The role of ultrasound in renal insufficiency: the essentials

An Objective Computer-Assisted Measurement of Sonographic Renal Cortical Echogenicity: The Splenorenal Index

ABSTRACT

Renal cortical echogenicity represents a marker of renal function. However, evaluation of the renal echotexture is subjective and thus disposed to error and interrater variability. Computer-aided image analysis may be used to objectively assess renal cortical echogenicity by comparing the echogenicity of the left kidney to that of the spleen; the resultant ratio is referred to as the splenorenal index (SRI). We performed a retrospective review of all adult patients who received a renal ultrasound over a 45-day period at our institution. Demographic data and kidney function laboratory values were documented for each patient. Regions of interest (ROIs) were selected in the left renal cortex and spleen using ImageJ software. The SRI was calculated as a ratio of the mean pixel brightness of the left kidney cortex ROI to the mean pixel brightness of the spleen ROI. The SRI was then correlated with serum creatinine, blood urea nitrogen, and estimated glomerular filtration rate. We found that among the 94 patients included in the study, the SRI had a significant positive correlation with serum creatinine ( r = 0.43, P < 0.001) and serum blood urea nitrogen ( r = 0.45, P < 0.001) and negative correlation with estimated glomerular filtration rate ( r = -0.47, P < 0.001). Our data indicate that SRI may serve as a valuable tool for sonographic evaluation of renal parenchymal disease.

Machine Learning-Aided Chronic Kidney Disease Diagnosis Based on Ultrasound Imaging Integrated with Computer-Extracted Measurable Features

Although ultrasound plays an important role in the diagnosis of chronic kidney disease (CKD), image interpretation requires extensive training. High operator variability and limited image quality control of ultrasound images have made the application of computer-aided diagnosis (CAD) challenging. This study assessed the effect of integrating computer-extracted measurable features with the convolutional neural network (CNN) on the ultrasound image CAD accuracy of CKD. Ultrasound images from patients who visited Severance Hospital and Gangnam Severance Hospital in South Korea between 2011 and 2018 were used. A Mask regional CNN model was used for organ segmentation and measurable feature extraction. Data on kidney length and kidney-to-liver echogenicity ratio were extracted. The ResNet18 model classified kidney ultrasound images into CKD and non-CKD. Experiments were conducted with and without the input of the measurable feature data. The performance of each model was evaluated using the area under the receiver operating characteristic curve (AUROC). A total of 909 patients (mean age, 51.4 ± 19.3 years; 414 [49.5%] men and 495 [54.5%] women) were included in the study. The average AUROC from the model trained using ultrasound images achieved a level of 0.81. Image training with the integration of automatically extracted kidney length and echogenicity features revealed an improved average AUROC of 0.88. This value further increased to 0.91 when the clinical information of underlying diabetes was also included in the model trained with CNN and measurable features. The automated step-wise machine learning-aided model segmented, measured, and classified the kidney ultrasound images with high performance. The integration of computer-extracted measurable features into the machine learning model may improve CKD classification.

Accuracy of Multi-organ Point-of-Care Ultrasound for Acute Kidney Injury Etiologies

This study investigated the diagnostic performance of point-of-care ultrasound (POCUS) for acute kidney injury (AKI) etiological subgroups in emergency department (ED) patients. Multi-organ POCUS including kidney, bladder, inferior vena cava (IVC), lung and cardiac examinations were used to identify five AKI subgroups: hypovolemia, reduced cardiac output, systemic vasodilatation and renal vasomodulation, renal and post-renal. One hundred sixty-five AKI patients were included in the study. The most diagnostic parameter in the post-renal group was the presence of any hydronephrosis, with a sensitivity of 93.3% (95% confidence interval [CI]: 68.1-99.8) and specificity of 85.9% (95% CI: 79.3-91.1). For the reduced cardiac output group, the most diagnostic parameter was IVC maximum diameter &gt;17 mm with a sensitivity of 100% (95% CI: 83.2-100) and specificity of 70.2% (95% CI: 61.6-77.7). For the hypovolemia group, the most diagnostic parameter was IVC maximum diameter ≤17.9 mm with a sensitivity of 81.2% (95% CI: 71.2-88.8) and specificity of 56.5% (95% CI: 44-68.4). For the systemic vasodilatation and renal vasomodulation group, the most diagnostic parameter was diffuse ascites with a sensitivity of 56.3% (95% CI: 29.9-80.2) and specificity of 89.9% (95% CI: 83.8-94.2). None of the parameters were significant for the renal group. We concluded that multi-organ POCUS is of diagnostic value for AKI subgroups.

