The renal artery-aorta angle associated with renal artery plaque: a retrospective analysis based on CT

We retrospectively assessed consecutive patients who underwent abdominal contrast-enhanced CT for screening and evaluating- at a single tertiary center between May 2019 and April 2020. Inclusion criteria: (a) patients with abdominal CT enhancement or CTA from May, 2019, to April, 2020; (b) patients with abdominal CTA from May, 2019, to April, 2020. Exclusion criteria: (a)The bilateral renal arteries were showed apparent structural blur with artifacts, so that the lumen was not evaluated; (b). Laboratory indicators (including glucose, cholesterol, triglycerides, creatinine, BUN, uric acid) were incomplete; (c). The RAS was caused by non-atherosclerosis factors (arthritis, arterial dissection, fibromuscular dysplasia, tumors and so on). A total of 210 patients were finally enrolled in this study, and demographic and clinical data were retrospectively collected from the electronic medical records (Fig. 1). There were 108 male (43%) and 102 female (57%)with an average age of 64.1 ± 11 years old. The lesion group was defined as patients with left or right artery plaque, and the control group was defined as patients without left and right artery plaque. The lesion group was divided into two subgroups (left/right) according to the left or right renal artery of RAP. Right lesion group was divided into R1 and R2 subgroups according to the right renal artery angle A (R1 group if angle A < 61.1° and R2 group if angle A ≥ 61.1°). Left lesion group was divided into L1 and L2 subgroups according to the left renal artery angle A (L1 group if angle A < 57.9° and R2 group if angle A ≥ 57.9°). Hypertension was defined as systolic blood pressure≧140 mmHg or diastolic blood pressure above≧90 mmHg. Diabetes can be diagnosed (Fasting blood glucose is ≧ 7.0 mmol/L, or, random blood glucose and blood glucose of two hours of oral glucose tolerance test are ≧ 11.1 mmol/L). Hypercholesterolemia, hypertriglyceridemia, high serum creatinine, high-BUN and high-uric acid were defined as higher than the upper limit of the laboratory's normal reference range (cholesterol 2.48–5.17 mmol/L, triglycerides 0.57–1.70 mmol/L, creatinine 62–106 μmoI/L, BUN 2.1–7.1 mmol/L, uric acid 2.48–5.17 mmol/L). People who have smoked continuously or cumulatively for 6 months or more were smokers. Abdominal contrast-enhanced CT images demonstrated whether the RAP exits or not and showed the position and property of RAP (2.3). This study was approved and consented by the Ethics Committee of Xidian Group Hospital, and written informed consent was obtained from all participants.

All abdominal contrast-enhanced CT examinations were performed with a 320-slice scanner (Cannon, Japan). These examinations were performed with prior placement of a 20-gauge venous access in a median cubital vein of the right arm and after administration of 80–90 mL of nonionic iodinated contrast medium (Iodine 370 mg I/mL), followed by injection of 30 mL of saline solution at a rate of 3.5 mL/s with the use of a dual-head injector (Irich, Medical). Optimal delay was performed with the automatic intelligent bolus-tracking technique (The tracer was placed in the proximal segment of abdominal aorta with threshold 320HU). Images were acquired with the following protocol: 100–120 kV, automated mA, pitch of 1.5, slice thickness of 0.5 mm, reconstruction interval of 0.5 mm, matrix of 512 × 512, and the total scan time of 182–185 s, the scan range was from the top of the diaphragm to the lower level of the kidney and beyond in a cranio-caudal direction. The dose of radiation was 3 ~ 5 mSv.

