Hydronephrosis with diffuse or segmental cortical thinning: Impact on renal function

(1)

HYDRONEPHROSIS WITH DIFFUSE OR SEGMENTAL CORTICAL THINNING: IMPACT ON RENAL FUNCTION

H. SIBAI, J. L. PIPPI SALLE, A. M. HOULE AND R. LAMBERT

From the Divisions of Urology and Nuclear Medicine, The Montreal Children’s Hospital and Hoˆpital Sainte Justine, Montreal, Quebec, Canada

ABSTRACT

Purpose: Management of hydronephrosis has changed considerably with the routine use of prenatal ultrasonography. Increased dependence is now placed on nuclear renographic differential renal function, and many urologists consider surgical intervention for ureteropelvic junction obstruction with significant decrease in renal function (less than 40%). Correlation between differential renal function and the degree of dilatation diagnosed by ultrasound has not been reported. In addition, no difference between hydronephrosis associated with either diffuse or segmental cortical thinning has been made, as both are classified as grade IV according to the Society of Fetal Urology classification. Based on clinical observation we hypothesized that hydronephrotic grade IV kidneys with diffuse parenchymal thinning are associated with worse renal function and are distinct from those with segmental cortical thinning.

Materials and Methods: We performed a retrospective study of patients who underwent pyeloplasty between January 1996 and December 1998. Hydronephrosis was graded according to Society for Fetal Urology classification and all diuretic renograms were performed in a standardized fashion. Grade IV kidneys were divided into IVA (segmental cortical thinning) and IVB (diffuse cortical thinning). Statistical correlation of grade and differential renal function was performed using a chi-square test.

Results: Images were available for review in 77 patients. Average patient age at intervention was 20.4 months and 7.6 years of the prenatally and postnatally detected hydronephrosis groups, respectively. Of the 77 cases 25 had grade IVA and 18 had grade IVB hydronephrosis. Of the grade IVB hydronephrosis cases 66% had less than 40% differential renal function compared to 24% in group IVA (p⬍0.05).

Conclusions: Patients with grade IVB hydronephrosis secondary to ureteropelvic junction obstruction have a higher risk of significant decrease in renal function. Group IVA has significantly better function than group IVB and characteristics similar to grade III hydronephrosis cases. Grade IVB hydronephrosis should monitorized closely as earlier intervention may be warranted to avoid progressive deterioration of renal function.

KEYWORDS: hydronephrosis, kidney, abnormalities Management of hydronephrosis has changed considerably

with the routine use of prenatal ultrasonography. Increased dependence is now placed on nuclear renographic differential renal function, and many urologists consider surgical intervention for hydronephrotic kidneys with significant decrease in renal function (less than 40%) or progressive dilatation.^{1, 2} To our knowledge correlation between differential renal function and the degree of dilatation diagnosed by ultrasound has not been reported. In addition, no difference between hydronephrosis associated with either diffuse or segmental cortical thinning has been made, as both are classified as grade IV according to the Society of Fetal Urology classification.³ Based on clinical observation we hypothesized that hydronephrotic grade IV kidneys with diffuse parenchymal thinning are associated with worse renal function and are distinct from those with segmental cortical thinning.

METHODS

We performed a retrospective study of consecutive patients who underwent pyeloplasty between January 1996 and De- cember 1998. Indications for pyeloplasty were differential renal function less than 40% on the affected side, delayed excretion of radionuclide tracer, progressive dilatation on serial ultrasound and greater than 10% decrease in differen-

tial renal function on serial renography. All ultrasound films were blinded reviewed by 1 investigator who was unaware of the renal function of the affected kidneys.

Hydronephrosis was graded according to Society for Fetal Urology classification with additional subdivision of grade IV hydronephrosis. Grade IV hydronephrosis was classified into IVA (segmental cortical thinning, part Aof figure) and IVB (diffuse cortical thinning, partBof figure). All patients underwent a diuretic renogram using either diethylenetetramine- pentaacetic acid or mercaptoacetyltriglycine-3, which was performed after age 2 months and in a standardized fashion (well- tempered renogram).⁴ The latest ultrasound images and diuretic renogram, performed immediately before pyeloplasty, were used for evaluation. Statistical correlation of grade of hydronephrosis and differential renal function was performed using a chi-square test.

