The right kidney is readily demonstrated through the right lobe of the liver. Generally a subcostal approach displays the (more anterior) lower pole to best effect, while an intercostal approach is best for demonstrating the upper pole (Fig. below). The left kidney is not usually demonstrable sagittally because it lies posterior to the stomach and splenic flexure. The spleen can be used as an acoustic window to the upper pole by scanning coronally, from the patient’s left side, with the patient supine or decubitus (left side raised), but, unless the spleen is enlarged, the lower pole must usually be imaged from the left side posteriorly.
ultrasound images of Sagittal section through the normal right kidney (RK), using the liver as an acoustic window. The central echoes from the renal sinus are hyperechoic due to the fat content. The hypoechoic, triangular, medullary pyramids are demonstrated in a regular arrangement around the sinus. The cortex is of similar echogenicity to the liver.
Ultrasound images of TS through the hilum of the RK, demonstrating the renal vein (arrow) draining into the inferior vena cava (IVC) (arrowhead).
Ultrasound images of Left kidney (LK) in coronal section. The renal hilum is seen furthest from the transducer (s = spleen). (Compare this with the sagittal section of the RK in which cortex is seen all the way around the pelvicalyceal system.)
Ultrasound images of The renal cortex lies between the capsule and the lateral margin of the medullary pyramid (arrowheads). Coronal sections of both kidneys are particularly useful as they display the renal pelvicalyceal system (PCS) and its relationship to the renal hilum (Fig. below). This section demonstrates the main blood vessels and ureter (if dilated).
Ultrasound images of Coronal section through the RK demonstrating fetal lobulations (arrows). The pelvicalyceal system (PCS) is mildly distended due to a full bladder. As with any other organ, the kidneys must be examined in both longitudinal and transverse (axial) planes. This usually requires a combination of subcostal and intercostal scanning with anterior, posterior and lateral approaches. The operator must be flexible in approach to obtain the necessary results. The bladder should be filled and examined to complete the renal tract scan. An excessively full bladder may cause mild dilatation of the PCS, which will return to normal following micturition.
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