Unusual Drainage of the Bifurcated Left Renal Vein Into a Dilated Lumbar Azygos Vein and Inferior Vena Cava

Exceedingly rare incidence of a double inferior vena cava (IVC) with azygos continuation of left IVC

Key Clinical Message

Because of the complex embryonic origin of the abdominal venous structures, IVC and azygous systems can show numerous and even previously unreported anatomical variations and anomalies. Also, evaluating major vascular structures should not be dismissed in non-contrast-enhanced CT as it can provide valuable information about these structures.

Abstract

Double IVC is a rare occurrence of IVC anatomical variations and congenital anomalies. Herein, we discuss a case of a very rare type of double IVC that has not been reported in the literature before. A non-contrast-enhanced CT study was performed for a 34-year-old patient who visited our ER to evaluate for urolithiasis, during which two IVCs were noted. Each renal vein joined the ipsilateral IVC at a perpendicular angle. Unusually, the right IVC was formed from the confluence of both left and right common iliac veins (CIV), and the left IVC-Instead of crossing the midline at the renal veins level and reuniting the right IVC-cranially contributed to the azygos vein formation and caudally joined the left CIV. Also, there were some small communicating veins between the two IVCs and the left gonadal vein was slightly dilated before suggesting a reflux from the left renal vein (LRV). A complimentary doppler ultrasound exam confirmed the diagnosis and revealed a left-side varicocele. Although rare cases of hemiazygos continuation and interiliac connections of left-side IVC in the cases of double-IVC have been reported previously, a complete confluence of CIVs is rare. The main differential diagnosis is retro-aortic left renal vein (RLRV) type IV which seems to have an oblique course. Radiologists and surgeons should expect previously unreported variations in the vena cava system. Furthermore, reviewing the main abdominal vasculature should not be dismissed in non-contrast CT exams.

Chronic elevation of renal venous pressure induces extensive renal venous collateral formation and modulates renal function and cardiovascular stability in rats

Acutely increased renal venous pressure (RVP) impairs renal function, but the long-term impact is unknown. We investigated whether chronic RVP elevation impairs baseline renal function and prevents exacerbation of renal dysfunction and cardiovascular instability upon further RVP increase. RVP elevation (20-25 mmHg) or sham operation (sham) was performed in rats. After 1 wk (n = 17) or 3 wk (n = 22), blood pressure, RVP, renal blood flow (RBF), renal vascular conductance (RVC), and glomerular filtration rate (GFR) were measured at baseline and during superimposed RVP increase. Chronic RVP elevation induced extensive renal venous collateral formation. RVP fell to 6 ± 1 mmHg at 1 wk and 3 ± 1 mmHg at 3 wk. Baseline blood pressure and heart rate were unaltered compared with sham. RBF, RVC, and GFR were reduced at 1 wk but normalized by 3 wk. Upon further RVP increase, the drop in mean arterial pressure was attenuated at 3 wk compared with 1 wk (P < 0.05), whereas heart rate fell comparably across all groups; the mean arterial pressure-heart rate relationship was disrupted at 1 and 3 wk. RBF fell to a similar degree as sham at 1 wk (-2.3 ± 0.7 vs. -3.9 ± 1.2 mL/min, P = 0.066); however, at 3 wk, this was attenuated compared with sham (-1.5 ± 0.5 vs. -4.2 ± 0.7 mL/min, P < 0.05). The drop in RVC and GFR was attenuated at 1 and 3 wk (P < 0.05). Thus, chronic RVP elevation induced by partial renal vein ligation elicits extensive renal venous collateral formation, and although baseline renal function is impaired, chronic RVP elevation in this manner induces protective adaptations in kidneys of healthy rats, which attenuates the hemodynamic response to further RVP increase.