An ultrastructural study of vulval myofibroblastoma in a cow.

A case of myofibroblastoma in a 3-year-old Japanese Black cow is described. Raised tumours which formed in the anus and in the labium and vestibulum of the vulva during pregnancy were excised surgically. The latter two tumours had dense growth of slender spindle cells beneath the epithelium, and fibrous connective tissue at the periphery. The anal tumour consisted of abundant collagen and sparse numbers of spindle cells. Proliferating cells contained moderate amounts of thin filaments with focal densities as well as well-developed rough endoplasmic reticulum and Golgi apparatus, and desmosome-like structures were found between the cells. These cells were distinguishable from leiomyoma cells containing abundant thin filaments and poorly-developed organelles. In the neoplastic lesions, there was an infiltration of many lymphocytes, plasma cells and macrophages.