Ultrasound of the kidney: obstruction and medical diseases

Abstract

Ultrasound has emerged as the primary imaging modality in conditions where either renal obstruction or renal medical disease is suspected on the basis of clinical and laboratory findings. In urinary tract obstruction, pathophysiologic changes affecting the pressure in the collecting system and kidney perfusion are well understood and form the basis for the correct interpretation of real-time US and color Doppler duplex sonography (CDDS). Ultrasound is very sensitive for the detection of collecting system dilatation ("hydronephrosis"); however, obstruction is not synonymous with dilatation, as either obstructive or nonobstructive dilatation may be present. To differentiate these conditions, CDDS with measurement of the resistive index (RI) in the intrarenal arteries is extremely helpful, as obstruction (except in the peracute stage) leads to intrarenal vasoconstriction with a consecutive increase of the RI above the upper limit of 0.7, whereas nonobstructive dilatation does not. Diuretic challenge to the kidney may further enhance these differences in RI between obstruction and dilatation. Based on these findings, the present value of US and CDDS in the assessment of the patient with flank pain or renal colic is suggested, especially with respect to promising results for spiral CT and based on cost analysis. In renal medical disease, distinguishing different pathologic conditions using gray-scale US and CDDS (RI) criteria is still very difficult. Nevertheless, US is the fist-line imaging modality in the patient with renal insufficiency.

Renal Relevant Radiology

“…False-negative findings (obstruction without hydronephrosis) can occur in the following settings: retroperitoneal fibrosis/retroperitoneal tumors (due to the inability of the collecting system to dilate), prerenal states/volume depletion, and early obstruction (too early for dilatation to occur) (37). False-positive results (hydronephrosis without obstruction) may occur in the following settings: pregnancy, vesicoureteral reflux, after relief of obstruction, megacystis-megaureter syndrome, full bladder, urinary tract infection, and brisk diuresis (as in nephrogenic diabetes insipidus) (6,38). Thus, when hydronephrosis is identified, tests to confirm the presence of true obstruction may need to be performed (e.g., diuretic renography, Doppler imaging for ureteral jets [ Figure 11]).…”

Sonography and Contrast Enhancement MDCT in the Evaluation of Complicated Autosomal Dominant Polycystic Kidney Disease

“…The typical Sonography figure is generally bilateral, characterized by kidney size with increased echogenicity, with subverted structure by the presence of multiple cysts and spread to the whole body, of varying sizes, with the renal parenchyma poorly represented. Sonography is higly sensitive and specific in patients > 30 years of age, and it's a non-invasive method, of low cost, easily repeatable and achievable [12]. MDCT is even more accurate than US identifying the ADPKD.…”

Evaluation of Renal Venous Impedance, Pyelocalyectasis and Their Correlation during Pregnancy Using Doppler Ultrasound Examination: A Case Control Study

“…The arterial resistive index (RI) measurements have poor sensitivity and specificity for the simultaneous increase in resistance and reduction in compliance. 6,7 Recently, it has been suggested that the venous impedance index is a more sensitive measure of physiologic changes and it can be useful in the evaluation of renal parenchymal compliance in cases of obstruction. 3 Studies have shown mean venous impedance index on the acutely obstructed side to be lower than the index on the unobstructed side.…”