Myxomas and
myxosarcomas are infiltrative connective tissue
tumors of fibroblastic origin that can be distinguished by the presence of abundant mucinous stroma. This paper describes the clinical and imaging features of orbital
myxosarcoma in five dogs and suggests a predilection for the orbit. The main clinical signs were slowly progressive
exophthalmos with soft swelling of the pterygopalatine fossa, and in two dogs, of the periorbital area. No
pain was associated with the eye or orbit but one dog had
pain on opening the mouth. The dogs were imaged using combinations of ultrasonography, radiography, and magnetic resonance imaging. In four dogs, extensive fluid-filled cavities in the orbit and fascial planes were seen and in the fifth dog, the
tumor appeared more solid with small, peripheral cystic areas. In all dogs, the lesion extended along fascial planes to involve the temporomandibular joint, with
osteolysis demonstrable in two dogs. Fluid aspirated from the cystic areas was viscous and sticky, mimicking that from a salivary mucocoele.
Myxomas and
myxosarcomas are known to be infiltrative and not readily amenable to surgical removal but their
clinical course seems to be slow, with a reasonable survival time with
palliative treatment. In humans, a juxta-articular form is recognized in which a prominent feature is the presence of dilated,
cyst-like spaces filled with mucinous material. It is postulated that orbital
myxosarcoma in dogs may be similar to the juxta-articular form in man, and may arise from the temporomandibular joint.