Abdominal sonography
- kidneys are reduced in size or show a lateral difference of > 1.5 cm (Hoyer 2015)
- surface smooth with small retractions
- rarely larger scarring retractions occur
- Parenchyma:
- Parenchymal rim narrow
- Echogenicity normal to increasing
- Parenchymal defects as an indication of past renal embolism or renal infarction
- Due to arteriosclerotic altered renal vessels:
- in the parenchyma and in the hilar region small echoes with attenuation or extinction of sound
- vessels sometimes pulsating and double contoured (Seitz 2008)
Color-coded duplex sonography (FKDS): Color-coded duplex sonography is the best screening method for suspected renal artery stenosis (Herold 2021). Sensitivity is 85% and specificity is 92% (Prischl 2017). Pathological values are:
- intrarenal resistance index (RI) < 0.5
- Lateral difference of the RI > 5
- Vmax A. renalis ≥ 2 m/s.
The result in color-coded duplex sonography depends on the experience of the examiner (Herold 2021). Especially in case of V. a. unilateral processes of the kidney this examination is indispensable (Geiger 2003).
MR angiography: MRI angiography is the second choice in terms of diagnostics. The advantage is that the examination is non-invasive. The disadvantage is an overestimation of the degree of stenosis (Hoyer 2015). The sensitivity is 100% and the specificity is 96% (Prischl 2017). MR angiography is contraindicated from a GFR< 30 ml / min with gadolinium, otherwise there is a risk of nephrogenic systemic fibrosis (Herold 2021).
Spiral CT: Here, a relative contraindication exists with the use of a potentially nephrotoxic contrast agent from a GFR < 30 ml / min. In addition, the radiation exposure is quite high (Herold 2021). The sensitivity of spiral CT is 93% and the specificity is 81% (Prischl 2017).
Intra-arterial digital subtraction angiography (i.a.- DSA): i.a.- DSA is the gold standard for confirming the diagnosis. However, it should only be performed if the patient agrees to possible PTA and the possibility of balloon catheter dilatation exists. On examination, a hemodynamically relevant stenosis can be estimated from a systolic transtenotic pressure gradient of > 10 - 15 % (Herold 2021).
Captopril-assisted renal scintigraphy: It is an established investigation of the functional relevance of a stenosis and is conclusive for renovascular hypertension. A positive test result is positively predictive of improvement in blood pressure after intervention. However, sensitivity decreases with impaired renal function (Oberhuber 2019).
The following tests are no longer recommended as screening tests for ischemic nephropathy:
- selective renal vein renin determination
- Captopril- radionucleide- scintigraphy (sensitivity is > 90 % and specificity > 90 % (Prischl 2017).
- Captopril- test
- Plasma renin activity (sensitivity is 75 - 100 % and specificity is 60 95 % (Prischl 2017) (Oberhuber 2019).