Ultrasonographic predictors in chronic kidney disease: A hospital based case control study

BACKGROUND

Prevalence of Chronic Kidney Disease (CKD) is increasing globally with the concomitant upsurge in diabetes mellitus and hypertension. We explored the research question whether Ultrasonographic (US) renal parameters are potential predictors of CKD?

MATERIALS AND METHODS

A case control study was conducted at a tertiary care hospital that included 50 confirmed cases of CKD and 100 nondiseased controls. Renal length, renal parenchymal thickness, and renal cortical thickness were measured in both cases and controls by ultrasound examination. Corticomedullary differentiation and renal cortical echogenicity were also assessed.

RESULTS

US parameters of renal length, renal parenchymal thickness, and renal cortical thickness were found to be significantly and strongly associated with the presence of CKD. The strongest association was observed with renal cortical echogenicity (OR 27.33, 95% CI 8.82-84.63). The association of reduced renal cortical thickness (OR 6.14, 95% CI 1.59-23.62), and renal length (OR 2.72, 95% CI 1.13-8.26) were independent and significant predictors of presence of CKD.

CONCLUSIONS

Specific US parameters of renal cortical echogenicity, cortical thickness, and length of kidney have a strong potential for independently establishing the diagnosis and evaluation of progression of CKD.

Diagnostic performance of renal ultrasonography in detecting chronic kidney disease of various severity

Background

Association between early diagnosis of chronic kidney disease (CKD) and low morbidity and mortality rate has been proven. Thus, tools for early CKD diagnosis are vital. Ultrasonography has been widely used to diagnose and monitor the progression of CKD.

Objectives

To determine the performance of selected renal ultrasonographic parameters for the diagnosis of early CKD.

Methods

In a cohort of patients diagnosed with CKD (n = 100), diagnostic performance of ultrasonographically measured renal length (RL), renal cortical thickness (RCT), and parenchymal thickness (PT) was determined using receiver operating curve analysis; correlation of each parameter with the associated comorbidities and serum creatinine (Scr) levels was also determined. Severity of CKD was graded with estimated glomerular filtration rates (eGFR).

Results

Of all patient participants, 85 had severity grades 2 or 3. Mean (standard deviation) Scr was 1.88 (0.60) mg/dL; eGFR was 43.3 (11.85) mL/min/1.73 m2. RL was 9.01 (0.83) cm, PT was 1.32 (0.22) cm, and RCT was 6.0 (0.10) mm. PT and RCT were positively correlated with eGFR (P = 0.01 and 0.002, respectively). Early CKD was better predicted by PT (area under the curve (AUC) 0.735; 82% sensitivity; 30% specificity; 68% positive predictive value (PPV)) and RCT (AUC 0.741; 82% sensitivity; 48% specificity; 51% PPV); severe CKD was better predicted by RL (AUC 0.809; 67% sensitivity; 26% specificity, 45% PPV; 13% negative predictive value).

Conclusion

Index ultrasonic parameters show a diagnostic role in different stages of CKD. The index ultrasound and biochemical parameters showed a complementary role in predicting renal dysfunction.

Clinical utility of ultrasonographic evaluation in acute kidney injury

Background

This study aimed to evaluate ultrasonography (US) in patients with acute kidney injury (AKI) and the association of US findings with its clinical characteristics.

Methods

This single-center retrospective study evaluated US in AKI patients. A healthy control group was matched by sex and age at a ratio of 2:1 with the AKI group. The US characteristics were compared between the two groups.

Results

The US characteristics of 111 patients with AKI were evaluated. Compared with the control group, AKI patients had greater kidney length and kidney volume (P<0.05). Patients with AKI also displayed thicker parenchyma than those in the control group, but only the difference in the right kidney was found to be significant. Of the 111 AKI patients, 38 had positive US findings including increased parenchymal echogenicity, increased renal resistance index (RRI), and hydronephrosis, while only 5 patients had increased RRI. The cause of AKI was attributed to obstructive nephropathy in eight patients.

Conclusions

Although US evaluation indicated that most of the patients with AKI were “normal ultrasound imaging”, abnormal findings beyond obstructive nephropathy were still detected in some cases. Aside from its ability to exclude obstructive nephropathy, US evaluation might hold further value. It was found that the kidney size of AKI patients is significantly larger than that of healthy controls. Kidney size combined with other ultrasound indicators could hold potential for the evaluation of AKI.

