Abstract
An eleven year-old mongrel dog was referred with a history of left forelimb lameness and an ulcerated mass on the neck. Histologically, the cutaneous neoplasm revealed cystic lobules composed of basaloid cells with abrupt transition to central keratotic material, containing pycnotic and shadow cells. Approximately 3 months after primary diagnosis, a lesion of the cortical bone on the left humerus was observed using X-ray. Samples obtained from the humerus were processed for histopathological examination and the neoplastic tissue was observed to be similar to the type identified in the neck. Based on these findings, the tumor was diagnosed as a malignant pilomatricoma (MP) with bone metastasis. MP is a rare skin tumor that originates from hair matrix cells. To date, only nine reports have been presented in dogs. In the present study, we discuss the cytological and histological patterns of MP, confirmed by immunohistochemistry using β catenin antibody.
Highlights
Pilomatricoma is a benign adnexal neoplasm with follicular differentiation similar to matrical cells of the hair bulb, which occurs in middle-aged to older dogs (2-7 years of age) with normal gender distribution [1,2,3,4,5]
An abrupt keratinization from basaloid to shadow cells is characteristic of this neoplasia [3,5]
The criteria for malignancy in the differential diagnosis between malignant pilomatricoma (MP) and its benign counterpart are the presence of an encapsulated asymmetric ulcerated tumor growth, increased mitotic figures with nuclear atypical features, infiltration of the adjacent skin and lymphatic invasion at the periphery of the mass [3,7,8]
Summary
Pilomatricoma is a benign adnexal neoplasm with follicular differentiation similar to matrical cells of the hair bulb, which occurs in middle-aged to older dogs (2-7 years of age) with normal gender distribution [1,2,3,4,5]. Cytological examination of samples obtained by fine needle aspiration showed small cohesive epithelial aggregates composed of basaloid cells, a small amount of amorphous keratinized material and a few ghost cells. Due to these findings, an initial diagnosis of a follicular tumor with matrical differentiation was made. Upon microscopic examination, performed following the routine procedure for decalcification, a neoplasia similar to the type identified in the primary skin mass was observed. Compared with the primary tumor, there were larger areas of necrosis and a greater proportion of basaloid cells, which showed more severe atypical features. Due to the extremely poor prognosis, euthanasia but not necropsy was permitted by the owner
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