- Email: [email protected]
NEONATAL MANAGEMENT OF UNILATERAL HYDRONEPHROSIS
URETEROPELVIC JUNCTION OBSTRUCTION
0094-0143/98 $8.00
+
.OO
NEONATAL MANAGEMENT OF UNILATERAL HYDRONEPHROSIS Role for Delayed Intervention Stephen A. Koff, MD
The debate over the correct timing of surgical intervention in the newborn for unilateral hydronephrosis suspected of being caused by ureter0 pelvic junction (UPJ) obstruction has been overstated.1sHydronephrosis should be managed no differently in the newborn than in any other age group; UPJ obstruction should be surgically corrected as soon as the diagnosis is made. Surgery is specifically indicated and necessary for any newborn with hydronephrosis caused by an obstruction. Repair should be performed as soon as possible in an attempt to reverse the effects of obstruction, to protect the young rapidly growing kidney from further parenchymal injury and loss of function, and to maximize its future potential. The indication for surgery must be definitive-proven UPJ obstruction. Surgery should not be performed arbitrarily in the absence of obstruction for pseudo-indications such as the size of the renal pelvis, the degree of impairment of differential renal function, or the fear that the hydronephrosis might lead to obstruction in the future. Surgery should also not be performed if the results of diagnostic tests for assessing obstruction are inconclusive or inaccurate or because the results of newborn pyeloplasty have been so successful. The previously mentioned pseudo-indications for surgery, which are based to a great extent on inaccurate diagnosis and an incom-
plete understanding of the pathophysiology and natural history of perinatal hydronephrosis, have resulted in a large number of infants with nonobstructive hydronephrosis undergoing unnecessary surgery. An effective scientifically guided approach to the evaluation and treatment of hydronephrosis in the newborn results from the critical examination of certain issues. 1. The biological uniqueness of the hydronephrotic newborn kidney 2. The natural history of newborn hydronephrosis without surgical therapy 3. The accuracy of tests which assess obstruction
An analysis of these factors reveals several principles. Unilateral neonatal hydronephrosis is a surprisingly benign disease, with the rate of coexisting obstruction being approximately 15% or less. Nearly all infants with primary unilateral UPJ-type hydronephrosis should be initially managed nonoperatively while an assessment for obstruction is undertaken (the exceptions being infants with a tense renal mass or renal infection). A conscientiously applied diagnostic protocol incorporating serial measure-
From the Section of Pediatric Urology, The Ohio State University Medical Center and Children’s Hospital, Columbus, Ohio
UROLOGIC CLINICS OF NORTH AMERICA VOLUME 25 * NUMBER 2 * MAY 1998
181
182
KOFF
ments of renal function, size, and pelvic dilation will permit a conclusive diagnosis of obstruction to be made or excluded with minimal delay. This approach to treatment can be summarized as: operate only for obstruction, do not operate in its absence. THE UNIQUENESS OF NEWBORN HYDRONEPHROSIS
When UPJ-type hydronephrosis is found in the older child or adult, it frequently is caused by a congenital obstruction that has been present for years or decades. Ipsilateral kidney function is usually reduced but often compensated by hypertrophy in the opposite kidney. Despite successful surgery, fixed contralateral compensatory hypertrophy may keep ipsilateral renal function from returning to normal or even improving significantly, and hydronephrosis fails to improve in as many as 40% of cases. Nearly every aspect of hydronephrosis and obstruction in the fetus and newborn is different from that in the older child or adult. The fetal kidney responds to obstruction differently in comparison with the older kidney, with paradoxical responses (vasodilation instead of vasoconstriction) to certain vasoactive peptides.* The fetal and newborn kidneys and their collecting systems are extremely compliant, and, with or without obstruction, the organs dilate dramatically in response to minor changes in pressure, volume, and reflux. Normally, the newborn kidney displays anatomic and functional immaturity and altered blood flow which may change rapidly with time. There is a significant depression in renal function at birth which improves quickly as the kidney rapidly grows and as changes occur in renal vascular resistance and renal perfusion. Transient obstruction in utero delays the maturation of the kidney2 so that even at full-term, the affected kidney displays a pattern of depressed renal function that ordinarily would characterize the kidney in a premature infant. This low glomerular filtration rate may persist for some time before maturation progresses and function increases to age-appropriate levels. Hydronephrosis in the newborn is unstable. Unlike in the older child or adult, it has the potential for spontaneous improvement or resolution (Fig. l ) . l S This may reflect a transiently obstructive or entirely nonobstructive (reflux) etiology. If the hydronephrosis per-
