An ultrasonographic renal parenchymal index.

A method for estimating the renal parenchyma relative to the whole kidney (renal parenchymal index, RPI) by ultrasonography has been developed. This method (the area of the sinus relative to the area of the whole kidney) was applied to sets of renal diseases. Hydronephrosis and fibrolipomatosis lead to enlargement of the renal sinus area. Changes in the proportion of parenchyma are small in chronic parenchymal diseases, but it often increases in thickness in acute cases and the RPI is consequently lower. The scars of chronic pyelonephritis reduce the size of the parenchyma in an irregular manner, and therefore measurement of the RPI is not as suitable in such cases as it is in other diseases, which involve generalized parenchymal changes. Because of the great normal variations the method is not suitable for diagnosis in single cases, but it is appropriate for basic surveys in which the relative changes in the renal parenchyma are being assessed in a large number of cases.