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Background:
The mercaptoacetyltriglycine scan remains the current gold standard for assessing the obstructive nature of hydronephrosis in children. Unfortunately, this study requires intravenous administration of radiolabelled agents, and a diuretic while remaining still under a gamma camera - sometimes requiring sedation. Advanced ultrasonography technology combined with computational analysis may allow for a less invasive modality to assess for renal obstruction. We applied a novel method to evaluate static renal sonograms, pre and post-pyeloplasty, to measure the heterogeneity observed in the renal cortex as an index of obstruction.
Methods:
We examined the levels of heterogeneity in pre and postoperative sonograms of renal units of children with hydronephrosis secondary to surgically confirmed ureteropelvic junction obstruction (UPJO) and compared them to each other and to the contralateral unaffected kidney. Pyeloplasty were performed either open or robotically using the dismembered technique. Representative static mid-sagittal ultrasound images of the affected kidneys and their normal contralateral kidneys were examined using a novel program. We then measured the pixels of a gray-scale ultrasound image and transformed them into a binary map to determine heterogeneity index (HI) values and the dynamic range (DR) of each ultrasound image. The investigators were blinded to the status of each kidney. Regression analysis was used to determine the Pearson correlation and linear functional association between the HIs.
Results:
Twenty-five obstructed kidneys from children with a mean age of 55 months (range 5-144) were identified and the heterogeneity of their sonograms assessed. The preoperative images were within 1 month of surgery while the post-operative images were obtained on average 4.5 months after surgery. Pre-operative MAG-3 scans demonstrated an average differential renal function of 42% and obstruction evidenced as absent post-furosemide drainage (8 kidneys) or t½ >20 minute (17 kidneys). Postoperative scans were avoided given the low grades of hydronephrosis (mode, SFU grade 2). The DR analysis of the mid-sagittal region of the contralateral, pre- and post-pyeloplasty, indicate an improvement in heterogeneity post pyeloplasty. We measure an average percent error 34.4% between pre-pyeloplasty and contralateral kidneys versus 3.17% between the post-pyeloplasty and contralateral kidneys. Regression analysis demonstrated no correlation between pre-pyeloplasty HI and contralateral HI (r=0.049, p=0.288) or between pre-pyeloplasty HI and post-pyeloplasty HI (r=0.035, p=0.368); however, post-pyeloplasty and the contralateral HI values did significantly correlate (r=0.168, p=0.042). This novel method discovered a hyperechoic trend in obstructed hydronephrotic kidneys pre-pyeloplasty compared to healthy kidneys while post-pyeloplasty kidneys demonstrated more of a normalization of echogenicity following surgery.
Conclusion:
We have developed a novel non-invasive method to detect differences in parenchymal heterogeneity of obstructed and non-obstructed kidneys in children. These dynamic range index changes demonstrated a significant trend towards normalization post surgical intervention. These novel findings, using non-invasive measurements, may lead to paradigm shifts in how we assess and follow hydronephrosis in pediatric urologic patients.