sists or progresses, the cause may be an obstruction which, if uncorrected, will cause further deterioration in renal function. Unlike in the older child or adult, successful surgery in the newborn typically results in marked improvement or elimination of hydronephrosis and enables depressed renal function to improve significantly or even normalize. Once obstruction is relieved, the growing contralateral kidney will no longer be stimulated to undergo compensatory enlargement. If compensatory changes have already occurred, they may regress or disappear, being eclipsed by accelerated growth of the affected kidney.I2 NATURAL HISTORY OF UNILATERAL UPJ-TYPE HYDRONEPHROSIS IN THE NEWBORN
The author is unaware of any randomized controlled scientific studies that have assessed prospectively which newborns with unilateral, primary, UPJ-type hydronephrosis actually have an obstruction and require surgical treatment and which have nonobstructive dilation. Several reports have described the natural history of the newborn with this condition.’, 3 , 5, 1 3 . 14, l 6 For most newborns (S O Y O ) with relatively preserved differential renal function (>%YO) at the time of diagnosis, hydronephrosis is a relatively benign disease; the hydronephrosis does not progress, renal function does not deteriorate, and subsequent surgery is not required. Most studies have not observed the natural history of hydronephrosis in infants with less than 35% differential renal function; surgical intervention has been performed under the assumption that the reduction in renal function was the result of an obstruction in an attempt to prevent further deterioration. As an alternative to a randomized controlled protocol to evaluate the natural history, the author and his colleagues’, did not operate on any newborn with unilateral UPJtype primary hydronephrosis regardless of the initial level of differential function, the degree of hydronephrosis, or the pattern of diuretic renogram washout curve. Surgery was performed only if there was evidence of obstruction as determined by a deterioration in differential renal function with or without progression of hydronephrosis (excluding the birth effect). Of 104 patients followed up for 5 years, 7 (7%) ultimately required pyeloplasty, and, in these cases, surgery successfully returned the differential renal function to predeterioration levels.
NEONATAL MANAGEMENT OF UNILATERAL HYDRONEPHROSIS
Figure 1. Newborn boy with unilateral hydronephrosis identified in utero. Voiding cystogram is normal. A, Ultrasonogram at 2 weeks shows marked hydronephrosis. B, Renal scan demonstrates 35% function in affected kidney at 1 month. C, Ultrasonogram at 3 months shows improvement. D, Ultrasonogram at 6 months shows complete resolution of hydronephrosis. E, Renal scan demonstrates 50% function in affected kidney at 6 months.
183
184
KOFF
Problems were exaggerated in the accurate diagnosis of obstruction in 16 patients in whom severe hydronephrosis was associated with a differential renal function of less than 40% (range, 7% to 40%; mean, 26%). Only one patient (7%) showed a deterioration in differential function from 38% to 20% and required surgery. Postoperatively, renal function rose to more than 40%. In 15 of 16 kidneys, diuretic renographic washout patterns were initially obstructed and clearly inaccurate, with 11 having a flat curve indicating an infinite half-time response. During follow-up, the slope of the washout curve improved for all kidneys, and, for six, it became nonobstructed. Ultrasonography was equally inaccurate. All kidneys initially had grade 4 hydronephrosis using the Society for Fetal Urology guideline^.^ During follow-up, hydronephrosis disappeared in six kidneys and improved in another six, hydronephrosis worsened in one kidney, ultimately requiring pyeloplasty. Likewise, measurements of contralateral compensatory hypertrophy showed it to be absent in 15 of the 16 kidneys. Despite diagnostic appearances that would unequivocally define obstruction in older children and adults, only one of the 16 severely hydronephrotic newborn kidneys in the author’s series was functionally obstructed, developed progressive hydronephrosis and deterioration of function, and required surgery. Based on these observations on nonoperated newborns with severe hydronephrosis with and without significant functional renal deterioration, it is apparent that an accurate diagnosis of obstruction is problematic when tests traditionally used to define obstruction in older patients are applied to newborns. Because these tests do not reflect the unique behavior of the kidney in the newborn, they are inaccurate and should not be relied upon. The only way to make these tests more accurate in the newborn is to change the criteria used for interpretation.
