|Vascular supply from end-to-side|
Usually parallel to incision with hilum inferiorly and posteriorly, extra-peritoneal location. Obtain longitudinal and transverse measurements. Usually hypertrophies ~ 15% in first 2 weeks and may increase by 40% in first 6 months.
Post- operative hematomas- appearance depends upon chronicity. Urine leaks or urinomas- due to anastomotic leaks or ureteric ischemia. Appear well defined, anechoic with occasional hydronephrosis. May use radionuclide imaging to confirm nature of collection. Lymphoceles- occur 4 – 8 weeks after surgery in 15%. May obstruct ureter or veins. Appear well defined and either anechoic or with fine septations.
Screen and image with color/power, looking for focal and/or diffuse hypoperfusion. Obtain spectral traces of interlobar arteries in upper, mid and lower poles with appropriate factors. Image and obtain spectral Doppler of main renal artery and vein and EIA and EIV.
Hyperacute- rarely imaged since it occurs during surgery. Acute- occurs in up to 40% in first few weeks and is a poor long term prognostic indicator. Similar US and radionuclide findings. US findings non-specific.
Obstruction is rare, though will usually be at UV junction from stricture or intra-luminal lesion. Mild pelvocaliectasis may be 2º overhydration, decreased ureteric tone, U-V reflux.
Renal artery thrombosis
Occurs in < 1% typically within first month. Most common cause is acute rejection with retrograde thrombosis of small to large arteries. Other causes: pediatric kidneys, emboli, acquired stenosis, hypotension, vascular kink, hypercoagulable state, poor anastomosis, trauma. US: Absent arterial and venous flow in kidney and main renal artery.
Most common vascular complication in up to 10% in first year. Three possible sites:
– Donor portion, typically at end-to-side anastomosis
– Recipient portion- more uncommon, from intraoperative clamp or intrinsic atherosclerosis
– At anastomosis- more frequent in end-to-end anastomoses
US Findings of RAS
Parvus-tardus flow in intra-parenchymal vessels. Use color Doppler to locate stenosis. Peak systolic velocities > 200 cm/sec with turbulent flow. False positive diagnoses may occur with abrupt turn in the main renal artery. With chronic rejection, segmental renal artery stenoses may occur.
AVM and PSA
Both are typically the result of trauma during percutaneous biopsy. AVM- color shows focal area of mixed colors occasionally with feeding vessels. AVM produces vibrations which result in color assigned to the perivascular tissues.
PSA- may appear as a simple cyst on grey scale imaging but with typical swirling arterial flow on Doppler.
Grey Scale- normal or hypoechoic. Color Doppler- aliasing at stenotic site. Spectral Doppler- 3 to 4 times increase in velocity across the region indicates a hemodynamically significant stenosis.
- Renovascular HT occures in younger patients (less than 30 y.o.)
- Usually respond well to ACE inhibitors
- Renal artery stenosis does not automatically lead to renovascular HT
- >180 cm/s is considered a sign for significant stenosis
- 2:1 is the ratio of increased blood flow bw stenotic and non stenotic segment of the renal artery that is considered to be significant
- RI difference of >10% between the kidneys is an indirect sign for stenosis
- RI is decreased in the post stenotic arterial segments (decreased blood flow -> decreased vascular resistance)
- ACC (Acceleration time) increases in stenotic segments