Ectopic ossification presenting as osteoid metaplasia in a salivary mucocele in a Shih Tzu dog

A right facial enlargement was suddenly observed in a 4-year-old non-spayed female Shih-Tzu dog. The lesion presented itself as a soft and fluctuant mass located in the right side of the face near to the neck. Histologically, the mass consisted of a cavitary formation without an epithelial lining. Additionally, microscopic examination revealed the presence of osteoid-producing cells which gave rise to areas of bone formation, probably induced by irritation due to the presence sialoliths. Such cells and bone formations were also present in the cavity wall, consequently leading us to classify the condition as a salivary mucocele with osseous metaplasia.In the present case, the pathogenesis was probably associated with the presence of sialoliths, which can behave as etiological agents for the metaplastic lesion. The occurrence of osteoid metaplasia is a rare peculiar condition in the canine salivar y gland, and due to the rarity and lack of information about this specific disease, no clinical data can yet be associated with the development of salivary mucocele with osseous metaplasia in dogs.Salivary gland disorders are uncommon diseases of dogs, with an overall reported incidence of less than 0.3 percent [1]. Salivary mucocele in an accumulation of saliva in a single or multiloculated cavity lined by connective tissue [2]. This cavity is contiguous to a salivary gland-duct complex [3] and is the most common condition affecting the salivar y glands in dogs [4]. Salivary mucoceles can reveal differentiation in several types of tissues, such as those represented by squamous [5] and osseous metaplasia [6,7]. There are only two reported cases of osteoid metaplastic salivary mucocele in the dog [6,7], none of them in the Shih Tzu breed. Accordingly, the aim of this article is to describe a case of this rare variation of salivary mucocele in a female Shih Tzu dog.A 4- year-old, non-spayed female Shih-Tzu dog was admitted to the School of Veterinar y Medicine and Animal Scien