CT OF THE MESENTERIC VASCULAR ANATOMY

Background: To evaluate the appearance of the arrangement of the super ior mesenteric artery (SMA) and superior mesenteric vein (SMV) on comp uted tomography (CT) in normal patients and in patients with abdominal masses. Methods: One hundred seventy-seven consecutive abdominal CT e xaminations of 143 adults and two children were reviewed. The relation ship of the SMV to the SMA was recorded at four locations: the beginni ng of the mesenteric vessels and levels 3 cm, 6 cm, and 9 cm caudad to the beginning. The relationship of the SMV to the SMA was divided int o four quadrants in relation to the SMA: I, ventral right or directly ventral; II, dorsal right or directly right; III, dorsal left or direc tly dorsal; and IV, ventral left or directly left. Results: In the beg inning of the SMV-SMA complex and levels 3 cm, 6 cm, and 9 cm caudal t o the beginning, the SMV was located in quadrant I in 146, 84, 69, and 43 examinations, in quadrant II in 31, 93, 71, and 27 examinations, i n quadrant III in zero, zero, five, and three examinations, and in qua drant IV in zero, zero, nine, and 15 examinations, respectively. The c ases with SMV inversion had neither malrotation nor adjacent tumor com pression. All the cases with an adjacent tumor-induced compression of the SMV-SMA complex had a normal SMV-SMA relationship. Conclusion: In the first 3 cm, the SMV is always to the right of the SMA. Caudal to t he level of 6 cm, the SMV may be located to the left of the SMA withou t evidence of malrotation, A midgut nonrotation is more likely to be p resent when a proximal SMV inversion is coexistent with a rightward di rection of the proximal jejunal vessels. A hypothetical depiction of t he step-by-step change of the SMV-SMA relationship during embryologic development may explain the arrangement patterns of the mesenteric ves sels in normal rotation and midgut nonrotation.