The performance of a sonographic examination (ultrasound examination) of the renal arteries represents an important diagnostic procedure in the evaluation and differentiation of primary essential hypertension from secondary hypertension (primary hypertension – hypertension as an initial disease; secondary hypertension – hypertension as a secondary or secondary disease in the presence of an initial disease). This method of examination is of particular importance in internal medicine because of the high prevalence (frequency of a disease or symptom in a population at a given time) and the difference between the therapeutic measures of primary and secondary hypertension. The proportion of hypertensive patients who have renovascular hypertension (hypertension caused by kidney damage) is between one and four percent. Other studies have shown that the proportion of hypertensive patients with renal hypertension can be as high as 20 percent. Renovascular hypertension can be caused by several primary renal diseases. In addition to atherosclerosis (arteriosclerosis, hardening of the arteries), which particularly affects older men over the age of 60 with other obstructive vascular diseases, there is also the possibility that renal hypertension can be triggered by fibromuscular stenoses. Of crucial importance is the fact that fibromuscular stenosis occurs almost exclusively in the middle third of the renal arteries and frequently affects young women, whereas atherosclerosis-related stenoses are always located at the exit of the renal artery from the aorta (main artery). Because of the different frequencies of stenosis predilection sites, the areas at risk should be targeted in sonography. Thus, in the search for renal stenosis in the workup of hypertension in elderly patients with obstructive vascular changes during ultrasound examinations, sonication of the renal artery outflow from the aorta is of particular importance. In this patient group, renal artery stenosis is expected to occur at the renal artery outflow from the aorta in more than 95% of cases. Accordingly, in adolescents and young adults in whom the primary cause is fibromuscular stenosis, the middle third of the renal artery should be examined sonographically. Types of renal artery stenosis
Fibromuscular stenosis
- Accounts for approximately five to ten percent of existing renal artery stenoses
- Primarily affects female patients younger than 40 years of age
- This form of renal artery sclerosis is preferentially located in the middle or distal third of the renal artery
- As a result of this form of stenosis, poststenotic dilatations (dilations of the vessels, which is located behind the narrowing) occur relatively often
- As primary methods for reconstruction of the renal artery in this present stenosis are PTA (= percutaneous transluminal angioplasty, i.e. dilatation or reopening of narrowed or occluded blood vessels by means of balloon dilatation or other procedures and simultaneous insertion of a stent (vascular support) into the narrowing) and bypass
Arteriosclerotic stenosis
- In contrast to fibromuscular stenosis, this type of stenosis is quite common. If renal artery stenosis is present, the probability that it is arteriosclerotic stenosis is more than 90%. The highest probability of the presence of this type of stenosis is in older male patients, as described earlier.
- Because of the localization at the outlet of the renal artery, poststenotic dilatations are very rare
- Also in arteriosclerotic stenosis, PTA (see the explanation above) represents the most commonly used reconstruction principle. Moreover, there is also the possibility of correcting the stenosis by reinsertion.
Indications (areas of application)
- Clarification of the pathogenesis (disease development) of hypertension – atherosclerotic stenosis, fibromuscular stenosis.
- Differentiation of the degree of stenosis – differentiation between stenoses with obstruction lower than 50%, a higher degree stenosis above 50% and complete occlusions of the artery.
- Follow-up after surgical procedures – ultrasound monitoring should be performed after various renal surgeries, PTAs, and stent insertions
- Suspicion of renal infarction – ultrasound of the renal arteries represents an immediate measure in the diagnosis of renal infarction.
- Aortic aneurysm (permanent widening of the cross-section of blood vessels as a result of congenital or acquired wall changes) – renal artery ultrasonography is performed due to the close local relationship between aneurysm onset and renal artery outlet
- Aortic dissection (a splitting of the wall layers of the aorta, usually caused by a tear of the internal vessel wall) – the use of sonographic diagnosis in aortic dissection occurs as a result of the fact that the renal arteries may be included in the dissection area
- Transplant kidney – by renal artery sonography, among other things, a rejection reaction of the kidney can be detected and assessed.
Only a few years ago, angiography of the renal vessels represented the gold standard in the diagnosis of renal artery stenosis. Since 2006, however, duplex sonography (= combination of B-scan with PW Doppler / Pulse Wave Doppler) is favored as a diagnostic measure. Furthermore, however, it is also possible to check the function and morphology (appearance) of the renal vessels by computed tomography or magnetic resonance imaging. However, if one primarily considers sensitivity (percentage of diseased patients in whom the disease is detected by the use of the procedure, i.e., a positive finding occurs), angiography together with sonography represents the gold standard. Transplant Kidney
- Sonographically, the transplanted kidney can be seen to undergo compensatory enlargement as an adaptation response. The extent of this hypertrophy depends on the age of the donor. Transplants from young patients trigger organ enlargement more frequently and also more pronouncedly. In addition, sonography reveals that the pyramids of the kidney are echo-deficient. Furthermore, the examining physician must pay particular attention to local complications such as a hematoma (clotted blood accumulation) or a urinoma (pathological urine accumulation).
- In general, after transplantation can be divided into vascular and graft dysfunction. Vascular complications include, for example, postoperative occlusion of the anastomosed renal artery or vein and, as a late complication, the occurrence of stenosis of the renal artery. This serious complication occurs in approximately 5% to 25% of all renal transplants. Other late complications include aneurysms and arteriovenous fistulas (connections between artery and vein).
- Detection of renal artery stenosis should be done only by using direct parameters such as flow acceleration in the renal artery course. In acute dysfunction after transplantation, tubular necrosis is often the origin of cell lysis.
