[Hydronephrosis and peripelvic cysts. A new echographic sign for the differential diagnosis].

The differential diagnosis of peripelvic cysts and hydronephrosis by means of US sometimes presents some problems; in fact, the use of urography to solve a diagnostic doubt is not uncommon. This study was aimed at demonstrating that another US sign, which we have called the "convexity" sign, can be useful in allowing peripelvic cysts to be distinguished from hydronephrosis. Thus, cysts exhibit convex walls and curved outline, whereas in hydronephrosis the walls of the dilated calices are linear. The latter feature is present in all degrees of hydronephrosis, except in severe cases. Forty-nine adult patients, a total of 98 kidneys, were examined with US and urography; 69 kidneys were found to be pathologic: 48 presented with cysts, and 21 with hydronephrosis. In addition to the new sign, the classic signs of peripelvic cysts were also considered, that is the separate areas and the non-visualization of the ureter. The sensitivity of the new sign was 97% and its specificity was 95%. The sensitivity and the specificity of the classic signs were 97% and 95%, respectively for the separated areas, and 100% and 91% for the non-visualization of the ureter. The cumulative sensitivity of the 3 signs was 99%, and their specificity 96%. Our results show how the integrated analysis of the considered signs (especially those with high specificity) is useful for the differential diagnosis, and therefore to avoid the indiscriminate use of urography.