The utility of renal medullary pyramidal thickness measurements on the first and second postnatal ultrasound in infants with congenital hydronephrosis

Abstract

Introduction: Prior studies with postnatal ultrasound measurements of the medullary pyramid thickness (PT) demonstrate a PT < 3 mm as a significant risk factor for the diagnosis of UPJ obstruction and pyeloplasty. These studies used the postnatal ultrasound demonstrating the largest degree of hydronephrosis. Since early identification of children at increased risk of obstruction and pyeloplasty would be clinically useful, we reviewed the PT on the first and second postnatal ultrasound in infants with congenital hydronephrosis.

Objective: The aims of the study were to determine the prognostic value of: 1) PT on the first and second postnatal ultrasound, 2) a change in PT between first and second ultrasounds, and 3) ratio of PT in the hydronephrotic kidney to the contralateral PT in the normal kidney in those with unilateral hydronephrosis. We hypothesized that a smaller PT on either the first or second ultrasound, as well as a decreasing PT between the first and second ultrasound, and a decreased ratio of hydronephrotic PT to the contralateral normal kidney, would each be early predictors of subsequent pyeloplasty.

Study design: A retrospective chart and ultrasound review of children with a diagnosis of isolated high grade (SFU grade 3 or 4) hydronephrosis was performed. This study also analyzed the impact on predictive ability of the PT obtained on an ultrasound obtained before 3 days of life compared to those in which the first ultrasound was obtained after 3 days of life. 91 infants (77 boys and 14 girls) met eligibility criteria (105 kidneys). The median age (IQR) at first ultrasound was 1.5 (1.0-15.0) days and 54.0 (27.5-123.0) days at the second ultrasound.

Discussion and conclusion: For the group overall, a smaller PT on both the first and second ultrasound was associated with increased risk of pyeloplasty, however, a PT obtained on an ultrasound prior to 3 days of life was not demonstrated to be predictive. Of note, PT was predictive in this same group of patients on their second ultrasound. A PT of <3 mm on an ultrasound obtained beyond 3 days of life was associated with higher risk of pyeloplasty. The PT ratio of hydronephrotic to normal contralateral kidney of the children who had their first ultrasound after 3 days of life was also significant in predicting the odds of having surgery. In addition, a decreasing PT between the first and second ultrasound was also identified as a risk factor for pyeloplasty.

Keywords: Hydronephrosis; Pyeloplasty; Pyramidal thickness.