Glomus tumour in the digit of a dog.

The gross and microscopical features of a glomus tumour in the digit of a 9-year-old dog are described. The tumour consisted of a red nodule near the nail of the third digit of the right forelimb and appeared painful. The tumour cells, which had round to oval hyperchromatic nuclei and scant cytoplasm, were arranged in sheets around blood vessels, or in nests or duct-like structures. This pattern has not been described previously in canine glomus tumours. Mitotic figures were seen only occasionally. Tumour cells were strongly immunolabelled for vimentin and some expressed smooth-muscle actin and desmin. They were negative for cytokeratins, neuron-specific enolase and CD34. Silver impregnation (reticulin method) stained the reticulum around blood vessels, nests of tumour cells and duct-like structures, and a delicate reticulum was seen around each tumour cell. The morphological, immunohistochemical and histochemical patterns helped in the diagnosis of this glomus tumour.