VARIATION IN KIDNEY LENGTH DURING THE INTRAVENOUS PYELOGRAM

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.

Renal blood oxygenation level-dependent imaging: contribution of R2 to R2* values

OBJECTIVES

The aim of this study was to assess the impact of oral water and intravenous furosemide challenges on blood oxygenation level-dependent magnetic resonance imaging measurements in the kidney and to examine the contribution of R2 (=1/T2) to changes in R2* (=1/T2*).

MATERIALS AND METHODS

This Health Insurance Portability and Accountability Act-compliant study had institutional review board approval, and written informed consent was obtained from all subjects. Nine healthy volunteers were imaged at 3 T on 2 visits. During each visit, a baseline fasting magnetic resonance acquisition was followed by a diuretic challenge: oral water load for the first visit and furosemide for the second. R2* and R2 values in the renal cortex and medulla were measured using multiple gradient echo and multiple spin echo sequences, respectively, and R2' values were computed as R2' = R2* - R2. Timed urinary output was also measured.

RESULTS

Averaged across all subjects, the R2* response to furosemide was greater than to water and greater in the medulla than the cortex. The mean R2 responses exhibited the same trends but were uniformly smaller than the mean R2* responses. The peak changes in R2* and R2 appeared, on average, 10 to 14 minutes before peak urinary output. The median percentage contribution of R2 to R2* changes was 16% in the medulla after both challenges. In the cortex, the median contribution was 48% after water load and 58% after furosemide challenge.

CONCLUSIONS

The contributions of R2 to R2* changes after water load and furosemide challenge are not negligible, especially in the renal cortex. In routine clinical practice, R2* could be used alone as a rough surrogate for R2' in the medulla. However, in the cortex, both R2 and R2* should be measured to obtain accurate values of R2'.

Sensitivity of USPIO-enhanced R2 imaging to dynamic blood volume changes in the rat kidney

PURPOSE

To determine whether MRI in combination with an intravascular contrast agent is sensitive to pharmacologically induced vasodilation and vasoconstriction in the rat kidney.

MATERIALS AND METHODS

R(2) imaging was performed in 25 Sprague Dawley rats at 3 Tesla in the presence of ferumoxytol, an ultrasmall superparamagnetic iron oxide (USPIO) agent with a long plasma half-life. R(2) changes were measured following manipulation of blood volume by intravenous administration of adenosine, a short-acting vasodilator, or N(G)-nitro-L-arginine methyl ester (L-NAME), a long-acting nitric oxide synthase inhibitor with known vasoconstrictive effects. As a control, R(2) responses to adenosine and L-NAME were also examined in the absence of ferumoxytol.

RESULTS

In the presence of ferumoxytol, adenosine induced a significant increase in R(2), while L-NAME produced a reduction, although the latter was not statistically significant. Control experiments revealed small R(2) changes in the absence of ferumoxytol. An incidental finding was that the cross-sectional area of the kidney also varied dynamically with adenosine and L-NAME.

CONCLUSION

Our results suggest that ferumoxytol-enhanced R(2) imaging is sensitive to adenosine-induced vasodilation. The responses to L-NAME, however, were not statistically significant. The variations in kidney size and the R(2) changes in the absence of ferumoxytol may reflect alterations in the volume of the renal tubules.

Reliability of renal length measurements made with ultrasound compared with measurements from helical CT multiplanar reformat images

OBJECTIVE

The purpose of this article is to determine the reliability of sonographic renal length measurements compared with measurements obtained from helical CT multiplanar reformat images and compared with standard renal growth curves.

MATERIALS AND METHODS

A retrospective review was performed of 76 subjects who underwent both renal ultrasound and abdominal CT within 2 weeks of one another. Renal lengths were measured using oblique coronal reformat images of helically acquired CT data by two observers on two occasions. Intraobserver and interobserver error for these measurements were calculated. Ultrasound renal length measurements were compared with CT measurements. Measurement variation was compared with standard renal growth curves.

RESULTS

The mean (± SD) of the absolute value of interobserver error of CT measurements was 0.9 ± 0.8 mm. Compared with CT, individual ultrasound measurements underestimated renal length by 1.5 ± 5.6 mm on average, with a 95% CI of -12.5 to 9.5 mm. When the maximum of three ultrasound renal length measurements was used, the SD was 4.7 mm, with a 95% CI of -8.2 to 10.1 mm of the reported renal length. This corresponds to greater or less than 3.3 years of normal renal growth.

CONCLUSION

Lack of renal growth can be asserted only when renal length falls below the growth curve, taking into account the corresponding measurement error limits, which we found to be greater or less than 9.3 mm. If the follow-up measurement falls within these limits, one should not infer lack of appropriate renal growth, even if the renal length measurement decreases or remains unchanged for up to 3 years.

Sonographic measurement of renal length in children: does the position of the patient matter?

