Retroperitoneum

The retroperitoneum is the part of the abdominal cavity that lies between the posterior parietal peritoneum (anteriorly) and anterior to the transversalis fascia (posteriorly). It is divided into three spaces by the perirenal fascia and is best visualised using CT or MRI. It is C-shaped on axial cross section with convexity projecting anterior in the mid-line. 

There are 5 compartments. 

• lateral compartments divided into 3 spaces by renal fascia 
  • anterior pararenal space
  • perirenal space
  • posterior pararenal space
• great vessel compartment from T12 to L4/5 between perirenal spaces (defined in the recent literature ^{2, 3} )
• posterior compartments containing psoas muscles which joins iliacus (note that this is behind transversalis fascia)

Perirenal space

• inverted cone shape with base resting on diaphragm and point directing towards the pelvis
• boundaries 
  • anterior and posterior renal fascia continuous with each other (fascia of Gerota and Zuckerkandl respectively)
    • anterior renal fascia blends anteriorly with connective tissue around aorta and inferior vena cava
    • posterior renal fascia (thicker, two lamina) blends with quadratus lumborum fascia 
      • superficial lamina is made up of lateroconal fascia which extends anteriorly and attaches to peritoneum
• contents 
  • kidney, adrenal gland, renal pelvis, proximal ureter, renal hilar vessels, lymph nodes, fat 
• relations
  • upper right perirenal space communicates with retrohepatic space at bare area of the liver
  • posterior pararenal space related posteriorly
  • anterior pararenal space related anteriorly
  • theroretical communication between both perirenal spaces known as the Kneeland channel in front of the aorta and inferior vena cava  

Anterior pararenal space

• boundaries 
  • posterior parietal peritoneum anteriorly, anterior renal fascia posteriorly and lateroconal fascia (continuation of posterior renal fascia) laterally
• contents
  • duodenum (D2-D4), ascending and descending colon, pancreas, lymph nodes, fat 
• relations 
  • potentially continuous across mid-line, intraperitoneal space anteriorly, perirenal space posteriorly 

Posterior pararenal space

• boundaries 
  • posterior renal fascia anteriorly, transversalis fascia posteriorly 
• contents
  • fat
• relations 
  • communicates with properitoneal space in the anterior abdomen between peritoneum and transversalis fascia
  • communicates potentially with contralateral side
  • communicates with flank laterally (external to lateroconal fascia and deep to transversalis fascia); visualised as flank strip radiologically 
  • opens inferiorly towards pelvis following length of ureter

Great vessel compartment 

• not well-defined by fascial planes
• boundaries
  • laterally: perirenal space and ureter
  • posteriorly: vertebral body, psoas major muscle
  • superiorly: continuous with the posterior mediastinum
• contents
  • aorta, inferior vena cava, fat, lymph nodes

Related pathology

• pneumoretroperitoneum
• retroperitoneal fibrosis