Kidneys 2

UT 302 - Abdomen 1

___ hypertension is one of the most common causes of secondary hypertension

Renovascular

What causes renovascular hypertension?

It is mostly due to the narrowing of blood vessels in the kidney

___ affects 75 million adults in the United States and accounts for 8.6% of all primary care visits

Hypertension

Renovascular hypertension is one of the most common causes of ___ hypertension and often leads to resistant hypertension

secondary

What is renovascular hypertension?

Systemic hypertension that manifests secondary to the compromised blood supply to the kidneys, usually due to an occlusive lesion in the main renal artery

Renal artery disease

• Correctable

• Treatment will control or cure renovascular hypertension

• Retention of renal mass

• Stabilization of renal function

Why is duplex ultrasound is used to detect renal artery stenosis?

• Provides anatomical as well as hemodynamic functional information

• Low cost without risk of ionizing radiation or use of nephrotoxic contrast agents

Kidney anatomy

• Retroperitoneal organs

• Located between 12^th thoracic and 3^rd lumbar vertebrae

• Right kidney inferior to left

• Kidney length is 9-13 cm and width is 5-7 cm

  • May decrease in size with age

T/F: Variation in size between a person's two kidneys is not common, and is therefore abnormal

False

The ___ kidney is typically slightly longer or larger than the ___ kidney

left; right

A size difference of up to ___ is considered within normal limits

1-1.5 cm

A variation of ___ or more or one kidney being significantly larger than the other may suggest an abnormality (which should be medically investigated)

2 cm

For sonographic examination, the kidney is divided into what four parts?

1. Renal hilum

2. Renal cortex

3. Renal medulla

4. Renal sinus

What is the renal hilum?

Area through which renal artery, vein, nerves, and ureter enter the kidney

What four structures pass through the renal hilum?

1. Renal artery

2. Renal vein

3. Nerves

4. Ureter

What is the renal sinus?

• Cavity that contains the renal artery and veins and collecting and lymphatic system

• Largely made up of fat and fibrous tissue

• Appears brightly echogenic on sonographic imaging

What two structures compose the renal parenchyma?

1. Medulla

2. Cortex

What is the renal medulla?

• Contains 12–18 renal pyramids (triangular shaped)

  • Carry urine from cortex to renal pelvis

  • Lower echogenicity than cortex

What is the renal cortex?

• Outermost area of kidney

• Lies just beneath renal capsule

• Area in which urine is produced

• Some cortical tissues extends between medullary pyramids (columns of Bertin)

Which kidney has an abnormal echogenicity?

Right image (an adult kidney should not be hyperechoic to the liver)

Label the image

1. Lateral

2. Medial

What is the transpyloric plane?

• Important landmark for identification of kidneys

• Located halfway between suprasternal notch and symphysis pubis

• Cuts through lower border of first lumbar vertebrae, ninth costal cartilage, and pylorus

• Renal arteries identified 2 cm below this plane

1

Renal artery

2

Interlobar arteries

3

Arcuate arteries

4

Interlobular arteries

5

Interlobular veins

6

Arcuate veins

7

Interlobar veins

8

Renal vein

9

Segmental artery

10

Segmental vein

What is a lobe vs. lobule?

• Lobe

  • Large, macroscopic anatomical division of an organ

  • Visible without a microscope

• Lobule

  • Much smaller microscopic subdivision within a lobe

  • Only visible with a microscope

The renal arteries branch off …

anterior, lateral, or posterolateral from the abdominal aorta

Right renal artery

• Longer than LRA

• Travels posterior to the IVC and RRV

Left renal artery

• Branches off aorta more superior (cephalad) than RRA

• Shorter than RRA

What happens to the renal arteries?

1. Branch off aorta and travel to their respective kidneys

2. Enters renal hilum

3. Branches into segmental arteries (ant/post, sup/inf)

4. Branch into interlobar arteries

5. Branch into arcuate arteries

6. Branch into interlobular arteries

1

R renal artery

2

R renal vein

How is the renal artery arranged compared to other vessels when it enters the hilum?

Typically located posterior and inferior to the renal vein in the renal hilum

How is the renal vein arranged compared to other vessels when it enters the hilum

Typically located anterior and superior to the renal artery in the renal hilum

T/F: the renal vein exits the kidney in front of the renal artery, which enters behind the renal pelvis

True

The RRA is the only vessel that travels laterally ___ the IVC

under

Is it possible to have multiple renal arteries on each side?

• There is usually one on either side, though multiples are quite common

• Occur in 14-25% of the population

• There can be duplicate, three or more

The main renal arteries usually enter the kidney at the ___, though accessory vessels may enter at the ___ or other surfaces of the renal parenchyma

hilum; poles

Renal arteries have ___ resistance waveforms

low

Which waveform is low-resistance and which is high-resistance?

