The document summarizes the technique for performing an ultrasound examination of the kidneys. It outlines the proper probe selection, patient positioning, and scanning approaches. It describes how to obtain longitudinal and transverse views of both kidneys and minimum images that should be included. Normal kidney anatomy is defined including dimensions, cortex thickness and echogenicity compared to liver. Causes of non-pathological renal pelvis dilation are listed.

1. Ultrasound examination of
Kidneys
Dr Swaroop
PGRD

2. Probe selection
• In the adult patient- a curved array transducer
• In the pediatric patient -a linear array transducer
Patient positioning
Patient is usually placed in supine position.
Best position is lateral decubitus
Kidneys are examined in longitudinal and transverse scan planes with the transducer placed in the flanks
Examination technique and positioning
Probe maybe
kept at a oblique
plane
corresponding
to the lie of the
kidney on the
psoas muscle.

3. Slowly tilt/fan the probe anteriorly and posteriorly to assess the entire
kidney
Step 1: RIGHT Kidney Ultrasound Longitudinal View

4. Step 2: RIGHT Kidney Ultrasound Transverse View
Tilt the probe superiorly and inferiorly

5. Scanning apporach
A combination of subcostal and intercostal approaches is required to evaluate the kidneys fully; the upper
pole of the let kidney may be particularly difficult to image without a combination of approaches.
Barriers to scanning
1)Artifacts of the lowest ribs always shadow the upper poles of the kidneys.
 Ask the patient to take a deep breath and hold.
 Ipsilateral arms can be raised to widen rib spaces
2)When insonation of the kidney is obscured by intestinal air
 The supine scan position is combined with the lateral decubitus position and the transducer moved dorsally.
In obese patients
A prone position scanning approach can be used

6. A renal examination series should include the following minimum images;
•Both kidneys with length measurements
•Right kidney longitudinal section with liver for comparison
•Both kidneys longitudinal, anterior and posterior sections
•Both kidneys transverse at level of
• Superior pole
• midpole
• Inferior pole
•Left kidney longitudinal with spleen for comparison
•Document the normal anatomy. Any pathology found in 2 planes, including measurements and any vascularity

7. What to Check
•Kidney size (should not be >1cm difference between sides)
•Cortical thickness(not <10mm)
•Cortico-medullary differentiation
•Cortex at least as hypoechoic as the liver
•Pyramids slightly hypoechoic relative to the cortex
•No hydronephrosis
•Renal scarring(beware mistaking prominant lobulations as scars)

8. Normal adult kidneys
Right vs left kidney
 The Right kidney is slightly smaller than the left kidney
 The left kidney lies 1-2cm higher than the right kidney.
Renal dimensions have the following normal ranges:
Length 9-11 cm
Width 4-7 cm
Thickness 3-5 mm
Renal anatomy
 The kidney is surrounded by a capsule separating the kidney from the echogenic perirenal
fat, which is seen as a thin linear structure
 The kidney is divided into parenchyma and renal sinus.

9. RENAL SINUS
 The renal sinus is hyperechoic and is composed of calyces, the renal pelvis, fat
and the major intrarenal vessels.
 In the normal kidney, the urinary collecting system in the renal sinus is not visible,
but it creates a heteroechoic appearance with the interposed fat and vessels.
The parenchyma is more hypoechoic and homogenous and is divided into
 The outermost cortex
 The innermost and slightly less echogenic medullary pyramids
 Between the pyramids are the cortical infoldings, called columns of Bertini
In the pediatric patient, it is easier to differentiate the hypoechoic medullar pyramids
from the more echogenic peripheral zone of the cortex in the parenchyma rim, as
well as the columns of Bertini
Normal renal cortex is typically less echogenic than adjacent liver and spleen

10. Cortical thickness measurement and echogenicity
 Cortical thickness should be estimated from the base of the pyramid and is
generally 7–10 mm.
 If the pyramids are difficult to differentiate, the parenchymal thickness can be
measured instead and should be 15–20 mm
 The echogenicity of the cortex decreases with age and is less echogenic than or
equal to the liver and spleen at the same depth in individuals older than six
months
 In neonates and children up to six months of age, the cortex is more echogenic
than the liver and spleen when compared at the same depth

11. Non pathological causes of Dilated Renal pelvis
 With increased fluid intake the renal pelvis can distend and be visualized as a more echo free structure.
 A similar finding can be seen in a developmental variant of an extrarenal pelvis.
 In both conditions ,the dilation does not involve the calyces and infundibula

13.  An enlarged adrenal gland should be looked for within the
perirenal fat above the upper pole of the kidney, where it
can appear as a hypoechoic mass within the echogenic
perirenal fat.

16. REFERENCES
• RUMACK
• Ultrasonography of the Kidney: A Pictorial Review-NIH-NLM
• Ultrasound teaching manual