Keywords

Acute kidney injury (AKI); ultrasonography (US); clinical characteristics; parenchymal echogenicity; renal resistance index (RRI)

Noninvasive Monitoring and Evaluation of the Renal Structure and Function in a Mouse Model of Unilateral Ureteral Occlusion Using Microcomputed Tomography

Mouse unilateral ureteral occlusion (UUO) is widely used as a model of renal experimental obstructive nephropathy with interstitial fibrosis. Microcomputed tomography (micro-CT) imaging has the potential to produce quantitative images. The aim of this study was to establish standard images of micro-CT for renal anatomic and functional evaluations in a mouse model of UUO. UUO was induced in adult male mice BALB/c. In total, 27 mice were used in this study. Three mice per group (a total of 6 groups) were examined with contrast-enhanced micro-CT prior to UUO (day 0) and on days 1, 3, 5, 7, 10, and 14 after UUO. In order to determine the histopathologic correlations at each point in time, contrast-enhanced micro-CT imaging was performed in the 18 remaining mice. All animals were sacrificed, and both kidneys were harvested after the final micro-CT examination. UUO resulted in hydronephrosis and changes in the renal parenchyma. The predominant alteration was substantial changes in the hemodynamics of the renal vascular system after ureteral obstruction for 24 hours or longer, which may be resulting from increased action of vasoconstrictors versus vasodilators. The renal parenchyma was significantly reduced after 1 week, and the features of the histologic changes supported the findings of the micro-CT images. In the contralateral unobstructed kidneys, the images showed a normal structure and function and the pathohistology revealed a normal histoarchitecture. Micro-CT is a useful tool for providing noninvasive monitoring and evaluating the renal structure and function.

Ultrasound and color Doppler applications in chronic kidney disease

Chronic kidney disease (CKD) includes all clinical features and complications during the progression of various kidney conditions towards end-stage renal disease (ESRD). These conditions include immune and inflammatory disease such as: primary and hepatitis C virus (HCV)-related glomerulonephritis; infectious disease such as pyelonephritis with or without reflux and tuberculosis; vascular disease such as chronic ischemic nephropathy; hereditary and congenital disease such as polycystic disease and congenital cystic dysplasia; metabolic disease including diabetes and hyperuricemia; and systemic disease (collagen disease, vasculitis, myeloma). During the progression of CKD, ultrasound imaging and color Doppler imaging (US-CDI) can differentiate the etiology of the renal damage in only 50-70% of cases. Indeed, the end-stage kidney appears shrunken, reduced in volume (Ø < 9 cm), unstructured, amorphous, and with acquired cystic degeneration (small and multiple cysts involving the cortex and medulla) or nephrocalcinosis, but there are rare exceptions, such as polycystic kidney disease, diabetic nephropathy, and secondary inflammatory nephropathies. The main difficulties in the differential diagnosis are encountered in multifactorial CKD, which is commonly presented to the nephrologist at stage 4-5, when the kidney is shrunken, unstructured and amorphous. As in acute renal injury and despite the lack of sensitivity, US-CDI is essential for assessing the progression of renal damage and related complications, and for evaluating all conditions that increase the risk of CKD, such as lithiasis, recurrent urinary tract infections, vesicoureteral reflux, polycystic kidney disease and obstructive nephropathy. The timing and frequency of ultrasound scans in CKD patients should be evaluated case by case. In this review, we will consider the morpho-functional features of the kidney in all nephropathies that may lead to progressive CKD.

Should renal color Doppler ultrasonography be a routine test in newly diagnosed hypertensive patient?

: European Society of Hypertension/European Society of Cardiology guidelines recommend calculation of estimated glomerular filtration rate and evaluation of urinary albumin excretion rate as routine tests in the initial evaluation and during the follow-up of all hypertensive patients. However, from a clinical point of view, renal ultrasound - a noninvasive, readily available and cheap imaging modality - could contribute to the better evaluation of a hypertensive patient by identifying common causes of secondary hypertension (HTN) originating from the kidney and more recently by detecting renal injury in severe or long-standing essential HTN by measuring renal resistive indexes. The purpose of this review is to summarize the actual evidence which could support a larger use of renal ultrasound in the work-up of patients with newly diagnosed HTN.

