[Leiomyoma of a kidney in a dog: a rare diagnosis]

A five-year-old, neutered male, Bernese Mountain Dog was referred because of a two-week history of hematuria and a one-week history of polydipsia and polyuria. Palpation of the dorsomedial mesogastrium revealed a mass on the left side, which was seen via radiography and ultrasonography to be attached to the left kidney. The left kidney and the attached mass were excised surgically, and the dog had an uneventful recovery. Histological examination of the mass revealed a dense proliferation of non-polymorphic spindle cells, which stained positive for smooth muscle actin via immunohistochemistry. Leiomyoma of the kidney was diagnosed. Postoperatively, there was mild azotaemia, which did not affect the general condition of the dog and was still present 15 months after surgery. Leiomyoma of the kidney is a benign tumor, and hematuria may be the only clinical sign.