traying large hydronephrotic newborn kidneys with poor function as being obstructed. DEFINITION OF OBSTRUCTION Although obstruction should be easily definable as a significant restriction to urinary outflow, it is more difficult to define in the newborn because the anatomy and function of the kidney change rapidly. This makes it difficult to assess the significance of any restriction to urinary flow. This is compounded further by the fact that there is no useful biochemical or physiologic marker for unilateral obstruction. The effects of obstruction, namely, the presence of hydronephrosis with or without diminished individual kidney function, are invalid indicators of obstruction, because many hydronephrotic kidneys improve spontaneously over time with an increase in renal function and a decrease in hydronephrosis. Despite this shortcoming, obstruction can be defined clinically by its effect on the kidney over time. The author and his colleagues have proposed that obstruction can be defined as ”any restriction to urinary outflow which if untreated will injure the kidney.”s This definition is useful clinically but requires that tests in the infant be performed serially to look for improvement or deterioration in function and anatomy. Although the previous definition is clinically useful in the newborn, PetersI5has suggested that it may not be sufficiently sensitive. He has proposed that obstruction be defined in this age group as any restriction in urinary drainage that impairs the functional potential of the kidney. Although this definition may be more sensitive, it creates difficulty because it requires that the observer be able to assess the functional potential of the hydronephrotic kidney. This is not currently possible with contemporary diagnostic techniques. DIURETIC RENOGRAPHY
THE ACCURACY OF TESTS WHICH ASSESS OBSTRUCTION IN THE NEWBORN The two most common tests to assess the significance of hydronephrosis are ultrasonography and diuretic renography. However, as noted previously, these tests do not accurately assess whether obstruction is present and therefore tend to be misleading by por-
With or without diuretic stimulation, slow washout of tracer from the newborn kidney is expected and is normal. This delay is caused by the combination of diminished glomerular and tubular function which causes a poor response to the diuretic and a disproportionately large renal pelvis which functions as a sluggish mixing chamber. This delayed response pattern is an inaccurate and invalid indicator of obstruction because it occurs reg-
NEONATAL MANAGEMENT OF UNILATERAL HYDRONEPHROSIS
ularly in nonobstructed kidneys in which, over time, hydronephrosis and renal function will improve and the washout pattern actually convert to normal. The diuretic washout pattern should only be considered valid in the newborn with a hydronephrotic kidney when it shows brisk washout and thereby excludes obstruction. The primary role of diuretic renography in the infant with hydronephrosis should be to measure differential renal function. Individual measurements of differential function are subject to inaccuracy. Serial measurements will minimize this possibility and will help to determine whether renal function is improving or deteriorating. If serial measurements indicate that affected kidney function is improving rapidly and appropriately as expected for age, obstruction does not exist and surgery is not indicated. On the other hand, if sequential measurements indicate that renal function is deteriorating, failing to improve, or not improving as expected, obstruction is most likely present and should be corrected immediately with surgery. To interpret changes in differential renal function correctly in this age group, it must be recognized that some kidneys will have significant depression in function at birth which will rapidly increase after birth. This improvement in function, when associated with rapid growth of the kidney, may be so exaggerated that it may overshoot normal and exceed 50% of total function.I2 Although this may appear to be an artifact? l7 it is, in fact, real and actually reflects an active counterbalance between the two kidneys that exists in this age group.7 This is reassuring confirmation that obstruction is not present. ULTRASONOGRAPHY
Ultrasonography has become the standard method for identifying hydronephrosis in infancy. Whereas the magnitude of pelvic enlargement correlates statistically with the likelihood of obstruction, ultrasonography cannot be used to diagnose obstruction because the degree of pelvic dilation neither specifically indicates the presence or absence of obstruction nor predicts whether the hydronephrosis will improve or worsen. This is especially true in the newborn, in whom hydronephrosis may transiently disappear after birth and fluctuate significantly with time, hydration, and bladder fullness. The only way to use ultrasonography meaning-
185