A modified elliptical formula to estimate kidney collagen content in a model of chronic kidney disease

The extent of scarring or renal interstitial collagen deposition in chronic kidney disease (CKD) can only be ascertained by highly invasive, painful and sometimes risky, tissue biopsy. Interestingly, while CKD-related abnormalities in kidney size can often be visualized using ultrasound, not only does the ellipsoid formula used today underestimate true renal size, but the calculated renal size does not inform tubulointerstitial collagen content. We used coronal kidney sections from healthy mice and mice with kidney disease to develop a new formula for estimating renal parenchymal area. While treating the kidney as an ellipse with the major axis (a) the polar distance, this technique involves extending the minor axis (b) into the renal pelvis to obtain a new minor axis, b_e. The calculated renal parenchymal area is remarkably similar to the true or measured area. Biochemically determined kidney collagen content revealed a strong and positive correlation with the calculated renal parenchymal area. Picrosirius red staining for tubulointerstitial collagen also correlated with calculated renal parenchymal area. The extent of renal scarring, i.e. kidney interstitial collagen content, can now be computed by making just two axial measurements which can easily be accomplished via noninvasive imaging of this organ.

Clinical significance of renal cortical thickness in patients with chronic kidney disease

PURPOSE

The aim of this study was to evaluate the correlations between laboratory findings and ultrasonographic measurements of renal length and cortical thickness in patients receiving follow-up for chronic kidney disease (CKD).

METHODS

A total of 41 CKD patients (18 males and 23 females; mean age, 65.2 years; range, 42 to 85 years) with a low glomerular filtration rate who did not require renal replacement therapy were included in this prospective study. Patients were followed up with laboratory assays at bimonthly intervals and with ultrasonography performed twice a year. Renal cortical thickness, renal length, and estimated glomerular filtration rate (eGFR) values were compared using the paired-samples t test. Additionally, Pearson correlation analysis was conducted between renal length and cortical thickness measurements and eGFR values to assess kidney function.

RESULTS

At the beginning of the study and after 24 months, mean eGFR values of the 41 patients were 35.92 mL/min and 28.38 mL/min, respectively. The mean renal length was 91.29 mm at the beginning of the study and 90.24 mm at the end of the study. The mean cortical thickness was 5.76±2.05 mm at the beginning of the study and 5.28±1.99 mm at the end of the study. A statistically significant positive association was found between eGFR and mean renal length (r=0.66, P<0.01) and between eGFR and mean cortical thickness (r=0.85, P<0.01), with the latter being more prominent.

CONCLUSION

Our study suggests that ultrasonographic cortical thickness measurements may be an important imaging technique in the follow-up care of patients with CKD.

Role of ultrasonographic chronic kidney disease score in the assessment of chronic kidney disease

PURPOSE

Ultrasonography (US) is an inexpensive, noninvasive and easy imaging procedure to comment on the kidney disease. Data are limited about the relation between estimated glomerular filtration rate (e-GFR) and all 3 renal US parameters, including kidney length, parenchymal thickness and parenchymal echogenicity, in chronic kidney disease (CKD). In this study, we aimed to investigate the association between e-GFR and ultrasonographic CKD score calculated via these ultrasonographic parameters.

METHODS

One hundred and twenty patients with stage 1-5 CKD were enrolled in this study. The glomerular filtration rate was estimated by the Chronic Kidney Disease Epidemiology Collaboration equation. US was performed by the same radiologist who was blinded to patients' histories and laboratory results. US parameters including kidney length, parenchymal thickness and parenchymal echogenicity were obtained from both kidneys. All 3 parameters were scored for each kidney, separately. The sum of the average scores of these parameters was used to calculate ultrasonographic CKD score.

RESULTS

The mean age of patients was 63.34 ± 14.19 years. Mean kidney length, parenchymal thickness, ultrasonographic CKD score and median parenchymal echogenicity were found as 96.2 ± 12.3, 10.97 ± 2.59 mm, 6.28 ± 2.52 and 1.0 (0-3.5), respectively. e-GFR was positively correlated with kidney length (r = 0.343, p < 0.001), parenchymal thickness (r = 0.37, p < 0.001) and negatively correlated with CKD score (r = -0.587, p < 0.001) and parenchymal echogenicity (r = -0.683, p < 0.001). Receiver operating characteristic curve analysis for distinction of e-GFR lower than 60 mL/min showed that the ultrasonographic CKD score higher than 4.75 was the best parameter with the sensitivity of 81% and positive predictivity of 92% (AUC, 0.829; 95% CI, 0.74-0.92; p < 0.001).

