400 A new notable compression source of left renal vein entrapment: the Right Renal Artery

Abstract Background and Aims Clinically, left renal vein (LRV) entrapment is almost equivalent to the nutcracker phenomenon (NCP). However, there is still much uncertainty and debate about the prevalence of NCP and its diagnostic criteria. As a particular type of LRV entrapment, the LRV compression by the right renal artery (RRA) was primarily reported as case reports. The study was designed to investigate the RRA-sourced LRV compression in two selected patient cohorts. Method The cross-sectional study consecutively selected 38 hospitalized kidney patients diagnosed with membranous nephropathy (Renal group) and 305 peripheral vascular inpatients or outpatients (Non-renal group) in the Second Affiliated Hospital of Harbin Medical University in China from November 2018 to March 2023. The patients with computed tomography (CT) of renal veins or abdominal aorta were included in both groups if axial CT imaging could visualize the renal vessels and was with regular and adequate layer thinness to perform multiplanar reconstruction analysis. Any potential situations that might cause positional or course changes in proximal RRA or LRV due to pathological reasons were excluded from the study. The CT data of LRV compression by different anatomical sources, including but not limited to RRA, was analyzed. Results With other anatomical compression sources excluded, there were 22.58% (7/31) and 20.00% (5/25) LRVs compressed by the RRAs in the Renal and Non-renal groups, respectively, with no significant difference (p = 1.0). The distal segments of the LRVs compressed by RRAs have a significantly larger lumen area than those of non-compressed veins (p < 0.01 in both groups). The overall incidence of NCP was calculated as 10.71% (6/56). Complex compressions, namely those LRV compressions by another adjacent structure besides RRA, coincided in 7.14% of the total cases (4/56). Conclusion Our study showed that it was not rare for the proximal RRA to compress the end of LRV. The detected incidence of RRA-sourced LRV compression was twice that of the entrapment related to the superior mesenteric artery, the mainstay of NCP. Though this finding came from two relatively small subject populations, it challenged the present connotation of LRV entrapment. Further repetitive studies are needed to test if such a phenomenon prevails in different populations, including healthy individuals. Legends for all figures: Green thick arrows, RRA; green arrowheads, superior mesenteric artery (SM