Teaching Case

Woman, 47 years, abdominal pain of acute onset.

The patient was admitted with acute abdominal pain in the left hypochondrium. Chest X-ray [Fig. 1a] showed pleural effusion and abdominal X-ray [Fig, 1b] showed an abnormal opacity.

Laboratory tests revealed a slight increase in the protein-creatinine ratio (PCR >6).

Abdominal ultrassonography revealed slight hepatomegaly with homogeneous texture. In the left hypochondrium there was an expansive lesion with ill-defined boundaries, heterogeneous texture and gross calcifications.

The abdominal CT with i.v. contrast enhancement [Figs. 3a-g] revealed paramedian left abdominal bulky mass lesion with 20 x 16 x 12 cm, irregular and relatively well- defined borders, predominance of solid points, as well as amorphous calcifications.

This lesion was pushing the left kidney establishing no cleavage planes, supporting the hypothesis that the kidney would be the organ of origin.

Selective embolisation was performed and then surgical resection was performed.

The pathologic study revealed an extra-skeletal osteosarcoma of the kidney [Figs. 4a-e].

Unfortunately, the patient died shortly after surgery.

Primary renal osteosarcoma is an extremely rare tumour. Its cell type of origin
is undifferentiated mesenchymal cells of the kidney. One of the typical characteristics
is extensive ossification in a “sunburst” pattern, sometimes viewable
in routine radiographs. However, one should consider other possible diagnoses, including the sarcomatoid variant of renal cell carcinoma and osteogenic sarcoma with metastasis to the kidney which may also contain ossification [2].
Radiographic differentiation of these three malignancies is difficult and, sometimes, only a pathologic study allows their differentiation.
The presence of renal tumour ossification makes the hypothesis of osteogenic sarcoma of the bone with kidney metastasis more likely than primary renal osteosarcoma because the first one is by far a more common malignancy.
Elevated alkaline phosphatase levels is a good method of differentiating between
primary renal osteosarcoma and metastatic osteogenic sarcoma of the kidney when a calcified renal tumour is found in the absence of a clinical history of a primary tumour.
Microscopically, the tumours contain varying amounts of neoplastic osteoid and bone, sometimes together with islands of malignant-appearing cartilage. Like osteosarcoma of bone, extraskeletal osteosarcoma show a striking variation in histological appearance and focally resembled malignant fibrous histiocytoma, fibrosarcoma, and malignant schwannoma. The prevailing sites of metastases are the lung, the regional lymph nodes and bone.
The prognosis is extremely poor (mean survival, 8-22 months) despite an aggressive therapeutic approach including radical nephrectomy, radiation and chemotherapy [3, 4]