Sonographic renal parenchymal and pelvicaliceal areas: new quantitative parameters for renal sonographic followup

We determined better quantitative parameters for renal sonography and applied these parameters to the evaluation and followup of prenatal hydronephrosis.

We retrospectively reviewed normal renal ultrasound studies of 120 children and serial ultrasound studies of 40 with prenatal hydronephrosis. Renal length, bipolar parenchymal thickness and anteroposterior pelvic diameter were measured from serial sonograms of patients with hydronephrosis. Renal longitudinal parenchymal area and renal longitudinal pelvicaliceal area were determined from the sonograms of normal children and from serial studies of patients with hydronephrosis using computer planimetry. Data from normal children were plotted to construct a renal parenchymal area growth chart. Length and area measurements were compared using regression analysis. The ability of these parameters to predict patients who would require pyeloplasty was examined.

Normal parenchymal area correlated well with normal renal length (r2 = 0.92). Differential parenchymal area correlated with differential function (r2 = 0.75), while differential length and bipolar thickness correlated poorly with function (r2 = 0.01 and 0.42, respectively). The ratio of parenchymal-to-pelvicaliceal area differentiated patients with unilateral hydronephrosis requiring pyeloplasty from those treated conservatively. The ratio was less than 1.6 in all patients requiring pyeloplasty and greater than 1.6 in those followed conservatively.

Renal parenchymal area provides a more accurate estimate of renal size and function in the hydronephrotic kidney than traditional 1-dimensional measurements. In our limited series the ratio of renal parenchymal-to-pelvicaliceal area allowed the prediction of patients who required pyeloplasty.