CASE HISTORY: A 5-month-old valuable Red Holstein bull presented with a cutaneous mass on the fetlock of the right hind limb. The mass was removed and histologically diagnosed as a benign angiomatosis. Four months later, the mass reoccurred on the same leg.
PATHOLOGICAL FINDINGS: The first excision biopsy consisted of numerous blood vessels of different diameters and wall thicknesses. Often, the smaller vessels were oriented around a larger, vein-like vessel. The endothelial cells were elongated with small oval to elongated nuclei with dense chromatin. Following recurrence, the mass showed clear signs of infiltrative growth, including solid bundles of cells, increased polymorphism and round to oval nuclei with coarse chromatin and distinctive nucleoli. The neoplastic cells were immunohistochemically positive for von Willebrand Factor (vWF).
DIAGNOSIS: Angiomatosis with focal progression to an infiltrative growing sarcoma-like tumour.
CLINICAL RELEVANCE: This case represents the progression of a benign vascular proliferation, often considered as a reactive process, into a more aggressively behaving neoplasm. The clinical behaviour and histopathological morphology were strikingly similar to previous cases described in human and veterinary medicine.