Boris Ajdinović
University of Belgrade, Serbia
Title: Technetium-99m-dimercaptosuccinic acid renal scintigraphy in antenatal hydronephrosis
Biography
Biography: Boris Ajdinović
Abstract
The widespread ultrasound (US) screening during pregnancy has resulted in increasing recognition of antenatal hydronephrosis (ANH). Depending on the diagnostic criteria and gestation, the prevalence of antenatally detected ANH ranges from 0.6% to 5.4%.
The causes of ANH vary from transient benign conditions-transit hydronephrosis, (resolves by birth or during infancy) to conditions that can significantly affect renal function. The outcome of ANH depends on the underlying etiology, so it is very important to determine these causes.
The definition and grading of ANH is based on anteroposterior pelvic diameter (APD) of the fetal renal pelvis. It is an objective parameter, although it varies with gestation, maternal hydration and bladder distension.
ANH is present if the APD is ≥4mm in the second trimester and ≥7mm in the third trimester. ANH is further graded as mild, moderate and severe depending on the size of the measured APD. While fetuses with minimal pelvic dilatation (5-9mm) have low risk of postnatal pathology, the APD ≥15mm at any gestation represents severe hydronephrosis and requires close follow-up.
The examination methods currently used cannot identify obstruction, but only reflect the consequences (decreased renal function, compromised drainage or increased pelvic dilatation). The only useful definition of obstruction is retrospective, defined as “any restriction to urinary outflow that left untreated will damage the kidney,” or defined as “a condition of impaired urinary drainage that if uncorrected will limit the ultimate functional potential of a developing kidney”. Diuretic renography is a cornerstone method for guiding the clinical management of asymptomatic congenital hydronephrosis.
Technetium 99m-dimercaptosuccinic acid renal scintigraphy (99mTc-DMSA) has been used in renal imaging to estimate the functional renal mass (damage the kidney) and relative renal function, especially in pediatric patients. The radiation dose for 99mTc-DMSA scintigraphy has been estimated as 1mSv, regardless of the child’s age.
Under physiological conditions, low molecular weight (LMW) proteins are excreted in the urine by glomerular filtration and then reabsorbed by proximal tubular epithelial cells through a process that is mediated by multi-ligand endocytic receptors: megalin and cubilin. The molecular size of secreted 99mTc-DMSA in the urine is 24-28kDa, which is well within the range of the LMW proteins. These findings suggest that 99mTc-DMSA is handled by kidneys in the same manner as LMW proteins-i.e. it is filtered in glomeruli and subsequently reabsorbed by proximal tubules via megalin-and cubilin-mediated endocytosis. Renal uptake depends on the binding of 99mTc-DMSA to the plasma protein a1-microglobulin, followed by glomerular filtration and megalin/cubilin-mediated endocytosis by proximal tubular cells. Thus, the 99mTc-DMSA scintigraphy is a potential method for the evaluation of proximal tubule endocytic function in patients.
The purpose of this study was to evaluate damage of the kidney with technetium-99m- dimercaptosuccinic acid (99mTc-DMSA) scintigraphy in children with congenital hydronephrosis (CH) and the influence of other postnatal associated diagnoses on abnormal 99mTc-DMSA findings.
Subjects and Methods
99mTc-DMSA scintigraphy in 54 children (17 girls and 37 boys), aged from 2 months to 5 years (median 11 months) with 66 congenital hydronephrotic renal units (RU) (42 unilateral hydronephrosis-29 boys and 13 girls; 12 bilateral hydronephrosis-8 boys and 4 girls) was performed. Male/female ratio was 2,2: 1, unilateral/bilateral hydronephrosis ratio was 4:1. Hydronephrosis classified into three groups according to ultrasound measurement of the antero-posterior pelvic diameter APD): mild (APD 5-9.9mm) was present in 13/66RU, moderate (APD 10-14.9mm) in 25/66RU, and severe (APD ≥15mm) in 28/66RU. Simple hydronephrosis was present in 15RU, and the postnatal associated clinical diagnosis were vesicoureteric reflux (VUR) in 21, pelviureteric junction (PUJ) obstruction in 7, pyelon et ureter duplex in 11, megaureter in 11 and posterior urethra valves in 1RU, respectively. Static renal scintigraphy was performed 2 to 3 hours after intravenous (iv) injection of 99mTc-DMSA using a dose of 50μCi/kg (1.85MBq/kg; minimal dose: 300μCi). Four views (posterior, left and right posterior oblique and anterior) were obtained with a head gamma camera “Orbiter” filtered with high resolution parallel whole collimator. All images were stored in an Pegasys computer with a matrix size of 256×256. The relative kidney uptake (RKU) between the left and right kidney was calculated as an average number counts from anterior and posterior view. Renal pathology was defined as inhomogenous or focal/multifocal uptake defects of radiopharmaceutical in hydronephrotic kidney or as split renal uptake of <40%, and poor kidney function was defined as split renal uptake <10%. Descriptive and analytical statistics (SPSS version 20.0) was performed. Analytical statistics implied the non-parametric Mann-Whitney test for determination of statistically significant difference between the normal and pathological findings on 99mTc-DMS scan. The default level of significance was P<0.05.
