Kidneys Part 1

UT 302 - Abdomen 1

Where are the kidneys located?

In the retroperitoneum at about T12-L4

Where is the right kidney with respect to the liver and gallbladder?

It is posterior and inferior

T/F: the right kidney is higher than the left kidney by 2-8 cm, due to the liver placement

False

Where is the left kidney with respect to the spleen?

It is inferior and medial

T/F: the kidneys can demonstrate 3-4 cm of excursion when a patient changes from a supine to an erect position

True

Where are the adrenal glands with respect to the kidneys?

They are superior, anterior, and medial

The right kidney is ___ to the left kidney by 2-8 cm, due to the liver placement

inferior

What are the main functions of the kidney?

1. Excretion and filtration of waste

2. Synthesis of erythropoietin (EPO), active form vitamin D (calcitriol), and glucose (from glutamine)

3. Regulation of blood volume and blood pressure

What are some wastes that the kidneys filter?

• Urea

• Drugs

• Creatinine

• Bilirubin

How do the kidneys regulate blood volume?

By conserving or eliminating water

How do the kidneys regulate blood pressure?

By secreting renin, angiotensin, and aldosterone (RAAS system)

The kidneys filter ___ liters of blood each day, removing ___ liters of toxins, wastes and water in the process

200; 2

T/F: vitamin D is not important for bone health

False

What is erythropoietin (EPO) and why is it important?

• Healthy kidneys synthesize EPO

• EPO sends a signal to the body to make more red blood cells

• If kidney function is impaired, they can't make enough EPO

• If there is not enough EPO, the body doesn't know to make enough RBCs

What is the average kidney weight?

130-150 g

What is the average kidney length?

10-14 cm

What is the average kidney width?

5-7 cm

What is the average kidney height (AP)?

3-5 cm

Kidney anatomy/embryology

• Start to develop in the 3^rd week of embryo life

  • Develop from columns of mesoderm

• Nephron development begins at 8 weeks GA

• Kidneys migrate from the pelvis to the abdomen at 6-9 weeks GA

What are the 3 successive intervals of kidney development?

1. Pronephros (forekidney)

2. Mesonephros (midkidney)

3. Metanephros (permanent kidney)

Pronephros (forekidney)

A transitory, non-functioning structure, beginning of 4^th week of gestation

Mesonephros (midkidney)

• Late in the 4^th week of gestation

• This structure provides function while the permanent kidney continues to develop

Metanephros (permanent kidney)

Develops during the 5^th week

What is the functional unit of the kidney and what does it do?

Nephrons are the functional unit of the kidney and they produce urine

Kidneys are reddish brown organs with ___ lateral borders and ___ medial borders

convex; concave

The kidneys are protected and stabilized by 3 outer layers which are …

1. Renal fascia (AKA Gerota’s fascia)

   • Superficial layer

2. Adipose capsule

   • Middle layer

3. Renal capsule

   • Deep layer

How does the renal capsule appear on US?

Appears as a strong continuous linear, echogenic reflector surrounding the renal cortex

Gerota’s fascia is the ___ layer, and it encloses the kidney, capsule, and perinephric fat

superficial

What are the white arrow heads pointing to?

Perinephric fat

What are the red arrows pointing to?

Gerota’s fascia

What are the blue arrows pointing to?

Renal capsule

What is the functional section of the kidney called?

Parenchyma

What is the functional section of the kidney (parenchyma) composed of?

1. Renal Cortex

   • Most nephrons here

2. Renal Medulla

3. Renal Pelvis

Where are most of the nephrons located in the renal parenchyma?

In the renal cortex

What is the anatomy of a nephron?

• Composed of a glomerulus and a tubule

  • Glomerulus filters wastes and excess fluids

  • Tubules modify the waste to form urine

• Cleaned blood returns back to the circulation via a renal vein

The glomerulus and convoluted tubules of the nephron are located in the renal , while the collecting ducts are located in the renal _ pyramids

cortex; medullary

The renal ___ surrounds the sinus

parenchyma

The renal ___ is the site of urine formation, and it contains nephrons

cortex

The renal ___ contains pyramids that pass urine to minor calyces

medulla

What structure separates the medullary pyramids?

Columns of Bertin

1

Column of Bertin

2

Cortex

3

Medullary pyramid

4

Sinus fat

5

Renal pelvis

What does the renal cortex look like on US?

• Normal renal cortex has homogeneous echotexture in adults and children

• It is hypoechoic to the liver, spleen, renal sinus

  • It can still be considered normal if it is isoechoic with liver & spleen

• In neonates, the renal cortex is normally isoechoic or hyperechoic compared to the adjacent liver or spleen

A hyperechoic cortex is ___ and should make the sonographer think renal disease

abnormal

Renal cortex

• Extends from the renal capsule to the base of pyramids

• Extends between renal pyramids forming renal columns (AKA columns of Bertin)

Which kidney is normal and which is abnormal?

• Left: normal

• Right: abnormal (they are hyperechoic)

Renal medulla

• The inner portion of the renal parenchyma

• Consists of cone-shaped renal pyramids (inner reddish brown region)

  • Cones are mostly urine collecting tubes

What does the shape of the pyramids in the renal medulla consist of?

