Malignant fibrous histiocytoma of the deep peri-articular tissue of the stifle in a dog : case report

Abstract

A Belgian shepherd dog aged 4 years and 9 months was presented with acute onset of non-weight bearing lameness and stifle effusion of the left hind limb, caused by the deep form of a malignant fibrous histiocytoma originating in the deep musculature and fascia surrounding the stifle joint. The tumour progressed rapidly in the tissues along the femoral diaphysis with marked periosteal new bone formation. Cytology of a stifle joint aspirate revealed numerous large polygonal neoplastic cells with considerable anisocytosis and anisokaryosis. These cells were present in clusters, with cytoplasmic projections between the cells, but occasionally also occurred singly. Several cells contained multiple cytoplasmic vacuoles and occasional giant cells were also encountered. Adequate tumour-free margins were not possible with radical limb amputation and the dog was euthanased. Macroscopically the tumour appeared as an extensive pale tan, firm mass with scattered small haemorrhages and foci of yellow discolouration. Histologically the tumour consisted of dense neoplastic expanses or multiple nodules, composed of spindle-shaped fibroblastic cells, polygonal histiocytic cells or cell clusters and scattered giant cells with 2-3 nuclei. The polygonal neoplastic cells were frequently present around and invading lymphatics and blood vessels, causing neoplastic emboli. This is the 1st report of the clinical behaviour, radiography and cytology of the deep form of malignant fibrous histiocytoma in the dog.