RESULTS

Complete evaluation, including ultrasound films and renograms, was available for review in 77 children. A higher incidence of ureteropelvic junction obstruction was observed in males (2.8:1) and on the left side (1.5:1). Diagnosis was made prenatally in 41 patients and postnatally in 36, and characteristics of hydronephrosis are presented in table 1.

0022-5347/01/1656-2293/0

THEJOURNAL OFUROLOGY^® Vol. 165, 2293–2295, June 2001

2293

(2)

Average patient age at intervention was 20.4 months and 7.6 years of the prenatally and postnatally diagnosed groups, respectively. Mean followup was 17.2 months (range 6 months to 3 years). Of the 77 cases 25 had grade IVA and 18 had grade IVB hydronephrosis. Of the 18 patients with grade IVB hydronephrosis 12 (66%) had less than 40% differential renal function, which was significantly different than group IVA, in which only 6 of 25 (24%) patients had less than 40%

differential renal function (p⫽0.014). Group IVA had characteristics similar to group III hydronephrosis (table 2). Fur- ther analysis of clinical presentation revealed that patients with prenatal diagnosis seemed to have more preserved renal function, although the numbers were not statistically significant (table 3).

DISCUSSION

Our data indicate that children with hydronephrosis and diffuse cortical thinning (IVB) have a significant decrease in differential renal function compared to a hydronephrotic kidney with segmental parenchymal loss (IVA). Further analysis of these data revealed that such significant loss occurred in prenatally and postnatally diagnosed groups. Therefore, ultrasound images provide useful prognostic information for subsequent management.

Other authors attempted to correlate echographic findings and hydronephrotic kidney function. Nitzsche et al analyzed 142 hydronephrotic kidneys and found that less than 10%

had less than 40% function, and all of them had cortical atrophy.⁵Garcia-Pen˜ a et al tried to elaborate a multivariate ultrasound scoring system for obstructive hydronephrosis.⁶ However, their definition of obstruction was based on the washout curve of the diuretic renogram, which is not consid-

ered a reliable parameter to define obstruction.⁷ Cost et al proposed a system to calculate the total renal parenchymal area, making correlations with differential renal function measured by renal scans.⁸ This was a valuable study as it attempted to correlate morphological studies with functional tests. However, the calculation of renal parenchymal area is complex, especially when there is irregular dilatation of the collecting system. Recently, a subsequent study at the same institution using similar methodology indicated that children with diminished total parenchymal area (parenchymal-to- pelvic area of less than 1.6 cm on initial ultrasound) usually require pyeloplasty.⁹ Koff et al also made an interesting observation and noted that contralateral renal hypertrophy is associated with progressive deterioration of function in the hydronephrotic kidney, suggesting that this finding could be used to improve diagnostic accuracy of obstruction.^{10, 11}How- ever these are controversial aspects that have not been val- idated by Brandell et al who analyzed ultrasound images of the contralateral kidneys in children with unilateral hydronephrosis.¹²These authors report an overall decreased mean differential renal function in the group with moderate and severe hydronephrosis but did not mention if there was correlation between differential renal function and hydronephrosis grade.

We previously reported that overall differential renal function is significantly better in prenatally diagnosed patients with ureteropelvic junction obstruction, and recovery of lost renal function is minimal after pyeloplasty.¹³ Therefore, grade IVB hydronephrosis should monitored closely as earlier intervention may be warranted to avoid progressive deterioration of renal function. We realize that the present study has the limitation of being retrospective and segmental areas of preserved parenchyma could be missed on a kidney with diffuse cortical thinning. Also, it would be interesting to perform this study on the entire population of patients with hydronephrosis, including those who improve spontaneously without the need for surgical intervention. Such a study would provide more valuable prognostic information regard- ing the evolution of such cases.

Hydronephrosis with segmental cortical thinning (A) and diffuse cortical thinning (B).

TABLE 1. Hydronephrosis grade

No. Prenatal No. Postnatal Total No.

