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04
Anatomy of the retroperitoneal space – A pictorial review

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Learning Objectives

To understand the normal anatomy of the retroperitoneal space and its compartments using diagrams and CT images
To understand the importance of the renal fasciae in the normal anatomy as well as for the spread of disease.
To illustrate some pathologies that delineate the retroperitoneum.



Background

Anatomy is the foundation of radiology and it is essential for the interpretation of the images obtained.
The retroperitoneum is a complex anatomic space.
The retroperitoneal space is limited anteriorly by the posterior parietal peritoneum and posteriorly by the transversalis fascia, extending from the diaphragm to the pelvis.

The retroperitoneal space contains numerous structures:
   •kidneys, ureters and adrenal glands - perirenal compartment
   •part of the ascending and descending colon - anterior pararenal compartment
   •part of the duodenum - anterior pararenal compartment
   •pancreas - anterior pararenal compartment
   •abdominal vascular axes - posterior pararenal compartment

The division of the retroperitoneum in its compartments is rarely visible in the images of the normal anatomy.
Diseaseprocesses affecting the aforementioned organs will affect the way we view the retroperitoneum, as fluid abutting the fasciae allows for better delineation of the retroperitoneal compartments and fascial divisions.



Imaging Findings

The Retroperitoneum
   •Extra-peritoneal space
   •Superior and inferior borders difficult to define
   •Superiorly communicates with the posterior mediastinum and retrocruralspace at the level of the diaphragm
   •Inferiorly communicates with the pelvis
   •Anterior and posterior limits well defined
   •Anterior limit – posterior parietal peritoneum
   •Posterior limit – transversalis fascia
   • Subdivided by fascial layers into
   •Anterior pararenal space
   •Perirenal space
   •Posterior pararenal space


Subdivided in 4 spaces
   •Anterior pararenal space
        •contains parts of the gut (descending and ascending colon), duodenum and pancreas
   •Perirenal space
        •contains the kidney, adrenal gland, proximal ureter and their vascular supply
   •Posterior pararenal space
   •Great vessel space

Subdivided by fascial layers
   •Perirenal fascia
       •Encloses the perirenal space
       •Subdivided in
            •Anterior layer of the perirenal fascia (Gerota’sfascia)
                  •crosses the midline – both perirenal spaces communicate
                  •On CT more easily identifiable on the left
           •Posterior layer of perirenal fascia (Zuckerkandl’sfascia)
                  •adherent to the fascia over the psoas major, iliac fascia and anterior layers of thoracolumbar fascia
                  •thicker and hence more frequently identified on CT


Anterior Pararenal Space
    •most anterior subspace of the retroperitoneum
    •limits
       •anterior – posterior parietal peritoneum
       •posterior – anterior layer of the perirenal fascia (Gerota’sfascia) medially and the lateroconal fascia (Sappey’sfascia) laterally
    •contains
       •parts of the colon, duodenum and pancreas
    •crosses the midline and contacts the contralateral
    •inferiorly communicates with the posterior pararenal space
  
    •Can be further subdivides
       •Pericolic Space
          •more lateral 
          •contains the ascending and descending colon
       •Pancreatoduodenal Space
          •more medial
          •contains part of the pancreas and retroperitoneal duodenum


Perirenal Space
   •limits
       •anterior – anterior layer of the perirenal fascia (Gerota’sfascia) 
       •posterior – posterior layer of perirenal fascia (Zuckerkandl’sfascia)
   •on sagittal evaluation – inverted cone shape 
       •caused by the ascent of the kidneys from the pelvis
       •superior base at the diaphragm
       •apex at the level of the iliac crest
   •contains
       •kidneys, adrenal glands, proximal ureters and their vascular supply
       •bridging septae within the perirenal fat
            •between renal capsule and perirenal fascia, between two points of the renal capsule, between anterior and posterior perirenal fascia and interconnecting septae
   •communicate
       •through the midline with the contralateral
            •small communication between L3-L5 (Kneeland channel), inferior to the origin of the superior mesenteric artery
       •with the bare area of the liver
            •due to the fusion of the anterior layer of the perirenal fascia with the posterior parietal peritoneum
            •allows for retroperitoneal fluid associated with hepatic lesions without significant intraperitoneal fluid (e.g. hepatic laceration)
       •with the subphrenic space on the left


PosteriorPararenalSpace
   • limits
      •anterior – posterior layer of perirenal fascia (Zuckerkandl’sfascia) medially and the lateroconal fascia (Sappey’sfascia) laterally
      •posterior – transversalis fascia
      •medial – psoas muscle
      •lateral – continues as the properitonealfat of the abdominal wall
      •inferior – open to the pelvis
  •does not contain organs, mainly only fat

 

Great Vessel Space
   •considered a separate compartment, though not separated by defined fascia
   •contains abdominal aorta and its branches, inferior vena cava and its afferents, abdominal lymphatic chains and sympathetic trunk


Communications between Spaces
 
   •Perirenal Spaces communicate through the midline
       •level L3-L5 (Kneeland channel)
   •Right Perirenal Space communicates with the bare area of the liver
   •Anterior Pararenal Spaces communicate through the midline
   •Anterior Pararenal Space communicates inferiorly with the Posterior Pararenal Space
      •due to the fusion of the anterior and posterior layers of the perirenal fascia
   •Posterior Pararenal Space is continuous with properitoneal space


Interfascial Planes
  •perirenal fascia are multilaminatedstructures 
  •potential for expansion and formation of spaces
  •pathways for the extension of retroperitoneal disease spread
 
  •Retromesenteric plane(Figure 7)
      •equivalent to the anterior layer of the perirenal fascia
      •between the anterior pararenal space and the perirenal space

  •Retrorenal plane (Figure 8)
      •equivalent to the posterior layer of the perirenal fascia
      •between the perirenal space and the posterior pararenal space
 
  •Lateroconal plane (Figure 9)
      •formed by the dissection of the layers of lateroconalfascia

  •Fascial Trifurcation (Figure 10)

      •location where the retromesenteric, retrorenaland lateroconalplanes communicate

 •Combined fascial plane (Figure 11)

     •better identified on sagittal plane
     •formed by the fusion of the retromesenteric and retrorenalplanes
     •extends to the pelvis
     •anterolateral margins of the psoas muscle
     •contiguous with the pelvic retroperitoneal perivesicaland presacral spaces
 
  •Subfascialplane(not displayed)
     •between the posterior pararenal space and transversalis fascia
     •not consensual


 Conclusion

•The knowledge of the normal anatomic relationships of the retroperitoneal space enables the radiologist to better comprehend the pathological processes affecting this area

•Thickening of the renal fascia is a sensitive but nonspecific indicator of adjacent contiguous disease
   •seen in both inflammatory and neoplastic disorders
 
Renal fascia separating the retroperitoneal spaces are multilaminatedstructures, with the capacity to distend and to become potential spaces / interfascial planes
 
The knowledge of the location of the fascia and retroperitoneal organs enables the radiologist to determine if lesions are of retroperitoneal origin
 
We give a pictographic review of some of the disorders that might affect the way we view the retroperitoneum
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