A STUDY OF RENAL VEINS

Address for Correspondence: Dr. N. B. S. Parimala, MBBS, M. D. (Anatomy), Associate Professor, Department of Anatomy, Balaji Nivas, 48-11/8-8, currency nagar main road, Near swarna Residency Apartments, Vijayawada, Krishna district, (AP), INDIA-520008. Mobile no: 9440791896 E-Mail: nbsparimala @gmail.com Introduction: Accessory renal arteries are more frequently reported than veins. Multiple renal veins tend to be relatively common on the right and quite rare on the left side where as arteries have common incidence on both sides .The configuration patterns of the renal vein tributaries were classified as type IA (one upper and one lower tributary), type IB (type IA plus a posterior tributary); type IIA (more than two tributaries, for example, upper, middle and lower); type IIB (type IIA plus a posterior tributary); type III (any of the above classifications plus another additional vein). Materials and Methods: The study was conducted during 2010 to2016, in 60 adult embalmed cadavers (60 right and 60 left kidneys) allotted for routine undergraduate dissection. Renal veins and their variations were studied and recorded carefully during dissection of retroperitoneal area. Observations and Results: In the present study accessory renal veins were seen only on right side. Additional veins were not observed on left side. Instead, extra hilar formation of left renal vein by the union of 2 or 3 tributaries was observed. Accessory right renal vein was observed in 3 out of 60 kidneys (5%). Extra hilar formation of left renal vein by the union of segmental renal tributaries, left supra renal vein and left gonadal vein was observed in 9 out of 60 kidneys (15%).Left renal vein with Retro aortic course seen in 5 out of 60 (8.3%) and circum aortic course in 2 out of 60 (3.3%) was also observed. Discussion and Conclusion: Incidence of accessory right renal vein was variable from 33% to as low as 0.3 % in previous studies but in the present study it is 5%. The cause of such variations was explained embryologically owing to the complexity in the development of renal veins along with inferior vena cava. Variations in the renal veins are clinically unpredictable but pose technical difficulty during renal transplantation. Hence the study was undertaken.


INTRODUCTION
the right one, with the inferior vena cava in its usual position, on the right side of aorta [1].
Accessory or supernumery renal vessels are a common observation reported by many authors previously. Accordingly, accessory renal arteries tend to be twice as common as renal veins. The incidence was almost equal on both Renal vein originates from the confluence of a variable number of primary tributaries that emerge from the kidney. The cardinal venous system is represented on the right side by the vena cava itself and by the left renal vein on the opposite side. The left renal vein is longer than Bhanu Sudha Parimala Namburu. A STUDY OF RENAL VEINS. sides in case of arteries. Multiple renal veins were quite rare (1 percent) on the left, but relatively common (27.8 percent) on the right [2][3][4].
Thorough knowledge of normal and variant anatomy of renal vessels is essential in performing many retroperitoneal surgeries, venographic procedures, lymphadenectomy, renal cell cancer with venous extension, in staging of testicular tumours and placement of inferior caval filters [5].
Variations in the number of renal veins are clinically unpredictable but pose technical difficulty during renal transplantation [6].

OBSERVATIONS
The configuration patterns of the RV tributaries were classified as below based on previous study [7] Type IA -one upper and one lower tributary Type IB -type IA plus a posterior tributary Type IIA -more than two tributaries, for example, upper, middle and lower Type IIB -type IIA plus a posterior tributary Type III -any of the above classification plus another additional vein.
A significant prevalence of anatomical variations in the left renal vein of about 92% and the presence of multiple right renal veins about 8.0 to 9.7% of cases was described in literature [9].
The cause of such variations including the origin, course & termination of renal veins can be explained on embryological basis.
A complex embryological process is responsible for the development of inferior vena cava from 3 primitive cardinal veins i.e; posterior, supra and subcardinal that appear, anastamose and regress in a sequential manner.The inferior vena cava thus developed has 4 segments called hepatic, suprarenal, renal and infrarenal of which renal and infra renal segments were the segments where abnormalities tend to occur most frequently [10].
At the time of formation of renal segment of inferior vena cava from the right sub cardinal vein due to shifting of venous arrangement, each kidney was drained by multiple mesonephric veins representing ventral and dorsal tributaries, the confluence of which resulted in the formation of corresponding renal vein. Accessory renal veins are common on the right side due to persistence of such mesonephric veins and rare on the left side as major part of the venous system regresses on that side [11].
The primary (lobar) tributaries of the renal vein, i.e. upper, middle, lower, posterior and additional renal veins (when present) were identified and used as the basis for classification. Accessory renal vein was considered as a normal variant where the extra renal vein drains into inferior vena cava separately in addition to the renal vein proper [7]. (Fig: 3, 4) Double renal veins are commonly reported. Triple and quadruple renal veins are very rarely reported. In a study, among the 33 specimens with accessory right renal veins 28 (17.9%) had two renal veins and five (3.2%) had three of them [12].
In a study conducted on 30 cadavers (60 renal veins) supernumery renal veins were seen on right side in 10 cadavers. Nine Out of those 10

