🦷 New Insights into Equine Jaw Cysts: Study Identifies Diagnostic Patterns and Outcomes in 17 Horses

Equine Maxillofacial Intraosseous Cystic Lesions: A Retrospective Study of 17 Cases

Jennifer L. Kelley, Jennifer E. Rawlinson, and Cynthia M. Bell

Background

Cystic and pseudocystic lesions of the equine maxilla and mandible are rare but clinically significant causes of facial swelling, nasal discharge, and dental abnormalities. Prior reports have been limited to single cases, leaving uncertainty around classification, treatment, and outcomes. This retrospective study aimed to characterize the clinical, imaging, histopathologic, and surgical features of equine intraosseous cystic lesions to improve diagnostic accuracy and therapeutic planning.

Methods

Medical records from six institutions (2017–2022) were reviewed to identify horses with cystic or cavitated lesions in the incisive, maxillary, or mandibular bones. Inclusion required diagnostic imaging, histopathology, and follow-up data. Primary sinus cysts and teratomas were excluded. Clinical, radiologic, and histopathologic data were correlated to classify lesions as dentigerous cysts (DTC), radicular cysts (RC), bone cysts (BC), or unclassified inflammatory lesions (UIL). Most horses underwent surgical excision or debridement, and follow-up ranged from 0 to 872 days.

Results

Seventeen horses met inclusion criteria (median age 8 years, range 0.75–36). Lesions were most common in the mandibular body (8/17), followed by the caudal maxilla/sinuses (5/17), rostral maxilla (4/17), and rostral mandible (2/17). Diagnoses included 6 dentigerous cysts, 6 bone cysts, 3 radicular cysts, and 2 unclassified inflammatory lesions.

-Facial swelling (76.5%) and unerupted or missing teeth (41.2%) were the most frequent clinical signs.

-Radiographic findings revealed tooth involvement in 94% and multiloculated lesions in 82% of cases.

-Histopathology confirmed epithelial lining in cystic lesions, with dentigerous cysts showing stratified squamous or odontogenic epithelium, while bone cysts displayed pseudocystic fibrovascular tissue with macrophages and giant cells.

-Treatment consisted mainly of surgical excision and debridement; one case required rostral mandibulectomy.

-Outcomes: 65% (11/17) had no recurrence, and complications (35%) included fistula formation and postoperative sinus issues.

Limitations

The study was retrospective and limited by small sample size, non-standardized imaging and histopathologic protocols, and variable follow-up durations. The heterogeneity of diagnostic methods may have influenced lesion classification accuracy.

Conclusions

Equine intraosseous cystic lesions, though rare, can be effectively diagnosed through integration of clinical signs, imaging, and histopathology. Surgical excision and debridement yielded favorable outcomes in most cases. Dentigerous and bone cysts were the most prevalent types, with mandibular lesions predominating. This study underscores the need for consistent diagnostic criteria and long-term monitoring to better understand recurrence risk and pathogenesis.

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