Evaluation of Renal Cortical Stiffness and Renal Venous Hemodynamics Using Shear Wave Elastography and Color Doppler Ultrasonography in Asymptomatic Patients With a Retroaortic Left Renal Vein

BACKGROUND: This study investigated renal cortical stiffness and renal venous hemodynamics using shear wave elastography (SWE) and color Doppler ultrasonography (CDUS) in asymptomatic patients with Type 1 retroaortic left renal vein (RLRV). Associations among left renal vein (LRV) peak systolic velocity (PSV), renal cortical stiffness, and the CT-derived LRV diameter ratio were also evaluated. METHODS: Fifty-nine asymptomatic adults with Type 1 RLRV were included. Right- and left-sided renal measurements were compared within the same patients. Renal cortical stiffness was assessed by SWE, and renal venous PSV was measured by CDUS. On contrast-enhanced CT, the LRV diameter ratio was calculated as the anteroposterior diameter at the aortovertebral level divided by that at the proximal one-third of the renal vein. Patients were stratified according to an LRV diameter ratio of ≥ 0.5 or < 0.5. Group comparisons and Spearman correlation analyses were performed. RESULTS: (IQR, 25.85-32.44). LRV PSV was significantly higher than right renal vein PSV (23.33 vs. 22.00 cm/s, p = 0.014), and left renal cortical SWE values were significantly higher than right-sided values (9.09 vs. 7.22 kPa, p < 0.001). LRV PSV was higher in patients with an LRV diameter ratio ≥ 0.5 than in those with a ratio < 0.5 (p = 0.03). LRV PSV showed positive correlations with left renal cortical SWE (ρ = 0.323, p = 0.012) and the LRV diameter ratio (ρ = 0.325, p = 0.012). No significant correlations were observed between the LRV diameter ratio and left renal cortical SWE or between age/BMI and the evaluated parameters. CONCLUSIONS: In asymptomatic patients with Type 1 RLRV, left renal venous PSV and renal cortical stiffness were higher than right-sided values. The modest positive correlation between LRV PSV and left renal cortical SWE suggests an association between renal venous flow characteristics and renal cortical biomechanical properties. The correlation between the LRV diameter ratio and PSV further suggests an association between the CT-derived anatomical parameter and renal venous flow characteristics. These findings are hypothesis-generating and do not establish RLRV-related renal injury. Larger prospective studies with healthy controls and functional renal assessment are warranted.