CONCLUSION

We found correlation between e-GFR and ultrasonographic CKD score via using all ultrasonographic parameters. Also, our study showed that ultrasonographic CKD score can be useful for distinction of CKD stage 3-5 from stage 1 and 2. We suggested that the ultrasonographic CKD score provided more objective data in the assessment of CKD.

Effect of Low-Osmolar Intravenous Contrast on Renal Length

OBJECTIVE

The purpose was to study the effect of low-osmolar nonionic contrast on renal length.

MATERIAL AND METHODS

This study included 56 patients (4-phase renal computed tomography [CT] and 4-phase CT urogram [CTU], 19 patients each; split-phase CTU, 18 patients). Three radiologists created the best off-axis plane and renal lengths measured on a postprocessing workstation. Two-way analysis of variance with Bonferroni corrections was performed along with single-sample t tests.

RESULTS

Four-phase renal CT and CTU average differences from unenhanced phases were 0.30/0.16 mm (corticomedullary), 0.88/1.33 mm (nephrographic), and 2.17/2.22 mm (delayed). The nephrographic and delayed phases were significantly different from their unenhanced phase (P < 0.01). Nonsignificant differences between the corticomedullary phase and the unenhanced phase were observed (P = 0.217, 4-phase renal CT; P = 0.232, 4-phase CTU). The split-phase CTU average difference in the enhanced phase was 1.36 mm (P < 0.001).

CONCLUSION

Renal length increases 1 to 2 mm with low-osmolar nonionic contrast.

Correlation of ultrasonographic parameters with serum creatinine in chronic kidney disease

OBJECTIVE

The purpose of our study is to correlate renal echogenicity with serum creatinine in order to determine the significance of renal echogenicity when it comes to identifying the progression of chronic kidney disease (CKD) and for the sonographic grading of CKD.

MATERIALS AND METHODS

Sixty patients above 30 years of age who had been diagnosed with CKD according to the guidelines of the National Kidney Foundation were included in the study. Patients on kidney replacement therapy or with fatty liver findings on ultrasonography were excluded. Ultrasounds of kidneys were performed by two radiologists who were blind to the patients' serum creatinine levels. Renal cortical echogenicity was compared with serum creatinine. Statistical analysis was performed using one-way ANOVA followed by Scheffe's test. The relationship between serum creatinine and sonographic features was assessed by correlation coefficient analysis. A P value less than 0.05 was considered statistically significant.

RESULTS

Mean serum creatinine was 2.80 mg/dl for Grade 1 (range: 0.9-9.2 mg/dl), 3.69 mg/dl for Grade 2 (range: 1.2-10.3 mg/dl), 3.86 mg/dl for Grade 3 (range: 1.1-6.5 mg/dl), and 7.90 mg/dl for Grade 4 (range: 3.1-11.4 mg/dl). The grades being determined by cortical echogenicity on imaging A statistically significant, positive correlation was observed between serum creatinine and grading based on cortical echogenicity (P = 0.004).

CONCLUSION

Renal echogenicity and its grading correlates better with serum creatinine in CKD than other sonographic parameters such as longitudinal size, parenchymal thickness, and cortical thickness. Hence, renal echogenicity is a better parameter than serum creatinine for estimating renal function in CKD, and has the added advantage of irreversibility.

Ultrasound tissue characterization of the normal kidney

AIM

Ultrasound tissue characterization (USTC) is a precursor of ultrasound virtual histology (USVH), already applied to B-mode images of coronary, carotid, and peripheral arteries, as well as venous thrombosis. Elevated echogenicity has been described for a rejected transplanted kidney. We analyzed data from healthy young adults as reference for further renal USTC.

METHODS

Ultrasound kidney images of 10 volunteers were analyzed. Pixel brightness in the 0-to-255 range was rescaled to zero for black and 200 for fascia brightness before automatic classification into 14 ranges, including "blood-like" (0-4), "fat-like" (8-26), "hypoechoic muscle-like" (41-60), "hyperechoic muscle-like" (61-76), 4 ranges of "fiber-like" (112-196), "calcium-like" (211-255) and intermediary intervals. Nomenclature was readapted using nonechoic, hypoechoic I to IV, echoic I to IV, hyperechoic I to IV, and saturated echoes to avoid inference to actual kidney tissue. Descriptive and comparative statistics were based on percentages of pixels in specific brightness ranges.