fully in this age group is to obtain serial measurements. Progressive worsening of hydronephrosis usually indicates an obstruction, whereas improvement in hydronephrosis suggests the opposite. Recently, serial ultrasound measurements have been shown to provide another useful parameter in helping to confirm the presence or absence of obstruction by monitoring changes in the growth rate of the normal kidney opposite the hydronephrosis.", l2 In the infant, the active "cross-talk" and counterbalance between the kidneys and their rapid rate of growth (in comparison with kidneys in older patients) permit changes in function in one kidney to affect the rate of growth observable in the other kidney. This anatomic expression of change in function in the normal kidney can be recorded. When the data are visually compared with the changes in function in the hydronephrotic kidney using a renal growth-function chart, the observed changes in differential renal function can be proved to be valid and will reflect the presence or absence of obstruction. A faster-thannormal growth rate (compensatory hypertrophy) in the contralateral kidney suggests that obstruction is present and associated with the hydronephrosis. Conversely, a slower-thannormal growth rate in the normal contralatera1 kidney (compensatory hypotrophy) suggests that the rapid improvement in function, or even supranormal function, in the hydronephrotic kidney is valid and that obstruction is not present. RECOMMENDED FOLLOW-UP PROTOCOL
Based on the previous analysis, the author's approach to the newborn with unilateral UPJ-type hydronephrosis is aimed at determining whether obstruction exists, followed by the administration of therapy based on simple judicial principles-the kidney is considered "innocent" (unobstructed) until "proven guilty" (obstructed). Each newborn with hydronephrosis is evaluated as soon as possible after birth with ultrasound and diuretic renography.'" These studies serve as a baseline. The earlier they are performed, the more visible rapid increases in function and growth will be. Infants are started on a lowdose regimen of antimicrobials, and the studies are repeated at a time interval determined by the differential function in the hydronephrotic kidney'" as follows:
186
KOFF
>40% = 3 months 30% to 40% = 2 months 20% to 30% = 1 month <20% = 2 weeks
If follow-up renography shows that low differential renal function either improves or remains above 40%, and if follow-up ultrasound (excluding the birth effect) demonstrates that the hydronephrosis is not getting worse and the opposite kidney is not displaying compensatory growth acceleration, there is no evidence for obstruction, and nonoperative follow-up should be continued. However, if serial studies display any evidence of obstruction as determined by a change in renal function, growth, or pelvic volume, surgery is indicated immediately. The results of this protocol have helped to invalidate the traditional concept that most cases of newborn hydronephrosis are caused by obstruction and render groundless the tenet that prompt surgical intervention is required in almost all cases to prevent renal damage. Using the guidelines described in this article, the author and his colleagues have not witnessed any permanent loss of renal function. Fewer than 15% of patients have required surgery; hydronephrosis and renal function have improved or remained near normal in the majority; and, in all cases, any transient decrease in renal function has been recovered postoperatively. Unilateral hydronephrosis is a benign disease in the newborn that can safely and beneficially be observed nonoperatively without placing the kidney or the patient at significant risk. Careful and close observation, the socalled ”delayed approach,” seems to be the most prudent regimen for all newborns with unilateral hydronephrosis, because it allows cognitive analysis rather than surgical impulse to direct the management of this unique biologic entity. Because most kidneys in the newborn ultimately are proven to be nonobstructed and do not require surgery, there seems to be no justification to subject patients to early unnecessary surgical intervention simply because of diagnostic inaccuracy.
References 1. Blachar A, Blachar Y, Livne I‘M, et al: Clinical outcome and follow-up of prenatal hydronephrosis. Pediatr Nephrol 8:3(r35, 1994 2. Chung KH, Chevalier RL: Arrested development of the neonatal kidney following chronic ureteral obstruction. J Urol 155:1139-1144, 1996 3. Chung YK, Chang PY, Lin CJ, et al: Conservative treatment of neonatal hydronephrosis. J Formosan Med Assoc 91:75-80, 1992 4. Fernbach SK, Maizels M, Conway JJ: Ultrasound grading of hydronephrosis: Introduction to the system used by the Society for Fetal Urology. Pediatr Radio1 23:478, 1993 5. Freedman ER, Rickwood AM: Prenatally diagnosed pelviureteric junction obstruction: A benign condition? J Pediatr Surg 29:769-772, 1994 6. Fung LCT, McLorie GA, Khoury AE, et al: Contradictory supranormal nuclear renographic differential renal function: Fact or artifact? J Urol 154667470,1995 7. Groshar D, Issaq E, Nativ 0, et al: Increased renal function in kidneys with ureteropelvic junction obstruction: Fact or artifact? Assessment by quantitative single photon emission computerized tomography of dimercapto-succinic acid uptake by the kidneys. J Urol 155:844-846, 1996 8. Koff SA: Problematic ureteropelvic junction obstruction. J Urol 138:390, 1987 9. Koff SA, Campbell K: Nonoperative management of unilateral neonatal hydronephrosis. J Urol 148:525531, 1992 10. Koff SA, Campbell KD The nonoperative management of unilateral neonatal hydronephrosis: Natural history of poorly functioning kidneys. J Urol 15259>595,1994 11. Koff SA, Peller PA: Diagnostic criteria for assessing obstruction in the newborn with unilateral hydronephrosis using the renal growth-renal function chart. J Urol 154:662466, 1995 12. Koff SA, Peller PA, Young DC,et al: The assessment of obstruction in the newborn with unilateral