The highest yield for US is in patients with risk factors for urinary obstruction, such as pelvic tumors, bladder disorders, prostate hypertrophy, stone disease, and pelvic surgery. In patients without risk factors for obstruction, <1% of patients had US-detected obstruction [4]. Hydronephrosis does not necessarily indicate obstruction; a distended bladder, reflux, pregnancy, postobstructive dilation, or diuresis may cause ureteral and collecting system dilatation. A distended bladder should be decompressed, and the patient should be revaluated. False-negative US studies may be secondary to suboptimal quality, dehydration, early obstruction, or compression of the renal pelvis or ureters by tumors or fibrosis. A secondary role of US is the evaluation of renal size, echogenicity, and morphology to differentiate AKI from CKD and allow determination of prognosis. Normal renal length is >10 cm in the third decade, but renal length correlates with height, sex, age (negative correlation), and weight in normal patients and varies with the state of hydration or presence of an obstruction [3]. Renal size/volume correlates with creatinine clearance [30]. Both kidney size and parenchymal thickness decrease in CKD [31]. Therefore, a normal kidney size suggests AKI rather than CKD. However, infiltrative and inflammatory diseases, as well as renal vein thrombosis, may increase kidney size Renal Failure and parenchymal thickness in AKI or CKD. Increased renal echogenicity is associated with acute and chronic medical renal disease, but this is nonspecific and does not correlate well with renal function. Patients with AKI have only a 30% to 40% chance of increased echogenicity [4,28]. Alternatively, small echogenic kidneys are diagnostic of CKD. Color Doppler is routinely used to assess global perfusion and confirm arterial and venous patency. Color Doppler will differentiate a dilated pelvis from prominent renal veins in the renal sinus and can confirm presence or absence of ureteral jets in the bladder.
Renal Failure. The highest yield for US is in patients with risk factors for urinary obstruction, such as pelvic tumors, bladder disorders, prostate hypertrophy, stone disease, and pelvic surgery. In patients without risk factors for obstruction, <1% of patients had US-detected obstruction [4]. Hydronephrosis does not necessarily indicate obstruction; a distended bladder, reflux, pregnancy, postobstructive dilation, or diuresis may cause ureteral and collecting system dilatation. A distended bladder should be decompressed, and the patient should be revaluated. False-negative US studies may be secondary to suboptimal quality, dehydration, early obstruction, or compression of the renal pelvis or ureters by tumors or fibrosis. A secondary role of US is the evaluation of renal size, echogenicity, and morphology to differentiate AKI from CKD and allow determination of prognosis. Normal renal length is >10 cm in the third decade, but renal length correlates with height, sex, age (negative correlation), and weight in normal patients and varies with the state of hydration or presence of an obstruction [3]. Renal size/volume correlates with creatinine clearance [30]. Both kidney size and parenchymal thickness decrease in CKD [31]. Therefore, a normal kidney size suggests AKI rather than CKD. However, infiltrative and inflammatory diseases, as well as renal vein thrombosis, may increase kidney size Renal Failure and parenchymal thickness in AKI or CKD. Increased renal echogenicity is associated with acute and chronic medical renal disease, but this is nonspecific and does not correlate well with renal function. Patients with AKI have only a 30% to 40% chance of increased echogenicity [4,28]. Alternatively, small echogenic kidneys are diagnostic of CKD. Color Doppler is routinely used to assess global perfusion and confirm arterial and venous patency. Color Doppler will differentiate a dilated pelvis from prominent renal veins in the renal sinus and can confirm presence or absence of ureteral jets in the bladder.