Calcified renal metastases: their etiology, pathogenesis, computed tomographic aspects and differential diagnosis

PURPOSE: To describe CT findings of calcified renal metastases focusing on differential diagnosis problems. MATERIAL AND METHODS: We retrospectively reviewed abdominal CT scans of 8000 patients with tumor, performed from 1984 to 1998. Among the 58 renal metastases, 9 showed a calcific component. We evaluated the location, morphostructural pattern, histology of the primary lesion, the synchronous or metachronous character and the type of treatment. All the lesions were pathologically proved. RESULTS: The primary histotype of the 9 metastases was as follows: 4 mucin-producing adenocarcinomas of the large bowel, 1 gastric mucinous adenocarcinoma, 1 chondrosarcoma, 1 osteosarcoma, 1 melanoma, 1 papillary thyroid carcinoma. In all the cases the renal metastasis was unilateral and unifocal. Granular multiple calcifications were demonstrated within the metastases of mucin-producing adenocarcinoma of the large bowel (3), within the metastasis of chondrosarcoma (1) and of melanoma (1). Diffuse "star-like" calcifications were demonstrated in renal metastases of mucin-producing adenocarcinoma of the large bowel and of gastric mucinous adenocarcinoma (1). Peripheral "egg-shell" calcifications were demonstrated in renal metastasis from papillary thyroid carcinoma (1). Completely calcified monofocal calcification was demonstrated in renal metastasis from osteosarcoma (1). DISCUSSION AND CONCLUSIONS: Calcified renal metastases are rare lesions related to specific oncotypes. The differential diagnosis (carcinoma with calcifications, osteosarcoma, chondrosarcoma, nephrocalcinosis, granulomatosis, hydatidosis etc.) is particularly difficult because of the aspecificity of the morphostructural pattern. Diagnosis is based on a history of specific oncotypes (papillary and mucin-secreting carcinomas, osteosarcoma and chondrosarcoma), but in most cases it requires pathologic confirmation.