hydronephrosis by measuring the size of the opposite kidney. J Urol 152596599, 1994 13. Maizels M, Mitchell B, Kass E, et al: Outcome of nonspecific hydronephrosis in the infant: A report from the registry of the Society for Fetal Urology. J Urol 152:2324-2327, 1994 14. Nonomura K, Yamashita T, Kanagawa K, et al: Management and outcome of antenatally diagnosed hydronephrosis. Int J Urol 1:121-128, 1994 15. Peters CA: Urinary tract obstruction in children. J Urol 154:1874-1884, 1995 16. Ransley PG, Dhillon HK, Gordon I, et al: The postnatal management of hydronephrosis diagnosed by prenatal ultrasound. J Urol 144:(part 2):584, 1990 17. Steckler RE, McLorie GA, Jayanthi VR, et al: Contradictory supranormal differential renal function during nuclear renographic investigation of hydroureteronephrosis. J Urol 152:600-603, 1994 18. Tripp BM, Homsy YL: Urological review: Neonatal hydronephrosis-the controversy and the management. Pediatr Nephrol 9:50>509, 1995
Address reprint requests to Stephen A. Koff, MD Chief, Section of Pediatric Urology Children’s Hospital 700 Children’s Drive Columbus, OH 43205-2696
0094-0143/98 $8.00
+
.OO
NEONATAL MANAGEMENT OF UNILATERAL HYDRONEPHROSIS Role for Delayed Intervention Stephen A. Koff, MD
The debate over the correct timing of surgical intervention in the newborn for unilateral hydronephrosis suspected of being caused by ureter0 pelvic junction (UPJ) obstruction has been overstated.1sHydronephrosis should be managed no differently in the newborn than in any other age group; UPJ obstruction should be surgically corrected as soon as the diagnosis is made. Surgery is specifically indicated and necessary for any newborn with hydronephrosis caused by an obstruction. Repair should be performed as soon as possible in an attempt to reverse the effects of obstruction, to protect the young rapidly growing kidney from further parenchymal injury and loss of function, and to maximize its future potential. The indication for surgery must be definitive-proven UPJ obstruction. Surgery should not be performed arbitrarily in the absence of obstruction for pseudo-indications such as the size of the renal pelvis, the degree of impairment of differential renal function, or the fear that the hydronephrosis might lead to obstruction in the future. Surgery should also not be performed if the results of diagnostic tests for assessing obstruction are inconclusive or inaccurate or because the results of newborn pyeloplasty have been so successful. The previously mentioned pseudo-indications for surgery, which are based to a great extent on inaccurate diagnosis and an incom-
plete understanding of the pathophysiology and natural history of perinatal hydronephrosis, have resulted in a large number of infants with nonobstructive hydronephrosis undergoing unnecessary surgery. An effective scientifically guided approach to the evaluation and treatment of hydronephrosis in the newborn results from the critical examination of certain issues. 1. The biological uniqueness of the hydronephrotic newborn kidney 2. The natural history of newborn hydronephrosis without surgical therapy 3. The accuracy of tests which assess obstruction
An analysis of these factors reveals several principles. Unilateral neonatal hydronephrosis is a surprisingly benign disease, with the rate of coexisting obstruction being approximately 15% or less. Nearly all infants with primary unilateral UPJ-type hydronephrosis should be initially managed nonoperatively while an assessment for obstruction is undertaken (the exceptions being infants with a tense renal mass or renal infection). A conscientiously applied diagnostic protocol incorporating serial measure-
From the Section of Pediatric Urology, The Ohio State University Medical Center and Children’s Hospital, Columbus, Ohio
UROLOGIC CLINICS OF NORTH AMERICA VOLUME 25 * NUMBER 2 * MAY 1998
181
182
KOFF
ments of renal function, size, and pelvic dilation will permit a conclusive diagnosis of obstruction to be made or excluded with minimal delay. This approach to treatment can be summarized as: operate only for obstruction, do not operate in its absence. THE UNIQUENESS OF NEWBORN HYDRONEPHROSIS
When UPJ-type hydronephrosis is found in the older child or adult, it frequently is caused by a congenital obstruction that has been present for years or decades. Ipsilateral kidney function is usually reduced but often compensated by hypertrophy in the opposite kidney. Despite successful surgery, fixed contralateral compensatory hypertrophy may keep ipsilateral renal function from returning to normal or even improving significantly, and hydronephrosis fails to improve in as many as 40% of cases. Nearly every aspect of hydronephrosis and obstruction in the fetus and newborn is different from that in the older child or adult. The fetal kidney responds to obstruction differently in comparison with the older kidney, with paradoxical responses (vasodilation instead of vasoconstriction) to certain vasoactive peptides.* The fetal and newborn kidneys and their collecting systems are extremely compliant, and, with or without obstruction, the organs dilate dramatically in response to minor changes in pressure, volume, and reflux. Normally, the newborn kidney displays anatomic and functional immaturity and altered blood flow which may change rapidly with time. There is a significant depression in renal function at birth which improves quickly as the kidney rapidly grows and as changes occur in renal vascular resistance and renal perfusion. Transient obstruction in utero delays the maturation of the kidney2 so that even at full-term, the affected kidney displays a pattern of depressed renal function that ordinarily would characterize the kidney in a premature infant. This low glomerular filtration rate may persist for some time before maturation progresses and function increases to age-appropriate levels. Hydronephrosis in the newborn is unstable. Unlike in the older child or adult, it has the potential for spontaneous improvement or resolution (Fig. l ) . l S This may reflect a transiently obstructive or entirely nonobstructive (reflux) etiology. If the hydronephrosis per-