II 2 3 5

III 14 15 29

IVA 15 10 25

IVB 10 8 18

Totals 41 36 77

TABLE 2. Hydronephrosis grade versus renal function Grade No. Function Less

Than 40% (%)

No. Function 40%

or Greater (%)

II 1 (20) 4 (80)

III 6 (20.6) 23 (79.4)

IVA 6 (24) 19 (76)

IVB 12 (66.6)* 6 (33.4)

* p⫽0.014.

TABLE 3. Clinical presentation versus differential renal function No. Pts. No. 40% or

Greater (%)

No. Less Than 40% (%) Prenatal:

IVA 15 12 (80) 3 (20)

IVB 10 4 (40) 6 (60)

Postnatal:

IVA 10 7 (70) 3 (30)

IVB 8 2 (25) 6 (75)

HYDRONEPHROSIS WITH CORTICAL THINNING

2294

(3)

CONCLUSIONS

Patients with grade IVB hydronephrosis secondary to ureteropelvic junction obstruction have a higher risk of significant decrease in renal function. Group IVA has significantly better function than group IVB and characteristics similar to grade III hydronephrosis. Renal function should be monitored closely in grade IVB hydronephrosis cases as earlier intervention may be required.

REFERENCES

1. Homsy, Y. L. and Koff, S. A.: Problems in the diagnosis of obstruction in the neonate. In: Urologic Surgery in Neonates and Young Infants. Edited by L. R. King. Philadelphia: W. B.

Saunders Co., chapt. 5, pp. 77–94, 1988

2. Park, J. M. and Bloom, D. A.: The pathophysiology of UPJ obstruction: current concepts. Urol Clin North Am,25:161, 1998

3. Fernbach, S. K., Maizels, M. and Conway, J. J.: Ultrasound grading of hydronephrosis: introduction to systems used by the Society for Fetal Urology. Pediatr Radiol,23:478, 1993 4. Conway, J. J.: “Well-tempered” diuresis renography: its histori-

cal development, physiological and technical pitfalls, and standardized technique protocol. Semin Nucl Med,22:74, 1992 5. Nitzsche, E. U., Zimmerhackl, L. B., Hawkins, R. A. et al: Cor-

relation of ultrasound and renal scintigraphy in children with unilateral hydronephrosis in primary workup. Pediatr Neph-

rol,7:138, 1993

6. Garcia-Pen˜ a, B. M., Keller, M. S., Schwartz, D. S. et al: The ultrasonographic differentiation of obstructive versus nonob- structive hydronephrosis in children: a multivariate scoring system. J Urol,158:560, 1997

7. Koff, S. A.: Postnatal management of antenatal hydronephrosis using an observational approach. Urology,55:609, 2000 8. Cost, G. A., Merguerian, P. A., Cherrasarn, S. P. et al: Sono-

graphic renal parenchymal and pelvicaliceal areas: new quan- titative parameters for renal sonographic followup. J Urol, 156:725, 1996

9. Rodrı´gues, L. V., Lock, J., Kennedy, W. A. et al: Evaluation of sonographic renal parenchymal area in the management of hydronephrosis. J Urol,165:548, 2001

10. Koff, S. A., Peller, P. A., Young, D. C. et al: The assessment of obstruction in the newborn with unilateral hydronephrosis by measuring the size of the opposite kidney. J Urol, part 2,152:

596, 1994

11. Koff, S. A. and Peller, P. A.: Diagnostic criteria for assessing obstruction in the newborn with unilateral hydronephrosis using the renal growth-renal function chart. J Urol,154:662, 1995

12. Brandell, R. A., Brock, J. W., III, Hamilton, B. D. et al: Unilat- eral hydronephrosis in infants: are measurements of contralateral renal length useful? J Urol,156:188, 1996 13. Capolicchio, G., Leonard, M. P., Wong, C. et al: Prenatal diag-

nosis of hydronephrosis: impact on renal function and its recovery after pyeloplasty. J Urol,162:1029, 1999

HYDRONEPHROSIS WITH CORTICAL THINNING 2295