Matrix "blues": clue to a cranial thoracic mass in a dog.

A 5-year-old, intact male Italian Spinone dog was presented for progressive, severe dyspnea and coughing. Thoracic radiographs revealed a large mass in the right cranial thorax. Fine needle aspiration of the mass yielded a highly cellular sample containing dense clumps of oval to spindle-shaped mesenchymal cells with distinct intracytoplasmic vacuolation, consistent with lipoblasts and lipocytes. Cell clusters were associated with abundant eosinophilic matrix, which was identified as mucin, based on Alcian blue staining. At exploratory thoracotomy, the mass was found to be nonresectable, and the dog was euthanized. Histologic sections of the multilobular mass had discrete regions of variable cellular differentiation, including highly cellular areas of pleomorphic cells, areas of spindle cells and lipoblasts in a myxoid background, and areas of well-differentiated lipogenic cells. The histologic diagnosis was myxoid liposarcoma. The thoracic cavity is a rare site for liposarcoma in the dog. The cytologic features of lipoblasts together with a mucopolysaccharide matrix were useful for distinguishing the myxoid variant of liposarcoma from other forms of liposarcoma and myxoid sarcomas.