Rare but Painful: Bilateral Zygomatic Sialadenitis in Dogs Mimics Orbital Disease

Canine bilateral zygomatic sialadenitis: 20 cases (2000‐2019)

A.E. Enache, S. Maini, M. Pivetta, E. Jeanes, L. Fleming, C. Hartley, R. Tetas Pont

Background
Bilateral zygomatic sialadenitis (BZS) is a rarely reported inflammatory condition of the zygomatic salivary glands in dogs. While unilateral cases have been described, bilateral presentations are uncommon, with limited data on clinical and imaging characteristics. This retrospective study aimed to characterize the clinical presentation, diagnostic imaging features, concurrent diseases, treatment, and outcomes in dogs diagnosed with BZS.

Methods
Clinical records from three UK referral institutions (2000–2019) were reviewed to identify dogs diagnosed with BZS based on clinical signs, cytology or histology, and imaging (MRI or CT). Inclusion criteria required evidence of bilateral zygomatic gland inflammation. Data collected included signalment, clinical findings, systemic diseases, diagnostic tests, treatment, and follow-up. Imaging findings were assessed for gland morphology, symmetry, enhancement patterns, and associated soft tissue involvement.

Results
Twenty dogs (mean age 7.1 years) met inclusion criteria, with Labradors comprising 50% of cases. Common signs included pain on mouth opening (90%), conjunctival hyperaemia (80%), exophthalmos (75%), and periorbital pain (75%). MRI and CT revealed symmetrically enlarged glands with heterogeneous contrast enhancement and hyperintensity on T1- and T2-weighted images. Myositis, cellulitis, and reactive lymphadenopathy were frequently noted. Cytology showed degenerate neutrophils in most cases, but bacterial culture was often negative. Fifteen dogs had concurrent systemic diseases, including skin allergies, hypertension, renal and gastrointestinal conditions, and neoplasia. Treatment primarily involved antibiotics (amoxicillin-clavulanate or clindamycin), anti-inflammatories (NSAIDs or corticosteroids), and supportive care. Clinical signs improved in 16/20 dogs, though 4 were euthanized due to unrelated systemic illness. Vision loss occurred in 4 dogs, attributed to orbital compartment syndrome or neoplasia, with partial recovery in some cases.

Limitations
The retrospective design limited standardization of diagnostic workups and follow-up. In some cases, definitive diagnosis was based on imaging and clinical response rather than cytology or histology. Sampling limitations and incomplete records may have affected case inclusion and interpretation. Concurrent systemic diseases may have confounded the assessment of treatment response and outcomes.

Conclusions
BZS should be considered in dogs with bilateral orbital signs and periorbital pain. MRI and CT provide critical diagnostic insights, showing characteristic gland enlargement and enhancement. Most dogs respond well to medical management, but complications such as vision loss or concurrent systemic disease can influence prognosis. Early recognition and targeted therapy are essential to avoid severe complications.

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