Congenital mesoblastic nephroma in a young basset hound dog

An 18‐month‐old male basset hound was presented with vomiting, diarrhoea and depression. Abdominal ultrasonography revealed a mass in the left kidney. An ultrasound‐guided core‐biopsy indicated aggregates of spindle cells, but did not allow a definitive diagnosis. Nephrectomy was performed after a period of six months, when ultrasound examination revealed a slight increase in mass dimensions. Histologically the mass was composed of neoplastic spindle cells forming interlacing fascicles, bundles and whorls, within a loose myxoid to dense collagenous stroma. Immunohistochemically neoplastic cells were positive for vimentin and smooth muscle actin. Based on these findings the tumour was diagnosed as a congenital mesoblastic nephroma, classical variant. After a two‐and‐a‐half‐year follow‐up the dog was clinically healthy, indicating a benign behaviour. To the authors’ knowledge, this report describes the first case of canine congenital mesoblastic nephroma successfully treated surgically, with a reasonable postsurgical follow‐up.