Multiple renal arteries commonly occur, and the occurrence rate of the left side varies in different populations from 25–40%, meanwhile that of the two renal arteries was from 13.5–31.1%, 28.0% for male, 16.4% for female [2]. Generally, the etiology of the variation is the abnormal embryological development. Based on the view point of Felix [3], three sets of arteries supply the developing embryo: the caudle, middle, and cranial lateral mesonephric arteries. Normally, the left renal artery develops from one of the middle lateral mesonephric artery, and the other arteries degenerate. The presence of multiple left renal arteries derives developmentally from the persistence of two or more lateral mesonephric arteries. This applied to our case, two lateral mesonephric arteries persist to exhibit the two left renal arteries.
The occurrence rate of multiple renal veins was less than that of renal arteries and the range was 1–8% on the left side. The variation of left renal vein was classified into four types: circum-aortic renal vein, retro-aortic renal vein, additional renal vein and primary tributaries [4]. According to the classification, two types presented in our case: the retro-aortic type and the additional renal vein type. The course of the retro-aortic renal vein in our case was oblique, this phenomenon was in accordance with the description of the classification, however, it was different to the horizontal course of the study by Bhagavath P et al [5]. Embryologically, the left renal vein derives from postcardinal, subcardinal and supracardinal veins. During development, anastomosis of interposteriorcardinal, intersubcardinal, sub-posteriorcardinal, intersupracardinal, and sub-supracardinal vein forms, the intersubcardinal anastomosis and the medial part of the right and left sub-posteriorcardinal anastomosis form the ventral portion of the circum-aortic venous collar, the lateral sub-supracardinal anastomosis forms the lateral portion, and the intersupracardinal anastomosis completes the dorsal portion. Normally, the interposteriorcardinal and intersupracardinal anastomoses degenerate, the ventral portion of the circumaortic venous collar persists to be the normal left renal vein. If the dorsal portion persists and the ventral portion disappears, the retro-aortic renal vein displays. One left renal vein usually remains, if two or more left renal veins persist, the additional renal vein type presents. In this case, the presence of two left renal veins was attributing to the remaining of two renal veins. The etiology of the oblique course of the retro-aortic renal vein is associated with the development of the inferior vena cava which is from the paired postcardinal, subcardinal and supracardinal veins like renal vein. The infrarenal segment of the inferior vena cava develops from supracardinal vein, and the renal segment from the sub-supracardinal anastomosis [6]. In our case, the site of the retro-aortic renal vein draining into inferior vena cava was at the level of lower pole of left kidney. Embryologically, the supracardinal vein as the common origin for retro-aortic renal vein and the infrarenal segment of the inferior vena cava, the retro-aortic renal vein coursed obliquely and inferiorly from the initial site of left renal hilum to the terminal site at the level of lower pole of left kidney of the infrarenal segment of inferior vena cava.
The occurrence rate of the genital artery originating from the renal artery was 14% reported by Notkovitch [7]. The genital artery and the renal artery are associated developmentally with the common origin of the mesonephric artery [3, 8]. The renal artery develops from the abovementioned middle lateral mesonephric artery, and the genital artery is from the caudal mesonephric artery. Generally, the cranial and middle mesonephric arteries supplying the genital gland degenerate, only one caudal mesonephric artery remains to be the left genital artery. The degeneration of the caudal mesonephric artery and persistence of the middle mesonephric artery cause the abnormal origin of the left genital artery from the left renal artey.
The left genital vein and the left renal vein have the common developmental origin, namely, the subcardinal vein. After the presentation of the left renal vein, the distal portion of the subcardinal vein remains to form the left genital vein, and other subcardinal veins degenerate. Dysplasia of the subcardinal vein causes the abnormal drainage of the renal vein draining into the genital vein [8]. To our knowledge, this is the first report on the abnormal drainage pattern. This drainage pattern makes the renal blood return more difficult and affect the renal function to develop complications such as renal edema and hematuria. Furthermore, the lower renal vein in our study presented a tiny venous vessel and an arcuate course, this phenomenon was not easily detected in the retroperitoneal region during surgery or venography, this can result in intraoperative bleeding and postoperative hematoma formation.