DISCUSSION
The most common venous variant seen in approximately 15-30% of individuals was Supernumerary renal veins [8].
had single right supernumery renal vein and only in one side double supernumerary veins were reported. Single supernumery left renal vein was seen [13].
In the present study double renal veins were observed only on the right side. Triple renal veins i.e.; presence of 2 accessory renal veins was not observed in this study.
Comparison of incidence of accessory renal veins (right &left side) with previous studies was shown in Table: 3.  [20]. Comparison of percentage of left renal vein (LRV) variations was shown in Tab 4.
The incidence of accessory right renal veins was very low in the present study when compared with previous studies.
At the hilum renal veins lie anterior to renal artery after their formation from segmental veins. The longer (7.5cm) left renal vein receives two tributaries namely left suprarenal vein and left gonadal vein ,crosses the abdominal aorta superficially to open into left lateral aspect of inferior vena cava whereas the shorter right renal vein(2.5cm) opens into it directly and does not receive the corresponding tributaries [18].
A rare case of three renal veins draining the right kidney and separately joining the inferior vena cava with inferior renal vein receiving right testicular vein was reported earlier [19].
Pick & Anson [2] reported incidence of right testicular vein as a tributary of right renal vein as 15% where as in the present study only 1.6% incidence (1/60 right kidneys) (Fig: 4) was reported.
The portion of left renal vein which is associated with aorta develops from anastomoses between cardinal system of both sides in the form of a network having both pre aortic and retro aortic limbs. In case of normal left renal In the present study incidence of retro aortic left renal vein is comparable to that of Dhar and Ajmani [17] and that of circum aortic left renal vein with Pick and Anson [2].Unlike other studies [21][22][23][24][25][26] the incidence of retro aortic left renal vein is more than that of circum aortic left renal vein in the present study.
The retroaortic or circumaortic renal vein may be compressed between the aorta and the vertebral body, which is called posterior nutcracker.
The clinical features of such phenomenon may vary from asymptomatic microhematuria to severe pelvic congestion [29].
A knowledge of the variations of renal vascular anatomy has importance in exploration and treatment of renal trauma, renal transplantation, renovascular hypertension,renal artery embolization, angioplasty or vascular reconstruction for congenital and acquired lesions, surgery for abdominal aortic aneurysm and conservative or radical renal surgery [30].
With the advent of laparoscopic renal transplantation superseding the routine open surgical method detailed and thorough knowledge of renal veins becomes essential because of the rarity of occurrence of variations, difficulty in identification, particularly when located in retro Bhanu Sudha Parimala Namburu. A STUDY OF RENAL VEINS.
aortic area and the potential haemorrhage that occurs when injured during the surgical procedures [15].Hence the study was undertaken.

CONCLUSION
In the present study accessory renal veins were seen only on right side, Prehilar formation of renal vein was predominant on left side. In addition retro aortic and circum aortic course of left renal vein was also observed.
The study stresses the use of advanced non invasive radiological techniques with thorough knowledge of renal vascular anatomy. The variations of renal veins like multiple renal veins, retro and circum aortic left renal vein though uncommon should be borne in mind before radiological evaluation and any surgical procedure particularly transplantation.