Necropsy examination of the animal revealed a large, cystic, perihepatic mass. Cytoplasmic granules appeared red and slightly elongate, suggesting heterophilc cell lineage. The neoplasm also contained numerous variably sized and shaped vascular spaces. More normal sections of liver contained scattered foci of extramedullary heterophil production, often centered around blood vessels beneath the hepatic capsule. Perihepatic mass appears hypercellular.
More differentiated cells contain red cytoplasmic granules.
Electron microscopy of ultrathin sections of the mass revealed two types of neoplastic cells. The first cell type consisted of large, round blasts with a thin rim of cytoplasm containing occasional granules. The second cell type appeared smaller, round , and more differentiated. The cytoplasmic granules were round in cross section and elongated in longitudinal section. These ultrastructural characteristics were typical of heterophilic lineage.