sists or progresses, the cause may be an obstruction which, if uncorrected, will cause further deterioration in renal function. Unlike in the older child or adult, successful surgery in the newborn typically results in marked improvement or elimination of hydronephrosis and enables depressed renal function to improve significantly or even normalize. Once obstruction is relieved, the growing contralateral kidney will no longer be stimulated to undergo compensatory enlargement. If compensatory changes have already occurred, they may regress or disappear, being eclipsed by accelerated growth of the affected kidney.I2 NATURAL HISTORY OF UNILATERAL UPJ-TYPE HYDRONEPHROSIS IN THE NEWBORN
The author is unaware of any randomized controlled scientific studies that have assessed prospectively which newborns with unilateral, primary, UPJ-type hydronephrosis actually have an obstruction and require surgical treatment and which have nonobstructive dilation. Several reports have described the natural history of the newborn with this condition.’, 3 , 5, 1 3 . 14, l 6 For most newborns (S O Y O ) with relatively preserved differential renal function (>%YO) at the time of diagnosis, hydronephrosis is a relatively benign disease; the hydronephrosis does not progress, renal function does not deteriorate, and subsequent surgery is not required. Most studies have not observed the natural history of hydronephrosis in infants with less than 35% differential renal function; surgical intervention has been performed under the assumption that the reduction in renal function was the result of an obstruction in an attempt to prevent further deterioration. As an alternative to a randomized controlled protocol to evaluate the natural history, the author and his colleagues’, did not operate on any newborn with unilateral UPJtype primary hydronephrosis regardless of the initial level of differential function, the degree of hydronephrosis, or the pattern of diuretic renogram washout curve. Surgery was performed only if there was evidence of obstruction as determined by a deterioration in differential renal function with or without progression of hydronephrosis (excluding the birth effect). Of 104 patients followed up for 5 years, 7 (7%) ultimately required pyeloplasty, and, in these cases, surgery successfully returned the differential renal function to predeterioration levels.
NEONATAL MANAGEMENT OF UNILATERAL HYDRONEPHROSIS
Figure 1. Newborn boy with unilateral hydronephrosis identified in utero. Voiding cystogram is normal. A, Ultrasonogram at 2 weeks shows marked hydronephrosis. B, Renal scan demonstrates 35% function in affected kidney at 1 month. C, Ultrasonogram at 3 months shows improvement. D, Ultrasonogram at 6 months shows complete resolution of hydronephrosis. E, Renal scan demonstrates 50% function in affected kidney at 6 months.
183
184
KOFF
Problems were exaggerated in the accurate diagnosis of obstruction in 16 patients in whom severe hydronephrosis was associated with a differential renal function of less than 40% (range, 7% to 40%; mean, 26%). Only one patient (7%) showed a deterioration in differential function from 38% to 20% and required surgery. Postoperatively, renal function rose to more than 40%. In 15 of 16 kidneys, diuretic renographic washout patterns were initially obstructed and clearly inaccurate, with 11 having a flat curve indicating an infinite half-time response. During follow-up, the slope of the washout curve improved for all kidneys, and, for six, it became nonobstructed. Ultrasonography was equally inaccurate. All kidneys initially had grade 4 hydronephrosis using the Society for Fetal Urology guideline^.^ During follow-up, hydronephrosis disappeared in six kidneys and improved in another six, hydronephrosis worsened in one kidney, ultimately requiring pyeloplasty. Likewise, measurements of contralateral compensatory hypertrophy showed it to be absent in 15 of the 16 kidneys. Despite diagnostic appearances that would unequivocally define obstruction in older children and adults, only one of the 16 severely hydronephrotic newborn kidneys in the author’s series was functionally obstructed, developed progressive hydronephrosis and deterioration of function, and required surgery. Based on these observations on nonoperated newborns with severe hydronephrosis with and without significant functional renal deterioration, it is apparent that an accurate diagnosis of obstruction is problematic when tests traditionally used to define obstruction in older patients are applied to newborns. Because these tests do not reflect the unique behavior of the kidney in the newborn, they are inaccurate and should not be relied upon. The only way to make these tests more accurate in the newborn is to change the criteria used for interpretation.
