*Rafael Rivas, Dolores I. Ginel, Victoria Ramírez, Pedro J. Ginel
A 7 month-old male German shepherd was presented because of marked swelling affecting the flexor muscles of the right hindlimb. The dog was in good body condition and no systemic signs were found. On palpation, the mass was well delimited, moderately painful and soft but with high tension suggesting a fluid-filled cavity. There was edema distal to the lesion but lameness was slight.
A traumatic origin was suspected and initial treatment consisted on oral diuretics and antiinflammatory doses of prednisone. After five days of treatment the size of the mass was not reduced and a fine needle aspiration obtained a serosanguineous exudate. Radiographic examination of the lesion showed peripheral calcification. Penrose drainage was placed and, as the lesion seemed to have well delimited walls, surgery was advised.
At surgery, the mass was completely included within the femoral biceps muscle and was well irrigated which made extirpation difficult and created a severe muscular defect with hyperextension of the common flexor tendon. The limb adopted a plantigrade position that 1.5 months after the surgery seems to be improving as the femoral biceps recovered part of its muscular mass.
Our aim was to describe, the clinical and pathological signs of a dog with a calcified cystic mass arising from the biceps femoral muscle. Clinically, main differential diagnosis of this type of calcified lesion in the dog were calcinosis circumscripta and fibrodysplasia ossificans recently described in the German shepherd dog. Histopathologically, the lesion was compatible with a traumatic origin and lacked any particular or specific feature. It was composed by a reactive fibrous tissue, arranged perpendicularly to the central cavity, and with a well-developed collagenic stroma scattered by areas of mineralization and some foci of osteoid metaplasia. However, clinically the lesion strongly resembled human calcific myonecrosis. This is a rare syndrome characterised by a expansile, calcified cystic mass that develops in muscles after trauma. Common features were the muscular location, the probable traumatic origin, the replacement of muscular tissue by the calcified mass, the peripheral arrangement of the calcification in a thin linear pattern, the cystic nature and the cholesterol-rich haemorrhagic content. In contrast, after initial injury calcific myonecrosis has a expansion course of years or decades, whereas in this dog expansion of the mass could not take more than several weeks.