# Correlation of Hydronephrosis Index to Society of Fetal Urology Hydronephrosis Scale

Authors: Krishnan Venkatesan; Joel Green; Steven R. Shapiro; George F. Steinhardt
Journal: Advances in Urology
 (2009)

---

## Abstract

Purpose. We seek to correlate conventional hydronephrosis (HN) grade and hydronephrosis index (HI). Methods. We examined 1207 hydronephrotic kidneys by ultrasound.  HN was classified by Society of Fetal Urology guidelines. HN was then gauged using HI, a reproducible, standardized, and dimensionless measurement of renal area. We then calculated average HI for each HN grade. Results. Comparing HI to standard SFU HN grade, average HI is 89.3 for grade I; average HI is 83.9 for grade II; average HI is 73.0 for grade III; average HI is 54.6 for SFU grade IV. Conclusions. HI correlates well with SFU HN grade. The HI serves as a quantitative measure of HN.  HI can be used to track HN over time.  Versus conventional grading, HI may be more sensitive in defining severe (grades III and IV) HN, and in indicating resolving, stable, or worsening HN, thus providing more information for clinical decision-making and HN management.


---

## Body

## 1. Introduction

Ultrasound (US) has gained
widespread acceptance and use in fetal and pediatric urology.Hydronephrosis (HN) has become the most common abnormality detected by prenatal
US [1]. HN had previously been characterized in a fairly subjective manner as mild, moderate, and severe. In 1993, the
Society for Fetal Urology (SFU) established a grading system based on renal
sinus splitting patterns and dilation of the renal pelvis and calyces [2]. Though the SFU grading system has been widely
accepted, it does have certain deficiencies—especially in
differentiation of severe (grades III and IV) HN [3]. Serial assessment of HN
by US, often used in clinical decision making, relies on this grading system to
suggest improving, stable, or worsening HN. Others have suggested improvements
or complementary approaches to the SFU grading system [3–5]; none has gained widespread
popularity of use.Recently, a novel method to measure
HN was suggested. The Hydronephrosis index (HI) has been shown to be a
quantitative, reproducible, standardized measure of HN [6]. HI is calculated as a dimensionless number
that represents renal area and can be used for serial examination of kidneys
with HN. The present work serves to
correlate the SFU grading system with the HI system, to advance familiarity
with this new method of HN description.


## 2. Materials and Methods

An IRB approved prospective,
computerized database accrued by the authors (George F. Steinhardt, Steven R.
Shapiro) at their previous institution, was queried for all kidneys with the
diagnosis of ureteropelvic junction obstruction (excluding kidneys with
concomitant vesicoureteral reflux or sonographic ureteral dilation). All of these 1207 kidneys were then assessed
using both the SFU grading system and the HI technique. The managing pediatric
urologist (George F. Steinhardt) determined the SFU grade (I–IV) of HN; the
pediatric radiologists, supervising the sonographic technician, determined HI.
Studies were performed using an Acuson Sequoia 512 system (Siemens Medical
Solutions, Malvern, Pa,
USA).Specifically, a single sagittal US
image was selected, where the kidney achieved its maximal longitudinal dimensions. The operator then
marked the renal boundaries, traced an outline of the entire renal perimeter
and then of the dilated renal pelvis (Figure1). The portion of the renal pelvis extending
beyond the kidney was not included in the HI [6]. The respective areas were
then computed with integrated software which is standard on most modern
ultrasound machines.Figure 1
Boundaries of hydronephrotic kidney
marked.Data was entered into the database
as patients were managed in the office.HI is calculated as follows: HI
(percentage) = 100× (total area of the kidney minus area of dilated pelvis)/(total
area). The result is a quantitative,
dimensionless measurement of renal mass. In essence, HI represents the
percentage of total kidney that is renal parenchyma.For each grade of hydronephrosis,
the average HI was calculated.


## 3. Results

The average HI was calculated for
each group of kidneys, in order to establish a correlation of HI to HN grade
(Table1). The number of kidneys in each group is also listed in Table 1.Table 1
Correlation of HI to HN grade.
SFU gradeMean HIRange of HIHI std devNumber of kidneysI89.342–975.9202II83.939–1007.2444III73.043–978.6298IV54.620–9412.5263A normal nonhydronephrotic kidney
would have an HI of 100. More
hydronephrosis, or renal pelvis dilation, translates to a larger renal pelvic
area and thus, a lower HI. For the group
comprised of kidneys with grade I hydronephrosis, the average HI was 89.3. The group of grade II hydronephrotic kidneys
had an average HI of 83.9. Kidneys with
grade III hydronephrosis averaged 73.0 for HI. Average HI for grade IV
hydronephrotic kidneys was 54.6.The objectivity and reproducibility
of HI measurements have been shown previously [6].


