Spontaneous cyst rupture on renal CT

An 82-year-old man with anorexia and weight loss underwent an enhanced CT evaluation of the pancreas. The pancreas appeared normal, but the upper pole of the right kidney contained a sharply demarcated 5 x 3 x 4 cm mass with a uniform attenuation coefficient of 1 82 H (fig. 1A). The left kidney contained two small, typical, uncomplicated simple cysts with imperceptible walls, sharp demarcation, and fluid attenuation coefficients. Because the first examination had been performed only with contrast enhancement, CT was repeated 5 days later to evaluate the right renal mass further with and without intravenous contrast administration (1 50 ml Conray 60). There was no change in the size of the mass, but the attenuation coefficient measured 18 H, both before and after contrast enhancement (fig. 1 B). The appearances of the smaller left renal cysts were unchanged. The patient denied any episode of abdominal pain or hematuria during the 5-day interval. A subsequent renal mass puncture and aspiration was performed under fluoroscopic guidance after urographic localization of the right kidney with 1 00 ml Conray 400. The mass was cystic and yielded clear, yellow fluid that contained no malignant cells on cytologic examination. Spectrophotometric analysis, performed by the method of Medzihradsky et al. [2], failed to reveal any iodine in the cyst fluid. Doublecontrast examination showed a smooth inner lining of the cyst and no passage of air nor radiopaque contrast medium into the pyelocaliceal system. With these findings, it was believed that a cyst had ruptured into the right pyelocaliceal system before the first CT examination, and the resultant tract had closed before the second CT study.