Mastocytoma in a cow: a case report.

Mastocytoma was diagnosed in a four year old Holstein cow. The enlarging mass was clinically determined to be metastatic to the right superficial cervical lymph node. Cytological examination of both sites revealed mast cell neoplasia. Histopathological examination confirmed the presence of this tumor in these same sites as well as in liver, kidney and adrenal. Ultrastructurally, the mass contained round cells with electron dense granules in the cytoplasm.