traying large hydronephrotic newborn kidneys with poor function as being obstructed. DEFINITION OF OBSTRUCTION Although obstruction should be easily definable as a significant restriction to urinary outflow, it is more difficult to define in the newborn because the anatomy and function of the kidney change rapidly. This makes it difficult to assess the significance of any restriction to urinary flow. This is compounded further by the fact that there is no useful biochemical or physiologic marker for unilateral obstruction. The effects of obstruction, namely, the presence of hydronephrosis with or without diminished individual kidney function, are invalid indicators of obstruction, because many hydronephrotic kidneys improve spontaneously over time with an increase in renal function and a decrease in hydronephrosis. Despite this shortcoming, obstruction can be defined clinically by its effect on the kidney over time. The author and his colleagues have proposed that obstruction can be defined as ”any restriction to urinary outflow which if untreated will injure the kidney.”s This definition is useful clinically but requires that tests in the infant be performed serially to look for improvement or deterioration in function and anatomy. Although the previous definition is clinically useful in the newborn, PetersI5has suggested that it may not be sufficiently sensitive. He has proposed that obstruction be defined in this age group as any restriction in urinary drainage that impairs the functional potential of the kidney. Although this definition may be more sensitive, it creates difficulty because it requires that the observer be able to assess the functional potential of the hydronephrotic kidney. This is not currently possible with contemporary diagnostic techniques. DIURETIC RENOGRAPHY
THE ACCURACY OF TESTS WHICH ASSESS OBSTRUCTION IN THE NEWBORN The two most common tests to assess the significance of hydronephrosis are ultrasonography and diuretic renography. However, as noted previously, these tests do not accurately assess whether obstruction is present and therefore tend to be misleading by por-
With or without diuretic stimulation, slow washout of tracer from the newborn kidney is expected and is normal. This delay is caused by the combination of diminished glomerular and tubular function which causes a poor response to the diuretic and a disproportionately large renal pelvis which functions as a sluggish mixing chamber. This delayed response pattern is an inaccurate and invalid indicator of obstruction because it occurs reg-
NEONATAL MANAGEMENT OF UNILATERAL HYDRONEPHROSIS
ularly in nonobstructed kidneys in which, over time, hydronephrosis and renal function will improve and the washout pattern actually convert to normal. The diuretic washout pattern should only be considered valid in the newborn with a hydronephrotic kidney when it shows brisk washout and thereby excludes obstruction. The primary role of diuretic renography in the infant with hydronephrosis should be to measure differential renal function. Individual measurements of differential function are subject to inaccuracy. Serial measurements will minimize this possibility and will help to determine whether renal function is improving or deteriorating. If serial measurements indicate that affected kidney function is improving rapidly and appropriately as expected for age, obstruction does not exist and surgery is not indicated. On the other hand, if sequential measurements indicate that renal function is deteriorating, failing to improve, or not improving as expected, obstruction is most likely present and should be corrected immediately with surgery. To interpret changes in differential renal function correctly in this age group, it must be recognized that some kidneys will have significant depression in function at birth which will rapidly increase after birth. This improvement in function, when associated with rapid growth of the kidney, may be so exaggerated that it may overshoot normal and exceed 50% of total function.I2 Although this may appear to be an artifact? l7 it is, in fact, real and actually reflects an active counterbalance between the two kidneys that exists in this age group.7 This is reassuring confirmation that obstruction is not present. ULTRASONOGRAPHY
Ultrasonography has become the standard method for identifying hydronephrosis in infancy. Whereas the magnitude of pelvic enlargement correlates statistically with the likelihood of obstruction, ultrasonography cannot be used to diagnose obstruction because the degree of pelvic dilation neither specifically indicates the presence or absence of obstruction nor predicts whether the hydronephrosis will improve or worsen. This is especially true in the newborn, in whom hydronephrosis may transiently disappear after birth and fluctuate significantly with time, hydration, and bladder fullness. The only way to use ultrasonography meaning-
185
fully in this age group is to obtain serial measurements. Progressive worsening of hydronephrosis usually indicates an obstruction, whereas improvement in hydronephrosis suggests the opposite. Recently, serial ultrasound measurements have been shown to provide another useful parameter in helping to confirm the presence or absence of obstruction by monitoring changes in the growth rate of the normal kidney opposite the hydronephrosis.", l2 In the infant, the active "cross-talk" and counterbalance between the kidneys and their rapid rate of growth (in comparison with kidneys in older patients) permit changes in function in one kidney to affect the rate of growth observable in the other kidney. This anatomic expression of change in function in the normal kidney can be recorded. When the data are visually compared with the changes in function in the hydronephrotic kidney using a renal growth-function chart, the observed changes in differential renal function can be proved to be valid and will reflect the presence or absence of obstruction. A faster-thannormal growth rate (compensatory hypertrophy) in the contralateral kidney suggests that obstruction is present and associated with the hydronephrosis. Conversely, a slower-thannormal growth rate in the normal contralatera1 kidney (compensatory hypotrophy) suggests that the rapid improvement in function, or even supranormal function, in the hydronephrotic kidney is valid and that obstruction is not present. RECOMMENDED FOLLOW-UP PROTOCOL
