The kidneys lie in the retroperitoneum, surrounded by the perinephric fat between the anterior and posterior layers of the renal fascia (Fig. 1). They lie lateral to and roughly parallel with the lateral border of the psoas. The renal fossa is bounded medially by the psoas muscle, posteriorly by the quadratus lumborum muscle, laterally by the transversus abdominis muscles, and superiorly by the diaphragm. Anteromedially, the kidneys are covered by peritoneum; posteriorly the twelfth rib crosses the left kidney at a 45? angle, with approximately one third or more of the left kidney superior to the inferior margin of the thoracic cage. Organs related to the kidney include the adrenal glands, which are directly superior to the kidney on the right side and anteromedial to the kidney on the left. The upper poles of both kidneys approximate the diaphragm, and the posterior aspect from the medial to the lateral borders is related to the psoas, quadratus lumborum and the transversus abdominis muscle or fascia. Depending on the amount of retroperitoneal fat, the anterior surface of the right kidney may be in contact with the right adrenal gland, the right lobe of the liver, the second portion of the duodenum and the hepatic flexure of the colon. The organs related to the anterior aspect of the left kidney are, from above downwards, the left adrenal gland, the stomach, the pancreas and (on the extreme lateral margin) the spleen and splenic flexure of the colon. In thin subjects the spleen may affect the contour of the left kidney (splenic hump).
Figure 1 The renal fascia. (A) Axial CT section showing anterior and posterior layers of the renal fascia. (B) CT peritoneogram clearly depicting the outline of the layers of the anterior and posterior renal fascia on the right and the location of the perirenal space. (C) Coronal multiplanar reformation (MPR) CT image showing the location of the kidneys in the perirenal space surrounded by the renal fascia.