Classification of the drainage patterns of the renal veins.

Variations in the drainage patterns of the renal veins are well described, but existing classifications of the renal veins have deficiencies. This study aimed to formulate a practical classification of their drainage patterns, taking into consideration the number of primary tributaries, additional renal veins and variations. The venous system of 306 kidneys (from 131 males and 22 females) obtained from 100 pairs of resin casts and 53 pairs of plastinated kidneys were analysed. Based on a proposed definition of the renal vein, 3 major types (I, II, III) were identified using the drainage pattern of the primary renal vein tributaries and the renal vein as a basis on both the left and right sides. Type IA occurred most frequently (38.6%) and was commoner on the left. Type IB was the second most frequent (25.2%), with the other types showing lower and similar frequencies (10.1-14.4%). Statistically significant differences were noted between the left and right kidneys with regard to the classification into the different types (P < 0.0001). The proposed classification system is practical and has surgical and uroradiological relevance.