Mandibular Periostitis Ossificans in a 17-Week-Old Male Great Dane.

This case report describes the clinical, radiographic, and histopathological features of a self-limiting mandibular swelling in a juvenile, large breed dog with a diagnosis of mandibular periostitis ossificans (MPO). This is a pathologic syndrome of immature large breed dogs that presents with a unilateral, nonpainful, caudal mandibular swelling centering on the erupting first molar tooth. This condition affects dogs with a median age of approximately 4 months. The diagnosis of MPO, in this case, resulted from the assimilation of clinical and radiographic findings, along with woven bone proliferation on histopathology. A distinct "double cortex" seen on radiographs of the caudal mandible is a defining characteristic of MPO that is most likely due to an additional cortical bone layer being produced on the mandible. MPO spontaneously resolved indicating that treatment with benign neglect was successful. The pathogenesis of periostitis ossificans is likely to be multifactorial and the mandibular bone of young, large breed dogs appears to be intrinsically predisposed. Trauma, occlusal forces, and foreign bodies are considered risk factors in the development of MPO. In this case report, trauma from a previous bite wound when the dog was 9 weeks old was a risk factor for this dog in developing MPO.