## 4. Discussion

Management of prenatal and infant
HN relies heavily upon serial examination by US [7]. Currently, the main paradigm of HN
description is the SFU grading system. The HI has been shown as a viable,
alternate method of longitudinal HN monitoring [6]. It is an objective,
reproducible, and standardized calculation. Because HI is quantitative and
dimensionless, it allows easy portability of US interpretation across multiple
locations and over time. The medical application of dimensionless numbers has
been shown to be effective [8].As one would expect, kidneys with
more significant HN on average had a lower HI. While the difference in HI between lower grades of HN was minor, mean
HI is markedly different at higher grades (III & IV) of HN. This end of the
spectrum, differentiating between grades III and IV HN, is where the SFU
grading system lacks clarity and depends heavily on individual interpretation
[3]. The value of HI over the SFU
grading system is the greatest in this regard. The subjective factor of visual
interpretation is removed for one observer over time, as are discrepancies between
multiple observers. In its place, an
objective, quantitative interpretation of HN is produced.Serial measurement of HI may be
more sensitive to subtle changes in hydronephrosis, not discriminated or
perceived by the SFU system. Figures2 and
3 demonstrate obvious changes in HN degree in a kidney with static SFU grade.
This sensitivity also holds true for postoperative monitoring, where the SFU
system may not detect results appropriately [5].Figure 2
SFU grade IV hydronephrosis; Calculated HI 58.5.
The dotted line outlines the renal pelvis [black]  as used in calculating HI.Figure 3
Same kidney 1.5 months later. SFU grade IV hydronephrosis; Calculated HI 27. The dotted line outlines the entire renal area, including renal pelvis [black]     and parenchyma (dark gray). While the SFU grade remained the same, the HI has deteriorated significantly, indicating an actual worsening HN.The quantified HI measurement
serves as a “continuous” variable, in contrast to a discrete grade encompassing
a wide range of pathology. This can affect better informed clinical decision making
for a wide variety of hydronephrotic kidneys with diverse clinical settings.
Accordingly, results of hydronephrosis management may improve as well. For example, earlier correction of UPJ
obstruction has been shown to give better drainage [9]. Also, it is clear that
glomeruli are irreparably damaged prior to any evident loss of GFR [10],
suggesting that waiting longer for loss of function to manifest before
intervening would be less than ideal. Therefore, worsening hydronephrosis
constitutes a relative indication for surgery, and our technique better
discriminates subtle changes in HN.This work reviews the HI of 1207 renal units with HN to facilitate establishment of
context for HI. Clinicians can now calculate and use HI with the confidence
that it provides an objective, quantifiable interpretation for the management
of HN. It correlates well with, and improves upon, the SFU grading system for
HN and is especially valuable in management of high-grade HN.The concept of quantification of HN has been addressed previously. Rodríguez et al.
[4] described a series of 81 patients, in which they calculated renal
parenchymal and pelvic areas, in a manner similar to our own. However, their
technique differs in that they propose a computation to derive a threshold
ratio which predicts the need for a surgery. This work, on the other hand,
emphasizes HI as a more sensitive indicator of HN over time, not necessarily as
a singular criterion for, or prognosticator of, surgery.HI does have its limitations. The data (Table1) shows that a wide HI range
represents each SFU grade. For example, the lowest HI for grade I HN is 42, which is obviously quite
low. One inherent problem in a dataset containing greater than 1200 renal units
is the difficulty in accounting for data entry problems.The standard deviation is calculated for each HI and bolsters the constructed
framework. While there is minimal overlap of HI at lower grades of HN, on a
larger spectrum, and the predicted trend is seen. While it may not be used
reliably to compare different patients with HN, the calculated average HI does
provide a reference point for better informed individual HN management.Also, it is possible that some HI measurements were made with a full bladder. As this
work is extracted from a database, original imaging was unavailable for review.
However, this should have been acknowledged and accounted by the clinician at
the time of HI review.


## 5. Conclusion

HI correlates predictably with the
SFU grading system for HN. Because it provides a quantitative measurement, it
can be used to predict the SFU HN grade. HI can also be employed for
longitudinal monitoring of HN by US, including pre- and postoperative
observation. Because it is a more sensitive indicator of renal parenchymal
status, HI allows for better informed clinical decision making, identifying
changes in HN not discerned by the current SFU system.



---

*Source: 960490-2009-02-25.xml*