• Top: high-resistance

• Bottom: low-resistance

1

Interlobular arteries

2

Arcuate arteries

3

Interlobar artery

4

Segmental artery

Intrarenal arterial anatomy consists of …

• An arbor-like network of vessels coursing throughout the kidney

• Once the renal artery enters the kidney it divides into

  • Segmental arteries (usually 5)

  • Interlobar arteries

  • Arcuate arteries

  • Interlobular arteries

Renal veins course __ in the renal hilum

anterior

The renal artery lies ___ the renal vein and the ureter

between

The right renal vein has a ___ course from the kidney to the IVC

short

The left renal vein courses ___ to the aorta just below the SMA and has a much ___ course than the RRV

anterior; longer

What vessel are the arrows pointing to?

LRV

The left renal vein is ___ and ___ to the renal artery

anterior; superior

What is being shown in this image?

RRV draining into IVC

What are some renal anomalies?

• Horseshoe kidney

• Duplicate renal artery

• RRA superior to IVC

• Bifid LRV

• Retroaortic LRV

Horseshoe kidney

• Kidneys are joined at the lower poles

• Isthmus lies anterior to the aorta at the level of L4-L5

Duplicate renal artery

• Often arises from aorta below main renal artery

• Course to polar surfaces of kidney

What are the most common etiologies of renal arterial disease?

1. Atherosclerosis

2. Fibromuscular dysplasia

Atherosclerosis

• Most common etiology of renal arterial disease

• Lesions affect ostium and proximal 3rd of vessel

• More common in men than women

• Bilateral 30% of the time

• Risk factors include age, hypertension, smoking, diabetes, hyperlipidemia, past history of CAD or PAD

Fibromuscular dysplasia

• Second most common curable cause of renovascular disease

• Nonatherosclerotic disease affects mid-to-distal segment of vessel

• Occurs more commonly in women aged 25–50 years

• Often bilateral

• Produces “string of beads” appearance on ultrasound or angiogram

What are some other (less common) disease processes that can impact renal arteries?

• Aortic dissection

• Aneurysms of main or segmental renal arteries

• Aortic coarctation proximal to renal arteries

• Arteriovenous fistulae

• Arteritis

• Extrinsic compression by tumor or other mass

What do normal renal veins look like on US?

Anechoic lumens and respiratory phasicity on Doppler

What kind of flow occurs in the renal arteries in the presence of thrombosis?

Continuous, nonphasic low-velocity flow

What are some abnormalities of renal veins on US?

• Acute thrombus

• Partial venous obstruction

• Recanalization

• Collateralization

• Extrinsic compression

What settings must be optimized in order to identify renal vein abnormalities?

• B-mode

• Doppler

What does this image demonstrate?

Normal flow in mid renal vein of right kidney

How should patients be prepared for renal US?

• Patients should fast 8–10 hours prior to exam

• Reduces excessive abdominal gas

• Exam is usually scheduled in the morning

• Diabetic patients may be permitted to have dry toast and clear liquids if needed

• Patients should refrain from smoking or chewing gum prior to exam to reduce amount of swallowed air

How should the patients be positioned for renal US?

• Supine with head slightly elevated

  • Reverse Trendelenburg can be used to shift visceral contents into lower abdomen and pelvis

• Right or left lateral decubitus positions used to evaluate kidneys and mid-to-distal renal artery segments

• Prone position also works well to access kidneys

What should be examined during renal US?

• Aorta

• Celiac trunk

• Proximal SMA

• Renal ostia

• Proximal-to-mid renal artery segments

How should the sonographer be positioned to perform a renal US?

• Positioned to side of bed

• Height of bed should be adjusted so that sonographer can scan without overextended arm

• Patient should lie as close to sonographer’s side of bed as possible

• Avoid overreaching

• Sonographer should learn to scan with both hands

How should the kidneys be examined on US?

• High-resolution ultrasound system

  • Phased or curved array 2–5 MHz transducer

  • Gray scale used to localize vessels and organs

    • Identify atherosclerotic plaque, aneurysmal dilation, and dissections

• Color and/or power Doppler may help visualize arteries and veins (landmarks, regions of disordered flow, and vessel occlusion)

• Spectral Doppler used for differentiation of normal and abnormal flow patterns

• Optimization of color and spectral Doppler settings must be performed throughout exam

What are some helpful scanning techniques that are used to scan the renal arteries?

• Access from midline, transverse plane

• Lie inferior to left renal vein

• Keep transducer perpendicular to abdominal wall

• Angle slightly to right or left to create sagittal image of renal artery

• Color flow used to help identify vessels

• Vessels can usually be identified from ostium to mid segment

What are the landmarks in this image?

1. RRA

2. LRA

3. SMA

What does this image demonstrate?

Sagittal color-flow image of the RRA