SAMPLE POPULATION

Eight women and 2 men, 26 ± 4 years (range, 22-34 years) old, were studied. Kidney length was 10.5 ± 0.9 cm (9.0-12.0 cm). Doppler US resistivity index was 0.67 ± 0.03 (0.62-0.71).

RESULTS

Original fascia brightness converted to 200 value had a mean ± SD of 206 ± 16 (range, 181-236). Kidney grayscale median averaged 37 ± 6 (27-48). Most pixels were hypoechoic II to IV (8-60), averaging 78% ± 6% (66%-87%). Percentages for fat-like, intermediary fat/muscle-like, and hypoechoic muscle-like intervals averaged 25%, 28%, and 25%, respectively.

CONCLUSIONS

A reference database for USTC/USVH of normal young kidneys was created for future comparisons with transplanted and abnormal kidneys. Normal renal echoes have low brightness. Hyperechoic pixels may represent abnormalities.

Assessment of renal fibrosis with diffusion-weighted MR imaging: study with murine model of unilateral ureteral obstruction

PURPOSE

To test, in a murine model of unilateral ureteral obstruction (UUO), whether the magnetic resonance (MR) imaging-derived apparent diffusion coefficient (ADC) changes during the progression of renal fibrosis and correlates with the histopathologic changes observed in renal fibrogenesis.

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. A UUO was created in each of 14 mice. In five mice, longitudinal diffusion-weighted (DW) imaging was performed before the UUO (day 0) and on days 3 and 7 after the UUO and was followed by histopathologic analysis. The nine remaining mice were examined with cross-sectional studies on days 0 (n = 4) and 3 (n = 5). ADCs were measured with a spin-echo echo-planar sequence at five b values ranging from 350 to 1200 sec/mm(2). Differences in ADC among the time points and between the sides were assessed by using Tukey-Kramer and Student t tests, respectively. ADC was correlated with cell density and alpha-smooth muscle actin (alpha-SMA, a marker of myofibroblasts) expression at linear regression analysis.

RESULTS

Histopathologic examination revealed typical renal fibrosis on the side with UUO. The ADC decreased over time on the UUO side, from (1.02 +/- 0.06 [standard deviation]) x 10(-3) mm(2)/sec on day 0 to (0.70 +/- 0.08) x 10(-3) mm(2)/sec on day 3 (P < .001) and (0.57 +/- 0.10) x 10(-3) mm(2)/sec on day 7 (P < .001). The percentage change in ADC was greater on the UUO side than on the contralateral side on days 3 (29% +/- 9, P = .05) and 7 (44% +/- 11, P < .01). ADC correlated with both increased cell density and increased alpha-SMA expression (P < .001 for both correlations).

CONCLUSION

An ADC decrease in renal fibrosis is associated with an increased number of cells, including fibroblasts. ADC has the potential to serve as a sensitive noninvasive biomarker of renal fibrosis.

Three-dimensional ultrasonography can detect the modulation of kidney volume in two-kidney, one-clip hypertensive rats

As volume changes are a typical finding in the two-kidney, one-clip hypertensive rat model (2K1C), it is of interest to investigate within what time frame these volume changes occur and their relation to hypertension. Kidney volume changes in Wistar rats were measured by three-dimensional (3D) ultrasonography (USG). Clipped induced stenosis was applied to the left renal artery in 11-wk-old animals (n = 8), using age-matched nonclipped rats as controls (n = 7). Ultrasonographic recordings were made before clipping and, thereafter, weekly with corresponding systolic blood pressure and body weight measurements. The nonclipped kidney showed increased volume at week 2, 5 and 7. Three wk after clipping, clipped kidneys were smaller than the nonclipped kidneys (0.47 +/- 0.11 mL versus 1.28 +/- 0.07 mL). No difference was found between the left and right kidney in the control group at any week. Blood pressure was significantly higher in the 2K1C hypertensive group 4 weeks after clipping (201 +/- 16 versus 139 +/- 4 mm Hg) with stable blood pressure thereafter. Three-dimensional USG showed that clipping caused a decrease in kidney volume from week 3 in the clipped kidney and a volume increase in the nonclipped kidney at week 2. A significant increase in blood pressure appeared after week 4.