When is Doppler of the renal vessels needed?
Arterial hypertension that is difficult to treat with three or more drugs, especially in young patients or, conversely, that occurs suddenly in old age, requires exclusion of a renovascular cause. Renal artery stenosis—narrowing of a vessel by atherosclerotic plaque or fibromuscular dysplasia—triggers the renin-angiotensin cascade and maintains high blood pressure that is not reduced by conventional therapy.
Doppler sonography measures the peak systolic velocity in the renal artery, calculates the renal-aortic ratio and evaluates the shape of the spectrum in the intrarenal vessels: a characteristic flattened curve with a slow rise below the site of narrowing is an indirect but reliable sign of significant stenosis. Additionally, the resistance index is calculated, reflecting the state of the intrarenal vascular bed and having prognostic significance in chronic kidney disease and diabetic nephropathy.
At the same time, the adrenal glands are examined - small glands above the upper poles of the kidneys. Ultrasound reveals space-occupying formations in them, which is important if a hormonally active tumor is suspected as another cause of persistent hypertension. The adrenal glands are located deep, so the quality of the examination greatly depends on preparation: you need to come on an empty stomach and after several days of a diet without gas-forming products.
Ultrasound capabilities
Ultrasound remains the first choice for imaging in almost every situation: it is accessible, safe, does not require radiation, and provides images in real time. It perfectly shows parenchymal organs, fluid formations, walls of hollow organs and soft tissues, and in Doppler mode, blood flow in the vessels.
A separate advantage is the possibility of dynamic tests: the doctor can ask you to strain, change your body position, fill or empty an organ and see how the picture changes. Neither computed tomography nor magnetic resonance imaging provide such an opportunity.
What influences the quality of research
The main enemy of ultrasound is gas: it completely reflects the wave. Therefore, distended intestines can make the pancreas, aorta, and retroperitoneal structures invisible. For the same reason, preparation for examining the abdominal cavity is not a formality, but a condition for a reliable result.
Severe obesity, postoperative scars, bandages and open wounds in the area of interest also have an effect. If the picture turns out to be uninformative, the doctor indicates this in the protocol and recommends an alternative method - computed tomography or magnetic resonance imaging.
Doppler mode
Dopplerography shows the movement of blood: color mapping reflects the direction of flow, spectral analysis measures velocities and resistance indices. This allows you to assess the patency of the vessel, identify stenosis, thrombus, aneurysm, pathological reflux and the nature of the blood supply to the formation.
Increased blood flow in Doppler mode is an important sign of active inflammation or tumor growth, which is why many organ studies are supplemented with Doppler as a mandatory part of the protocol.