Eur Radiol (2005) 15: 1745–1751 DOI 10.1007/s00330-005-2688-y UROGENITAL Hug Cuéllar i Calàbria Sergi Quiroga Gómez Carmen Sebastià Cerqueda Rosa Boyé de la Presa Américo Miranda Agustí Àlvarez-Castells Received: 19 October 2004 Revised: 10 December 2004 Accepted: 21 December 2004 Published online: 2 March 2005 # Springer-Verlag 2005 Nutcracker or left renal vein compression phenomenon: multidetector computed tomography findings and clinical significance Abstract The use of multidetector computed tomography (MDCT) in routine abdominal explorations has increased the detection of the nut- cracker phenomenon, defined as left renal vein (LRV) compression by adjacent anatomic structures. The embryology and anatomy of the nutcracker phenomenon are relevant as a background for the nutcracker syndrome, a rare cause of hematuria as well as other symptoms. MDCT examples of collateral renal vein cir- culation (gonadal, ureteric, azygous, lumbar, capsular) and aortomesenteric (anterior) and retroaortic (posterior) nutcracker phenomena in patients with no urologic complaint are shown as well as studies performed on patients with gross hematuria of uncertain origin. Incidental observa- tion of collateral veins draining the LRV in abdominal MDCT explora- tions of asymptomatic patients may be a sign of a compensating nut- cracker phenomenon. Imbalance between LRV compression and development of collateral circulation may lead to symptomatic nutcracker syndrome. Keywords Renal veins . Hematuria . Pathologic . Helical computed tomography Anatomic background The development of the fetal venous system transforms a completely symmetrical network into an asymmetrical adult system. The subcardinal veins lie in a plane ventral to the aorta and drain the lower half of the fetal body, while the supracardinal veins, which lie in a plane dorsal to the aorta, drain the upper half. Both systems are interconnected by a venous network that forms a collar around the aorta. Two renal veins (ventral and dorsal) are formed on each side from the regression of these anastomoses. The dorsal ves- sels usually degenerate and the ventral vessels become the renal veins [1]. In the most common adult configuration, the left renal vein (LRV) measures around 7.5 cm, 3 times longer than the right renal vein, and passes in front of the aorta, just below the origin of the superior mesenteric artery (SMA) and above the horizontal course of the duodenum, to meet the inferior vena cava at a slightly higher point than the right vein [2]. The LRV receives the left gonadal (Fig. 1)[1] and ureteral veins and, generally, the left inferior phrenic and the left suprarenal vein. In contrast, the right renal vein only receives the ureteral vein. The ureteral veins connect the renal veins to the gonadal, lumbar and capsular veins with variable anastomoses [3]. This complex left venous net- work displays greater adaptability to flow alterations than the right renal vein. In addition, a retroperitoneal collateral venous network presents insignificant anastomoses with both renal veins [3]. This network includes capsular (Fig. 2), lumbar and H. Cuéllar i Calàbria (*) . S. Quiroga Gómez . C. Sebastià Cerqueda . R. Boyé de la Presa . A. Miranda . A. Àlvarez-Castells Institut de Diagnòstic Per La Imatge, Servei De Radiodiagnòstic, Hospitals Universitaris Vall D’ Hebron, Passeig de la Vall d’ Hebron no.119-129, 08035 Barcelona, Spain e-mail: hugcuellar@terra.es Tel.: +34-93-2746758 Fax: +34-93-4285693