[Systematic program for the differentiation of cystic and solid lesions of the kidney].

Renal cysts are found in up to 50% of the population beyond 50 years. The coexistence of a renal cyst and a tumor is observed in 0.3% to 2.9% and may appear in 5 different types, of which type 2, the cysticly degenerated renal cell carcinoma, is most commonly found since 10% of the renal cell carcinomas reveal this phenomenon. Type 1, a renal cyst close to a renal tumor, is found in the literature in 5%; while the intracystic tumors (type 3 and 4) are rare with only 50 cases reported so far. The diagnostic procedures should reliably exclude malignant tumor. A differentiation between a simple renal cyst and malignancy is possible by intravenous pyelography and tomography alone in only 50%, while Catscan and angiography increase the accuracy to 93%. The sensitivity and specificity of ultrasonic examination is found to be 90%, whereas the combination of sonography and percutaneous cyst aspiration reaches an accuracy of 97%. A diagnostic exploration should be done only if the previous procedures are unclear.