PURPOSE

This prospective study was designed to determine the effect of patient positioning on sonographic measurements of renal length in children. Materials and methods. Two dedicated pediatric ultrasonographers (observers A and B) measured the sonographic lengths of 48 kidneys in 25 children (two had unilateral renal agenesis). Each observer obtained the two "longest possible" measurements for each kidney with the patient in three positions: supine, contralateral decubitus, and prone. Patients with myelomeningocele, hydronephrosis, and renal cysts were excluded.

RESULTS

Both examiners obtained significantly higher values for renal lengths with the children lying supine (observer A P </= 0.0017; observer B P </= 0.0409) or in contralateral decubitus (observer A P </= 0.0001; observer B P </= 0.0419) than with them lying prone. There was no significant difference between the supine and decubitus measurements. The mean difference between the supine and prone measurements for the observers was 3.0 mm for observer A and 1.8 mm for observer B. The mean difference between the contralateral decubitus and prone measurements was 3.0 mm for observer A and 1.6 mm for observer B.

CONCLUSION

Sonographic measurements of renal length made with the patient lying supine or in contralateral decubitus yield slightly higher values than those made with the patient prone.

Sonographic assessment of renal length in children: a reappraisal

Ultrasonography (US) has largely replaced the intravenous urogram as the first modality for the evaluation of the kidneys in children suspected of having urinary tract abnormalities. Because many renal disorders are associated with changes in the sizes of the kidneys, normative standards for assessing renal size have been developed. These standards rely upon comparison of the renal lengths or calculated volumes or both, with various assessments of overall body size, including body surface area, weight, height, and chronological age. We discuss some of the limitations of US in assessing renal size in children. Practical recommendations are offered for optimizing the measurement and interpretation of sonographic renal sizes in children.

High- and low-osmolar contrast agents in urography: a comparison of the appearances with respect to pyelotubular opacification and renal length

The incidence of pyelotubular opacification and the change in renal length during intravenous urography with iohexol (Omnipaque) was compared with sodium/meglumine diatrizoate (Urografin). Pyelotubular opacification was seen in 14 out of 29 urograms performed with iohexol compared with one out of 28 urograms performed with sodium/meglumine diatrizoate. This increased incidence is statistically significant and has not been previously documented. The increase in renal length following intravenous contrast medium was similar for both iohexol and sodium/meglumine diatrizoate. The significance of these findings with respect to the interpretation of urograms performed with iohexol is discussed.

The effect of intravenous contrast medium on glomerular filtration rate

The changes in glomerular filtration rate (GFR) after intravenous contrast medium have been investigated with three contrast media of differing osmolality (monomer, dimer and non-ionic agent) in antidiuretic dogs with three different basal solute excretion rates. A transient increase in GFR after contrast medium was attributed to the wash-out of medullary creatinine at the onset of diuresis. The subsequent fall in GFR was greatest with the contrast media of higher osmolality and in those dogs without an underlying solute diuresis. With the monomer, the decrease in GFR produced a significant decrease in the amount of contrast medium excreted in the first few minutes after contrast injection. It is suggested that an important factor in the decrease in GFR is the rise in pressure in the renal tubules at the start of a diuresis, before they have had time to dilate. An underlying solute diuresis is considered to protect against the fall in GFR because tubular dilatation has already occurred in response to the basal solute load. The decrease in blood pressure during and after contrast medium injection did not correlate with the fall in GFR.

Changes in sizes and distensibility of the aging kidney

Age-related changes in kidney size and distensibility were examined in 103 patients aged 18 to 89 years without evidence of renal disease or hypertension. Kidney dimensions were measured on radiographs obtained 30 s and 5 min after intravenous injection of contrast agent. Kidney distension was calculated by expressing the difference in area between 30 s and 5 min films as a percentage of the area at 30 s. Distension was not significantly correlated with age but wide variation between individuals may limit the value of measurement of this change in size as a diagnostic test. After middle age, kidney length diminished by approximately 0.5 cm per decade. This reduction implies a loss of kidney weight about double that recorded at necropsy. Post-mortem evidence probably underestimates differences between age groups and age-related diminution in kidney size may be greater than post-mortem evidence suggests.

Assessment of renal parenchymal thickness in normal children

The normal range of variation of the parenchymal thickness in well defined parts of the kidney was determined in children (0 to 15 years). The values were correlated with the distance between the superior surface of L1 and the inferior surface of L3. The ratio between the parenchymal thickness on the right side and the left side was also determined. The results are compiled in two nomograms.

Kidney size compared with vertebral height. Importance of possible variations in normal values

Results are presented showing that the normal values derived in one research centre, for the relationship between kidney length and the heights of the first 3 lumbar vertebrae, are not applicable to children in another one. The girls who are the subject of this investigation are those taking part in the survey on asymptomatic bacteriuria in Newcastle upon Tyne.

A simple ultrasonic method for assessing renal size

The relation between renal length (L) and the distance between the first four lumbar transverse processes, (4TP) as measured by sonography and intravenous urography, has been studied in 20 adults with normal urograms. The ratio of L/4TP (Mean +/- 2.S.D.) was 1.04 +/- 0.22 for sonograms and 1.25 +/- 0.26 for urograms. The possible reasons for these differences are discussed. It is suggested that measurement of the distance between the 4TP is a simple method for estimating expected normal renal size in patients referred for renal ultrasonography.

