Renal Vasculature Path

atherosclerosis

most common renal artery disease

plaque deposited in fatty material of arteries

more common in men

risk factors: age, hypertension, smoking, diabetes

medial fibromuscular dysplasia

second most common cause of renovascular disease

nonatherosclerotic disease affects mid to distal segment of vessel

narrow, buldge, or tear of arteries

more in women

produces “string of beads” appearance

less common renal artery diseases

aortic dissection

renal artery aneurysms

arteritis

normal spectral doppler of aorta

rapid systolic uptake, sharp peak, forward diastolic flow but high resistance

PSV b/w 60-100 cm/s

normal spectral doppler renal artery

rapid systolic uptake, blunted peak, forward diastolic flow, low resitance

PSV b/w 90-120 cm/s

renal artery stenosis

<60% stenosis are from renal artery

disordered flow & narrowing of lumen

increased PSV up to 180 cm/s

pressure remains same

no post-stenotic turbulence

renal artery occlusion

confirmed with doppler, color, & power doppler

absence of flow in main renal artery

low velocity dopplers PSV <10

intrinsic parenchymal dysfunction

parenchymal disease results in impedance to arterial flow

indirect renal hilar evaluations

assessment of arteries in the renal hilum as an indicator of renal artery stenosis using AI (acceleration index) & AT (acceleration time)

pitfalls of indirect assessments

AI & AT may seem normal

accessory renal arteries

stenosis may not always affect hilar waveform

no distinction b/w occlusion & stenosis

renal-aortic ratio (RAR)

PSV value comparison

RAR >3.5 is consistent with >60% stenosis

angle of insonation

angle where doppler is placed

difficult in tortuous or curved renal artery

Renal artery waveform analysis

low resistance

RI < 0.7

early systolic peak (ESP)

AT < .07 s (rapid acceleration to peak)

indications of restenosis after renal stent

focal velocity increases

poststenotic turbulence

dampening of distal waveform

abnormalities of renal veins

thrombus, tumor invasion, venous obstruction, recanulization, compression

renal vein thrombus

features: atrophy, increased parenchymal echogenicity, high velocity in presence of compression

we should also look at IVC

renal artery stenosis

caused by atherosclerotic plaque or fibromuscular dysplasia

significant medical problem associated with hypertension

methods to view it:

indirect- look at interlobar & segmental renal arteries

direct- look at aorta & renal arteries

vascular stenosis

lumen narrowed, poststenotic dilation, turbulence, & other downstream changes

tardus parvus

tardus = slow & parvus = small

low & slow to rise

delay in time to PSv & increase in AI

seen in intrarenal waveforms when RAS is present