• The base (wider end) faces the renal cortex

• The renal papilla (narrower end) faces the renal hilum

• The pyramids are separated by the columns of Bertin

What do neonate kidneys look like on US?

What does medullary nephrocalcinosis look like on US?

How do renal medullary pyramids appear on US?

• Cone-shaped or heart-shaped

• Hypoechoic compared the cortex

• Larger in children

How does the renal sinus appear on US?

• Intense, compact zone of homogeneous central echoes.

  • Hyperechoic

• The echo intensity is caused primarily by hilar adipose tissue, secondary to blood vessels and the collecting system

What is the renal hilum?

• Indentation near the center of concave medial border of the kidney where the following structures enter and leave:

  • Blood vessels

    • Arteries enter

    • Veins leave

  • Lymphatic vessels (take fluid out of kidney)

  • Ureter (exit)

  • Nerves (PSNS and SNS can regulate)

What does this trans image demonstrate?

Shows the renal artery and vein at the renal hilum

What is the renal pelvis?

• Large cavity formed by calyces

• Flat and funnel-shaped

• Continuous with the ureter leaving the pelvis

• Medial to hilum

What does this image demonstrate?

Mild hydronephrosis

What is number 1? Describe its echogenicity compared to the liver

• Renal cortex

• Hypoechoic to the liver

What is number 2? Describe its echogenicity compared to the renal cortex

• Renal medullary pyramids

• Hypoechoic to the renal cortex

What is number 3? Describe its echogenicity compared to the renal cortex

• Renal sinus

• Hyperechoic to the renal cortex

What is number 4? Describe its echogenicity compared to the renal cortex

• Renal capsule

• Hyperechoic to the renal cortex

Is this the right or left kidney?

Right kidney

Is this the right or left kidney?

Left kidney

Label this trans kidney image

1. R kidney

2. R renal vein

3. Ureter

Label this trans kidney image

1. R kidney

2. R renal vein

3. R renal artery

The renal arteries branch ___ to the SMA at the lateral aspect of the abdominal aorta

inferior

Right renal ___ is typically longer than the left

artery

What is the path of the right renal artery?

It courses transversely across the crus of the diaphragm and posterior to the IVC, RRV, the head of the pancreas, and the inferior portion of the duodenum

Right renal ___ is typically shorter than the left

vein

What is the path of the right renal vein?

It courses anterior to the RRA and enters the right lateral aspect of the IVC at a slightly lower transverse plane than the LRV

What is the path of the LRV?

Courses from the left kidney hilus, passes anterior to the LRA, crosses over the aorta anteriorly and passes posterior to the SMA before entering the medial aspect of the IVC

The renal artery transports ___ blood from the heart and aorta into the kidney

oxygenated

The renal vein transports ___ blood from the kidneys to the IVC and heart

deoxygenated

Blood flow from the renal hilum to the parenchyma and renal columns involves …

the renal artery dividing into segmental arteries, branching, entering the parenchyma and passing through the renal columns (into) interlobular arteries

What is the path of blood flow into the kidney via the renal artery?

1. Renal artery

2. Segmental arteries

3. Interlobar arteries

4. Arcuate arteries

5. Interlobular arteries

6. Afferent arterioles

7. Nephrons (in cortex)

What is the path of blood flow out of the kidney via the renal vein?

1. Nephrons

2. Interlobar veins

3. Arcuate veins

4. Interlobar veins

5. Renal vein

1

Renal artery

2

Segmental artery

3

Interlobar artery

4

Arcuate artery

5

Interlobular artery

6

Efferent arteriole

7 & 8

Interlobular vein

9

Arcuate vein

10

Interlobar vein

11

Renal vein

12

Afferent arteriole

What are the main organs of the urinary system?

• Kidneys

• Ureters

• Urinary bladder

• Urethra

What are the ureters, and what is their function?

• Muscular ducts that connect the kidneys to the bladder

• Transport urine from the kidneys to the bladder

What is the main function of the urinary bladder?

Temporarily store urine

What is the urethra, and what is its main function?

• Exit tube

• Discharge urine from the body

What is hydronephrosis?

• Dilation of the renal collecting system.

• Includes

  • Dilation of the renal pelvis (pelviectasis)

  • Dilation of major & minor calyces (caliectasis)

  • Dilated proximal ureter (hydroureter)

Is the collecting system typically visible on US?

Should not really be visible unless an obstruction is present, though the renal pelvis may be somewhat prominent in certain normal patients

What pathology is present in this image?

Stone in distal ureter

How are the kidneys scanned?

• Patient prepped like an abdomen study, plus a full bladder

• Patient is scanned in supine, LLD, and RLD

• Scan both kidneys

  • Compare the renal parenchyma to the liver (right) and spleen (left)

  • Kidney should appear slightly hypoechoic or isoechoic to these structures

• Take longitudinal images, sweeping through the entire kidney (lateral/mid/medial)

• Take transverse images, sweeping through the entire kidney (superior to inferior)

• Measure the kidney in long and transverse

  • Not included in all protocols

What does this image demonstrate?

How to measure the kidneys in transverse and longitudinal

The shape and contour of a normal kidney appear ____ and have internal lobes

smooth

Is this a normal adult kidney?

No