Kidney size in normal children measured by sonography

Kidney length and depth were measured by sonography in 46 normal children fro 0 to 16 years of age. Sonography was used to obtain kidney measurements without the known magnification caused by factors of chemical and photographic nature seen by urography. The results of our study were used to control the age-adapted equipment for renography in children. There was a good correlation between kidney length and depth and variables like age, weight, height and body surface area. The best values were found in the correlations to body surface area. We could confirm the previous findings by other methods of kidney size measurements in children that there is no significant difference in kidney length between boys and girls. The left kidney is slightly longer than the right one and the kidney centre distance is slightly but significantly larger on the left side. No such difference was present in the distance skin to kidney surface.

Kidney distension during IV urography in normal rats and in rats with artificial unilateral renal artery stenosis

Acute changes in kidney size during IV urography were studied in normal rats and in rats with artificial unilateral renal artery stenosis. In normal rats, IV bolus injection of sodium iothalamate (400 mg I/ml), 1.5 ml/kg body weight, produced an increase in area of the renal silhouette by an average maximum of 12.7% after 60 seconds. In nine out of ten rats which developed hypertension after left sided renal artery clamping, renal distension was either small or absent on the stenosed side, while the contralateral right kidney showed normal distension during IV urography. Two out of three rats, which remained normotensive after renal arterial clamping, showed normal distension of both kidneys. These results confirm earlier observations in man that the acute changes in size of the kidney during IV urography can be used as an aid in the urographic screening of hypertensive patients for significant renal arterial stenosis. In all rats with arterial clamp and hypertension, the stenosed kidney was smaller than its contralateral mate. An index between the size of the non-stenosed and the stenosed kidneys greater than 1.15 was only seen in these particular rats.

Kidney size in infants and children assessed by area measurement

A method for assessment of the kidney size in infants and children is described based on measurement of the renal parenchymal area determined planimetrically, using for reference the height of the column of the upper three lumbar vertebrae or the body weight. The kidney size is expressed in standard deviation in the appropriate nomograms.

Kidney size in children. A method of assessment

A method for assessment of kidney size in pediatric practice is presented. Length of the kidney is correlated to length of the lumbar segment L1 to L3 including the intervertebral spaces comprised by these vertebrae. The result may either be expressed in standard deviations or as a kidney ratio. The method makes comparison with films from previous examinations or other hospitals feasible without access to any other data than those available in the film. The method also serves the purpose of properly assessing the growth of the kidneys.

A simple new formula for relating changes in renal length to changes in renal volume

A simple new formula for relating changes in renal length to changes in renal volume is derived. It is not assumed that the kidney is any given shape, but it is assumed that a kidney does not change its shape when it enlarges. It is shown that the fractional change in renal volume equals three times the fractional change in renal length plus three times the fractional change in renal length squared. Examples of applications of the formula using figures for changes in renal length, published elsewhere in the literature, are given for renal hypertrophy in both childhood and adult life and for volume changes during excretion urography.

Renal compensatory hypertrophy in the adult

Compensatory renal enlargement was assessed in 19 adult patients who either had a nephrectomy (17 cases) or developed a functionless kidney following obstruction (two cases). Hypertrophy of the healthy kidney was assessed by comparing renal size on urography before and after removal or destruction of the diseased kidney. Compensatory renal enlargement was demonstrated in 40 per cent of the patients, including two patients in their sixties. The average increase in length was 3 per cent and the maximum increase in length was 9 per cent. Therefore compensatory enlargement does occur in adult life, but is much less than that occurring in childhood. The presence of a hypertrophied adult kidney over 17 cm in length usually indicates that the contralateral renal disease was present in childhood.

Measuring the kidneys-practical applications using a growth and hypertrophy chart

A graphic and practical method for displaying renal growth utilizes a growth-hypertrophy chart. It is best suited for following renal growth on sequential intravenous urograms in patients with urinary tract infection, reflux and problems in which renal growth reflects the efficacy of therapy. The chart uses established standards for normal kidney length, and rates of growth and hypertrophy, and enables one to tell at a glance whether the renal growth is normal. Pitfalls both in the method of measuring the renal lengths and in the interpretation of the measurements are discussed.

Renal distension in response to water-soluble contrast medium and various diuretics

Measurement of the increase in area of the renal silhouette, as it appears on radiographs following the administration of water-soluble contrast medium and certain diuretics, seems to be useful in the diagnosis of renovascular hypertension. In order to assess the optimal technique for such measurements, washout urography was performed in 32 hypertensive patients in two consecutive examinations so that the distensive effect of etacrynic acid, furosemide and hypertonic mannitol, respectively, were compared with that of urea in the same patients. In spite of their stronger diuretic effect, none of the above-mentioned diuretics caused a greater renal distension than urea, the maximum increase in area of the renal silhouette being about 7 to 20%, average about 11%. Since urea is probably the best siuted diuretic for the washout test, it seems to be the drug of choice for these diagnostic procedures.