Metastasis of adenocarcinoma of an unknown primary site to the right crus simulating sarcoma - a case report.

: More bony malignancies are metastatic than primary tumours. Usually, it is not difficult to distinguish a metastasis from a primary tumour; however, when the metastasis is the first manifestation of malignant disease, diagnosis may cause numerous difficulties and lead to therapeutic errors. A patient with one year's history of pain in the right crus who was initially suspected of having sciatica and venous thrombosis was referred to an orthopaedic department when radiographs of the crus were suspicious for an osteosarcoma. CT and MRI scans revealed a tumour originating in the proximal fibula with numerous periosteal reactions. A biopsy indicated metastatic adenocarcinoma. Further diagnostic examinations didn't reveal the primary tumour. A PET scan showed a small pulmonary nodule of unknown aetiology. The patient underwent limb-sparing surgery followed by chemotherapy. The diagnostic work-up of bony malignancies may pose difficulties. Despite a characteristic presentation of sarcomas of bone in imaging examinations, it may be impossible to distinguish metastases and primary tumours. This problem especially concerns patients in whom metastases are the first manifestation of malignant disease and imaging examinations show no abnormalities in internal organs. Histopathological evaluation should be mandatory for all bone tumours which are not confirmed metastases before any therapeutic decisions are made. One must be aware of limitations and errors related to diagnostic work-up in oncology, including histopathological examinations. Sometimes it may be impossible to obtain a result of microscopic analysis compatible with the clinical presentation.