All the abdominal contrast-enhanced CT original data were transmitted to an independent imaging workstation (Cannon Vistra6.5, Japan) for post-processing. The primary methods of imaging processing were maximum intensity projection, multi-planar reconstruction, curved-planar reconstruction, and volume rendering [22]. Coronal multi-planar reconstruction (MPR, Fig. 2a) with a 3-mm thickness, Coronal curved planar reconstruction (CPR, Fig. 2b) and volume rendering (VR, Fig. 2c) were used for the evaluation of renal artery. The CT original imaging data were evaluated and analyzed by radiologists with ten years of experience. The position of plaques was documented as the following criteria: (a) the proximal section was defined as proximal 1/3 segment of renal artery trunk; (b) the middle section was defined as middle 1/3 segment of renal artery trunk; (c) the distal section was defined as distal 1/3 segment of main renal artery; (d) the diffuse was defined as two or more segments. The type of the plaque was assessed as the following criteria: calcified plaques–CT value ≥ 130HU, non-calcified plaques–CT value < 130HU, mixed plaques–both non-calcified and calcified plaques [23, 24]. Stable plaque includes calcified plaque and mixed plaque. Unstable plaque includes non-calcified plaque. The diameter of renal artery (proximal, mid, distal) was measured in the axial image. In addition, the angle between the renal artery and the abdominal aorta (angle A) was measured in the coronal MPR image, the angle between the proximal 1/3 segment and the distal 1/3 segment or the rise of the most curved angle (angle B) was measured in the transverse or coronal MPR image, the distance of the bilateral renal artery origin position was measured in the coronal MPR image, the length of the main trunk was measured in the CPR image (Fig. 2b), the vascular variation include accessory renal artery or premature branch (length of the main trunk < 15 mm in CPR), the above parameters were documented by the two radiologists with ten years of experiences. They resolved inconsistent measurement results through repeated measurement (Figs. 3 and 4).

Quantitative data are expressed as mean value ± standard deviation, and qualitative data are expressed as percentage. Statistical methods included the chi-square test, two-sample t-test and logistic regression analysis. The chi-square was used to evaluate the distribution trend of RAP, the proportion of various plaques, the correlation between RAP and renal artery variation, the association between RAP and clinical variables, the difference on the incidence of RAP between the different the renal artery angle A. The two-sample t-test was applied to examine statistical differences on anatomical parameters between groups. Logistic regression analysis was carried out to investigate whether the above statistically different factors are related to the RAP or not. All statistical analyses were performed by using SPSS software (version 25.0). The p-value less than 0.05 were considered statistically significant in this study (FDR corrected).

A total of 210 subjects were included in this study (48.6% female).The average age was 64.1 ± 13.8 years old. Among all patients, 118 patients had RAP, and 92 patients had no RAP. There were significant statistical differences on age, hypertension, hypercholesterolemia, hypertriglyceridemia, and diabetes between the lesion group and control group. The other clinical factors of renal artery between two groups were not significant statistical (p < 0.05 Table 1). Detailed clinical information about the study population was summarized in Table 1.

RAP is the local indicator of systemic atherosclerosis process [2, 12]. This research has confirmed that right RAP is significantly related to age, hypertension and right renal artery angle A, and left RAP is related to age, hypercholesterolemia and left renal artery angle A (Figs. 3 and 4). The possible reasons for this difference are as follows: First. There may exist anatomical and histological slight differences on the structures of wall between left and right renal artery, for this reason, the left renal artery is susceptible to hypercholesterolemia, and the right renal artery is susceptible to hypertension. Second. the starting position of right renal artery is usually slightly higher than that of left renal artery, and the pressure of blood vessel wall gradually decreases from the proximal side to the distal side, therefore, the starting pressure of right renal artery is slightly higher than that of left,blood vessel wall of the right starting position must bear more pressure, so the intima of this position is vulnerable to be damaged, in order to promote plaque formation. Third. The abdominal aorta is on the left, and the position of right kidney is lower than that of the left kidney, hence, the length of the right renal artery trunk is longer than that of the left and the renal artery angle A is smaller than the left one, consequently, blood hypercholesterolemia is vulnerable to deposit in the left renal artery. Finally, the degree of tortuosity of abdominal aorta affects local hemodynamics, which influence the formation of RAP. To the people with the above risk factors, the vessel wall is lack of flexibility and prone to be damaged, the bloodstream is low and the cholesterol is easy to deposit in the wall, which contribute to the formation of plaque [31].

There was no significant difference on the other factors between the two groups. The results are identical with previous researches [32].Our finding that there is no statistical difference on the incidence of RAP between men and women is consistent with previous studies.