The study is performed with a curvilinear probe placed in the left and right midaxillary region along the lower costal margin. To obtain a longitudinal view of the kidneys, the probe marker should point toward the head of the bed (Figure 1). The clinician should then slide the probe until the kidney comes into view just caudal to either the liver on the right or the spleen on the left. It is important to remember that the kidneys are retroperitoneal; as such, the probe should be pointed toward the bed to ensure visualization.
Ureteral or bladder outlet obstruction can lead to unilateral or bilateral renal hydronephrosis, which can present on a spectrum ranging from mild to severe. As fluid appears black on ultrasound, hydronephrosis will appear black in what is normally an echogenic center of the kidney. The higher the degree of hydronephrosis, the larger the area of black; in cases of severe hydronephrosis, there is thinning of the renal parenchyma and most of the kidney is taken up by dilated calyces (Figure 3). If there is uncertainty during evaluation, color Doppler may be employed to differentiate the vascular renal hilum from hydronephrosis (Figure 4).
Ureteral stones are not typically visualized by ultrasound. However, intrarenal stones can be found. These will appear as hyperechoic structures within the central area of the kidney with acoustic shadowing artifact noted underneath them. Additionally, while scanning the bladder, one can sometimes find a stone lodged in the ureteropelvic junction (UPJ). One can also look for “ureteral jets,” seen as periodic flow of urine within the bladder using color/power Doppler (Figure 5).
Dr Meer is an assistant professor and director of emergency ultrasound, department of emergency medicine, Emory University School of Medicine, Atlanta, Georgia. Dr Beck is an assistant professor, department of emergency medicine, Emory University School of Medicine, Atlanta, Georgia. Dr Taylor is an assistant professor and director of postgraduate medical education, department of emergency medicine, Emory University School of Medicine, Atlanta, Georgia.