Based on the previous analysis, the author's approach to the newborn with unilateral UPJ-type hydronephrosis is aimed at determining whether obstruction exists, followed by the administration of therapy based on simple judicial principles-the kidney is considered "innocent" (unobstructed) until "proven guilty" (obstructed). Each newborn with hydronephrosis is evaluated as soon as possible after birth with ultrasound and diuretic renography.'" These studies serve as a baseline. The earlier they are performed, the more visible rapid increases in function and growth will be. Infants are started on a lowdose regimen of antimicrobials, and the studies are repeated at a time interval determined by the differential function in the hydronephrotic kidney'" as follows:
186
KOFF
>40% = 3 months 30% to 40% = 2 months 20% to 30% = 1 month <20% = 2 weeks
If follow-up renography shows that low differential renal function either improves or remains above 40%, and if follow-up ultrasound (excluding the birth effect) demonstrates that the hydronephrosis is not getting worse and the opposite kidney is not displaying compensatory growth acceleration, there is no evidence for obstruction, and nonoperative follow-up should be continued. However, if serial studies display any evidence of obstruction as determined by a change in renal function, growth, or pelvic volume, surgery is indicated immediately. The results of this protocol have helped to invalidate the traditional concept that most cases of newborn hydronephrosis are caused by obstruction and render groundless the tenet that prompt surgical intervention is required in almost all cases to prevent renal damage. Using the guidelines described in this article, the author and his colleagues have not witnessed any permanent loss of renal function. Fewer than 15% of patients have required surgery; hydronephrosis and renal function have improved or remained near normal in the majority; and, in all cases, any transient decrease in renal function has been recovered postoperatively. Unilateral hydronephrosis is a benign disease in the newborn that can safely and beneficially be observed nonoperatively without placing the kidney or the patient at significant risk. Careful and close observation, the socalled ”delayed approach,” seems to be the most prudent regimen for all newborns with unilateral hydronephrosis, because it allows cognitive analysis rather than surgical impulse to direct the management of this unique biologic entity. Because most kidneys in the newborn ultimately are proven to be nonobstructed and do not require surgery, there seems to be no justification to subject patients to early unnecessary surgical intervention simply because of diagnostic inaccuracy.
References 1. Blachar A, Blachar Y, Livne I‘M, et al: Clinical outcome and follow-up of prenatal hydronephrosis. Pediatr Nephrol 8:3(r35, 1994 2. Chung KH, Chevalier RL: Arrested development of the neonatal kidney following chronic ureteral obstruction. J Urol 155:1139-1144, 1996 3. Chung YK, Chang PY, Lin CJ, et al: Conservative treatment of neonatal hydronephrosis. J Formosan Med Assoc 91:75-80, 1992 4. Fernbach SK, Maizels M, Conway JJ: Ultrasound grading of hydronephrosis: Introduction to the system used by the Society for Fetal Urology. Pediatr Radio1 23:478, 1993 5. Freedman ER, Rickwood AM: Prenatally diagnosed pelviureteric junction obstruction: A benign condition? J Pediatr Surg 29:769-772, 1994 6. Fung LCT, McLorie GA, Khoury AE, et al: Contradictory supranormal nuclear renographic differential renal function: Fact or artifact? J Urol 154667470,1995 7. Groshar D, Issaq E, Nativ 0, et al: Increased renal function in kidneys with ureteropelvic junction obstruction: Fact or artifact? Assessment by quantitative single photon emission computerized tomography of dimercapto-succinic acid uptake by the kidneys. J Urol 155:844-846, 1996 8. Koff SA: Problematic ureteropelvic junction obstruction. J Urol 138:390, 1987 9. Koff SA, Campbell K: Nonoperative management of unilateral neonatal hydronephrosis. J Urol 148:525531, 1992 10. Koff SA, Campbell KD The nonoperative management of unilateral neonatal hydronephrosis: Natural history of poorly functioning kidneys. J Urol 15259>595,1994 11. Koff SA, Peller PA: Diagnostic criteria for assessing obstruction in the newborn with unilateral hydronephrosis using the renal growth-renal function chart. J Urol 154:662466, 1995 12. Koff SA, Peller PA, Young DC,et al: The assessment of obstruction in the newborn with unilateral hydronephrosis by measuring the size of the opposite kidney. J Urol 152596599, 1994 13. Maizels M, Mitchell B, Kass E, et al: Outcome of nonspecific hydronephrosis in the infant: A report from the registry of the Society for Fetal Urology. J Urol 152:2324-2327, 1994 14. Nonomura K, Yamashita T, Kanagawa K, et al: Management and outcome of antenatally diagnosed hydronephrosis. Int J Urol 1:121-128, 1994 15. Peters CA: Urinary tract obstruction in children. J Urol 154:1874-1884, 1995 16. Ransley PG, Dhillon HK, Gordon I, et al: The postnatal management of hydronephrosis diagnosed by prenatal ultrasound. J Urol 144:(part 2):584, 1990 17. Steckler RE, McLorie GA, Jayanthi VR, et al: Contradictory supranormal differential renal function during nuclear renographic investigation of hydroureteronephrosis. J Urol 152:600-603, 1994 18. Tripp BM, Homsy YL: Urological review: Neonatal hydronephrosis-the controversy and the management. Pediatr Nephrol 9:50>509, 1995
Address reprint requests to Stephen A. Koff, MD Chief, Section of Pediatric Urology Children’s Hospital 700 Children’s Drive Columbus, OH 43205-2696