WN von Sinner, Hydatidosis Mimicking Metastases. 1992; 12(3): 316-320 In three cases hydatid cysts were initially misdiagnosed as metastases. A case of biopsy-confirmed hypernephroma showed multiple bilateral rounded densities in the lungs suggesting metastatic disease. A second case with cystic expansive lesion of the liver clinically diagnosed as "cystic hepatocellular carcinoma" was combined with multiple bilateral "nodules" of the lungs mimicking metastases. A third case with biopsy-confirmed hypernephroma demonstrated multiple hepatic lesions thought to be metastases. Computed tomography (CT) was helpful in disclosing these low density lesions as hydatidoses.The recognition of a malignant tumor coexistent with hydatid disease is important for appropriate and effective treatment both of the malignant tumor and the parasitic infection. Today, powerful benzimidazole compounds make successful chemotherapy treatment feasible even in widespread or disseminated hydatid disease. Recognition of these lesions is, therefore, crucial for potential cure.Ultrasonography (US) computed tomography (CT), and magnetic resonance imaging (MRI) have, to a large extent, replaced less effective and invasive methods. Alone or in combination with each other, they are helpful in assessing uni-or multilocular lesions throughout the body, including the lungs [1][2][3][4][5]. Hydatidosis and tumor may look very similar [6,7]. In cases where extrapulmonary malignant tumor has been confirmed by biopsy, the occurrence of multiple rounded densities in the lungs are usually interpreted as metastases. Even without a known primary tumor, multiple hydatid cysts in other organs or tissues may closely resemble neoplastic deposits and be confused with metastases. Their recognition is, therefore, extremely important for appropriate therapeutic management as a precondition for cure [8]. Case Reports Case 1In a 51-year-old man, a space-occupying lesion of the left kidney was discovered. A CT of the abdomen and kidneys (Figure la) confirmed the presence of a 13 cm in diameter large mass of the left kidney with irregular density and a tiny area of calcification. No evidence of lymphadenopathy or extrarenal extension was found. A fine needle aspiration biopsy revealed a renal cell carcinoma. On the preoperative chest radiography, two rounded bilateral densities in the lower lobes were seen (right 2.5 cm and left 6 cm in diameter) thought to be metastases. It was therefore assumed that the patient was inoperable. CT of the chest, however, showed that the lesions were cystic. Since the density was between 10 and 20 HU, infected cysts or hydatid disease (Figure lb) could not be excluded. Serological examinations revealed very high echinococcal titers (IHA 1:2, 048; normal values up to 1:32) confirming the presence of hydatid disease. A radical left nephrectomy was, therefore, still possible and carried out before renal metastases had developed. Case 2A 46-year-old man suffered from shortness of breath for three years, weight loss and cough. In the past...