Ureteropelvic Junction Obstruction Affects the Contralateral Kidney: A Novel Investigation of Sonographic Heterogeneity
Bradley A. Morganstern, MD1, Wayland Wu, MD1, Vinaya Vasudevan, MD1, Matthew Elsmari, BS1, Megan Murphy, None2, Sleiman R. Ghorayeb, PhD2, Lane S. Palmer, MD1.
1Cohen Children's Medical Center of New York, Hofstra Northwell School, New Hyde Park, NY, USA, 2Departments of Radiology and Molecular Medicine, Hofstra Northwell School of Medicine, Hempsted, NY, USA.
We developed and previously reported a novel non-invasive method to detect differences in parenchymal heterogeneity of obstructed and non-obstructed kidneys in children. The changes of sonographically detected heterogeneity demonstrated a significant trend towards normalization post-surgical intervention and holds true when specifically comparing post-op stented kidneys compared to follow-up imaging without a stent. These findings may alter assessment and follow-up of hydronephrosis in children. Noting differences in the kidney undergoing a pyeloplasty, we sought to evaluate if the contralateral kidney could serve as an intrinsic control for subsequent sonographic evaluations.
Representative static transverse sonographic images were examined using a novel program where the pixels of a marked range of interest of gray-scale images of the cortex were transformed into a binary map to determine heterogeneity index (HI). Using a linear mixed model, HI was analyzed as a function of group: pre-surgery, post-surgery or normal control. A mixed models approach was then used to account for the hierarchical structure of the data; namely, each pyeloplasty subject was age-matched to two normal (non-pyeloplasty) controls and within each pyeloplasty subject by measuring the HI of both the affected and contralateral unaffected kidneys pre and post-operatively. Upon finding a significant association between group and HI, pairwise comparisons were conducted using the Tukey-Kramer method to determine which groups differed significantly from each other.
There were 58 pyeloplasty subjects with a total of 116 measures (58 contralateral pre-surgery and 58 contralateral post-surgery). Pyeloplasty subjects were age-matched to two normal controls. There were two pyeloplasty subjects that were age-matched to only one normal control, which resulted in a total of 114 normal controls. The groupings of subjects were significantly associated with HI (p < 0.0001). Specifically, pre-surgery HI in contralateral kidneys was significantly higher than post-surgery HI, either mean 50 days (prior to stent removal) and mean 131 days post-surgery, in contralateral kidneys (p = 0.0085). HI in normal controls was significantly lower than pre-surgery contralateral kidneys (p < 0.0001) and post-surgery contralateral kidneys (p = 0.0202) (Figure 1). There was no difference between the post pyeloplasty kidney HI and the HI of contralateral kidney (p<0.79), meaning surgically correcting the obstructed side normalizes it to the contralateral kidney but not necessarily to patients without renal abnormalities.
Obstruction of one renal unit causes sonographically detectable changes in heterogeneity of the contralateral kidney that significantly decreases upon relief of the obstruction. These changes in heterogeneity of the contralateral kidney may represent potentially reversible physiological changes occurring due the other renal unit being obstructed, such as hyperfiltration or intrinsic damage, and that require further investigation. Currently, the contralateral kidney should not be utilized as a true control compared to norms for assessing changes in the obstructed kidney but may serve a relative metric for subsequent follow-up imagining.
Figure 1: Mean HI of Groupings
|Group||Mean HI (95% CI)|
|Contralateral Pre-Surgery||1.28 (1.24, 1.32)|
|Contralateral Post-Surgery||1.22 (1.18, 1.25)|
|Normal controls||1.15 (1.13, 1.18)|
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