Atypical pulmonary metastases: Spectrum of radiologic findings

Typical radiologic findings of a pulmonary metastasis include multiple roun d variable-sized nodules and diffuse thickening of interstitium. In daily p ractice, however, atypical radiologic features of metastases are often enco untered that make distinction of metastases from other non-malignant pulmon ary diseases difficult. A detailed knowledge of the atypical radiologic fea tures of a pulmonary metastasis with a good understanding of the histopatho logic background is essential for correct diagnosis. Squamous cell carcinom a is regarded as the most common cell type of a cavitating metastasis, but metastatic nodules from adenocarcinomas and sarcomas also cavitate occasion ally. Calcification can occur in a metastatic sarcoma or adenocarcinoma, wh ich makes differentiation from a benign granuloma or hamartoma difficult. P eritumoral hemorrhage results in areas of nodular attenuation surrounded by a halo of ground-glass opacity. Pneumothorax commonly occurs in metastases from an osteosarcoma. Air-space consolidation is often seen in cases of me tastases from gastrointestinal tract malignancies. Even though tumor emboli in pulmonary arteries can be seen at computed tomography, diagnosis is dif ficult because they are located in small or medium arteries. A common radio logic appearance of an endobronchial metastasis is an atelectasis. In cases of an endobronchial or a solitary pulmonary metastasis, differentiation be tween bronchogenic carcinoma and metastasis is difficult. Dilated vascular structures within the mass can be seen in metastatic sarcomas. A sterilized metastasis after chemotherapy is radiologically indistinguishable from a r esidual viable tumor. Benign tumors such as uterine leiomyomas and giant ce ll tumors of the bone rarely metastasize to the lung.