Results
Our 99mTc-DMSA scintigraphy findings in children with ANH were: decreased or enlarged kidney with inhomogeneous kidney uptake radiopharmaceutical in 22, irregular shape kidney with inhomogeneous accumulation of radiopharmaceutical in 3, connected (fused) kidney in 1 patient, and poorly or nonvisual kidney in 14RU respectively (total 40/66RU with pathological 99mTc-DMSA finding, 60,6%). Relative accumulation in hydronephrotic kidney was less or equal to 40% in 17RU, less than 10% in 14RU and inhomogeneous radiopharmaceutical uptake with relative accumulation over 40% was detected in 9RU. Regular kidney morphology with homogeneous accumulation of radiopharmaceutical (normal DMSA scintigraphy finding) were found in 26/66RU (39,4%). Statistically significant correlation between the degree of the hydronephrosis (APD) and 99mTc-DMSA scan findings (P<0.001) and between the degree of the VUR and DMSA scan finding (P=0.002) was established. In our study, other associated diagnosis were not statistically correlated with pathological findings on 99mTc-DMSA scan due to low number of patients.
Discussion
Afshin, Safaei et al. found that hydronephrosis was caused by PUJ obstruction in 44.5%, VUR in 22.2%, ureterovesical junction obstruction in 8.9%, posterior urethral valves in 8.9%, PUJ obstruction with VUR in 4.4% and non-VUR non-obstructive in 2.2%. In our study in 22,7%RU (15/66) simple hydronephrosis was present, and VUR in 31.8% (21/66), megaureter in 16,7%, pyelon et uretr duplex in 16,7% (11/66), PUJ stenosis in 10,6% (7/66) and posterior urethral valve in 1,5% (1/66 RU) were detected as an associated diagnosis. Small number in PUJ stenosis in our series is relatively unespected finding. They had (male:female ratio 1.8:1), and unilateral and bilateral hydronephrosis were seen in 73% and 27% of the cases, respectively. This finding is similar to our results (M:F ratio: 2.2:1; bilateral:unilateral ratio: 4:1) .
We demonstrated statistically significant correlation between degree of the hydronephrosis (APD) and 99mTc-DMSA scan finding (P<0.001).
Lee RS et al. and Passerotti CC. et al. found that in children with a history of prenatal dilation of the urinary tract, the incidence of reflux ranges from 12% to 38%. In our group of patients VUR vas present in 31,8% what is in concordance with literature data.
VUR is the only uropathy in which the degree of dilatation of the urinary tract observed on the prenatal and postnatal US does not correlate with increasing risk of pathology. Moreover, there is poor correlation between VUR grade and severity of dilatation.
In our study VUR is the most common associated finding and is diagnosed on MCUG in 21/66RU (31,8%). In 19/21RU (90%) in whom on MCUG VUR was detected, DMSA renal scans was abnormal. Statistically significant correlation between the degree of the VUR and DMSA scan finding (P=0.002) was established.
Other associated diagnosis-megaureter and duplex system was not statistically significantly associated with finding on DMSA scan.
We had only 7/66RU with pyelo-ureteric junction (PUJ) obstruction and we did not have statistically significant correlation between stenosis PUJ and pathological findings on DMSA scan.
Conclusion
Although CH is mostly benign condition and has favorable outcome, it can also cause a significant morbidity. Renal parenchymal damage, estimated by 99mTc-DMSA scintigraphy, is s common finding in children with CH and is in statistically significant correlation with the degree of hydronephrosis. Renal parenchymal damage is common finding in children with CH and VUR and is in statistically significant correlation with the degree of VUR.
On the basis of these results (60% pathological findings) we recommend 99mTc-DMSA scintigraphy in the evaluation renal pathology in children with congenital hydronephrosis. Greater number of patients is needed for the estimation of the associated diagnosis (other than VUR) influence on the renal parenchymal damage in children with CH.