ANATOMY
We can divide the abdominopelvic cavity into three anatomical spaces: intraperitoneal cavity,
retroperitoneum,
and pelvis.
These spaces are not independent and are communicated with each other through fasciae or anatomical defects.
The retroperitoneum extends from the diaphragm to the pelvis and is bounded anteriorly by the posterior parietal peritoneum and posteriorly,
medially and laterally,
by the transversalis fascia that covers the muscles (lumbar quadratus,
psoas and transverse abdominal).
Within the retroperitoneum,
the anterior and posterior renal fascia form three distinct compartments: the posterior pararenal space,
the anterior pararenal space,
and the perirenal space.
A fourth space surrounds the aorta and the inferior cava vein (great vessels space).
ANTERIOR PARARENAL SPACE
- Boundaries: Between the posterior parietal peritoneum and the anterior renal fascia or Gerota,
being laterally limited by the lateroconal fascia.
Medially there is continuity with the contralateral anterior pararenal space.
Inferiorly fluid may extend to the iliac fossa,
the pelvis and potentially to the rectus sheath.
- Contents: Retroperitoneal segments of the ascending and descending colon,
duodenum,
pancreas (except the tail that is intraperitoneal),
the roots of the small bowel mesentery and transverse mesocolon.
PERIRENAL SPACE
- Boundaries: Limited by the anterior renal fascia or Gerota and posterior renal fascia or Zuckerkandl,
which join anterolaterally forming the lateroconal fascia.
It is shaped like an inverted cone with an apex that extends into the iliac fossa.
It is usually,
but not always,
cut off inferiorly by the fusion of Gerota and Zuckerkandl fasciae and does not extend into the pelvis.
- Contents: Adrenal glands,
kidneys,
proximal ureters,
renal vessels,
fat,
bridging septa and lymphatic vessels that allow the spread of disease to or from adjacent spaces.
- Pathology: Renal cell carcinoma,
lymphoma,
metastases,
sarcoma,
abscess,
haematoma,
urinoma,
lymphangiomatosis,
extramedullary hematopoiesis,
retroperitoneal fibrosis.
POSTERIOR PARARENAL SPACE
- Boundaries: Limited anteriorly by the posterior renal fascia,
the lateroconal fascia laterally,
the transversalis fascia posteriorly and by the psoas muscle medially.
- Contents: Fat,
blood vessels,
and lymphatics.
GREAT VESSEL SPACE
- Boundaries: It is anterior to the vertebral bodies and psoas muscles.
Limited laterally by the perirenal spaces and extends superiorly into the posterior mediastinum.
- Contents: Fat,
aorta and inferior vena cava (IVC).
- Pathology: Retroperitoneal fibrosis,
haemorrhage.
Do not exist a continuous anatomical barrier between the peritoneum and the retroperitoneum:
- The anterior pararenal space communicates with the root of the mesentery of the small intestine and the root of the transverse mesocolon.
- Below the level of the kidneys,
the anterior and posterior pararenal spaces unite and communicate inferiorly with the perivesical space and the extraperitoneal compartments of the pelvis.
- The naked area in the liver that contact with the top of the perirenal space.
- The posterior pararenal space is continued laterally forming the properitoneal fat of the abdominal wall and later is communicated with the contralateral posterior pararenal space.
- The great vessels space does not have fasciae,
so a pathology can extend to other retroperitoneal spaces.
- The lateroconal fascia is continued in the flanks and merges with the parietal peritoneum.
The perirenal fascia it is formed for multiple layers with interfascial planes,
creating potential spaces,
and the knowledge of this interconnections can help to understand the routes of extension in the retroperitoneal processes:
- Retromesenteric interfascial plane (RMP): is a potentially expansile plane located between the anterior pararenal and perirenal spaces.
It crosses the middle line being a potential way of communication between both sides.
The fluid in this plane is often attributed by mistake to the anterior pararenal space.
The RMP extends through the subperitoneal space to the right inferior coronary ligament and the liver,
and it communicates with the liver hilum.
- Retrorrenal interfascial plane (RRP): is a potentially expansile plane located between the perirenal and posterior pararenal spaces.
It does not cross the midline because it is interrupted by the great vessels space.
The collections in the anterior pararenal space and the RMP may extend to the RRP.
On the left side,
the RRP and the perirenal space extend to the left diaphragm.
* The RMP combines with the RRP inferiorly to form the combined interfascial plane or fascial trifurcation (FT),
which extends into the pelvic retroperitoneum and into the pelvis,
being a route for the spread of some pathologies.
- Lateral conal interfascial plane (LCP): is a potentially expansile plane located between the layers of the lateroconal fascia.
It communicates with the RMP and RRP in the fascial trifurcation.