglumine prior to referral. On physical examination, the patient was bright, alert, and responsive. Her temperature was mildly elevated (102 deg F), pulse rate was at the upper limit of normal (44 bpm), and respiratory rate was normal (16rpm). A large, warm, painful region of swelling extended from the caudal aspect of the mandibular ramus, dorsally to the ear base, and ventrally to the region of the throat latch. Initial radiographs demonstrated the reported soft tissue swelling but no other abnormalities. Subsequent CT imaging was performed.

 

CT Images

• The left parotid salivary gland is moderately enlarged (up to 5cm wide) and heterogeneous with rounded to lobular internal hypoattenuating and non-enhancing regions.

• At the rostral aspect of the gland, the parotid duct is tubular to saccular, containing similar non-enhancing material. The duct extends ventral to the mandibular body, where it contains a small (0.9cm x 0.4cm), well-defined, ovoid mineral body. Craniomedially, the duct becomes indistinct.

• Surrounding the gland and throughout adjacent fascial planes is mild to moderate, wispy soft tissue resulting in ill-defined soft tissue margins.

• The left mandibular, retropharyngeal, and deep cervical lymph centers have numerous moderately enlarged, variably defined and rounded lymph nodes ranging in size (up to 2cm).

Post CT Ultrasound Images

Post CT US transverse image

Post CT US sagittal image

• Focused post-CT ultrasound documented a medium (1.1 x 0.3cm) mineral body within the thickened parotid duct; the duct is enlarged caudally and tapers rostrally.

• Severe left parotid salivary gland swelling, secondary to obstructive sialolithaisis (also identified on ultrasound)

• Suspect concurrent sialoadenitis and regional cellulitis

• Moderate left mandibular, retropharyngeal, and deep cervical reactive lymphadenopathy

 

• Aspiration of the swelling yielded grossly purulent material (subsequently cultured as actinomyces and mixed anerobic bacteria).

• Medical management: abscess drainage, antibiotic and anti-inflammatory administration, and lithotripsy.

• The patient was subsequently lost to follow up.

Discussion

Both sialolithiasis and septic sialadenitis occur most commonly in the parotid salivary gland (1,2), which is the largest paired salivary gland of the horse. The cause is unknown, but it is postulated that the close proximity of the parotid duct opening and the maxillary teeth may provide a mechanism for trauma by enamel points and/or entry point for foreign material (such as plant awn) (1). This hypothesis is supported by a study of 15 equids, in which 12/14 sialoliths had a nidus of plant awn and were primarily calcium carbonate (3). Multiple reports describe surgical approach to parotid sialoliths: intra-oral has better outcome than trans-cutaneous, the latter of which commonly results in fistulation (2,3).

 

References

1. Kilcoyne I et al, Septic silaoadenitis in equids: A retrospective study of 18 cases (1998-2010). Equine Vet Journal 2014;47:54-59.

2. Kay G. Sialolithiasis in equids, a report on 21 cases. Equine Vet Educ 2006;18(6):333-6

3. Oreff GL, Shiraki R, Kelmer G. Removal of sialoliths using the intraoral approach in 15 horses. Can Vet Journal 2016;57:647-650.