Renal Ultrasound: Sonography of the Kidneys

Review literature: (Singer et al, 2006).

Technique of Renal Ultrasound

Sonography of the kidney is best done in supine position and with inspiration of the patient. In adverse conditions, an elevation of the examination side by 30 degrees is helpful.

Each kidney is scanned in longitudinal section and cross section. The upper pole is located more dorsally than the lower pole, the transducer must be tilted to the dorsum. Transducers use either sector or curved-array technology with 3.5 to 5 MHz.

Normal Renal Ultrasound Findings

Size if the Kidney

Length: 100–115 mm
Width: 50–70 mm
Depth: 30–50 mm

The size of the parenchyma is measured from the convex outer edge to the tip of a papilla, the normal value is 13–18 mm. The kidney volume of 110–200 ml and can be calculated by using the following formula:

kidney volume

length × width × depth × 0.5

Renal parenchyma pyelon index:

The relationship between the dorsal parenchyma to pyelon to ventral parenchyma is normally 1:1:1. With increasing age, the kidney atrophy shifts the renal parenchyma pyelon index to 1:2:1.

Renal Ultrasound Anatomy

The kidney is a bean-shaped organ, which has usually a smooth convex lateral organ boundary. The renal parenchyma is homogeneously hypoechoic, sometimes the medullary pyramids are somewhat less echogenic than the cortex. The surrounding fat tissue and the pyelocaliceal system with parapelvic fat is hyperechoic. Medial to the pyelocaliceal system, sections of the great vessels are visible.

The urogenital organs, especially the kidneys, have a broad range of anatomical variations, which cause confusion in ultrasound imaging. Tumor-like lesions have to be clarified with computed tomography (CT), often they are harmless [fig. renal pseudotumor].

renal ultrasound of a pseudotumor of the kidney

Ultrasound of a renal pseudotumor: CT-imaging revealed a buckling of the renal parenchyma.

Doppler-Sonography of the Renal Vessels

Indications for renal Doppler sonography:

Suspected renal artery stenosis or renal hypertension
Suspected renal infarction
Assessment of renal function after transplantation

Standard flow rates of the renal artery:

Peak systolic velocity (PSV): 80–150 cm/s
End-diastolic velocity (EDV): 20–50 cm/s

Resistive index of the kidney

The resistive index (RI) is calculated with the peak systolic velocity (PSV or V_PSV) and the end-diastolic velocity (EDV or V_EDV) using following formula:

Formula Resistive Index

The location for the assessment of PSV and EDV are the arcuate arteries or interlobar arteries at the border between cortex and medulla. The standard value for the resistive index is 0.5 to 0.7. A RI of >0.7 or a side difference of more than 0.1 are seen in hydronephrosis, renal transplant graft rejection or intrinsic renal disease. An RI of less than 0.5 is a sign for a renal artery stenosis.

24-hour urine

Index

Examinations

Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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References

Singer u.a. 2006 SINGER, Eric A. ; GOLIJANIN, Dragan J. ; DAVIS, Robert S. ; DOGRA, Vikram:: What’s new in urologic ultrasound?
In: Urol Clin North Am
33 (2006), Aug, Nr. 3, S. 279–286

Deutsche Version: Sonographie der Nieren

Last update:

Dr. med. Dirk Manski (E-Mail)