By Dr Khanak Nandolia
We are back with a new topic discussion for Radiology Residents with Dr Khanak Nandolia for our FOAM(Free online access medicine) Intiative. Dr Khanak is a Second year resident in DNB Radiology at Rajendra Prasad Govt medical college, Himachal pradesh . You can discuss the topic in the comment section below this blog and also at Freeassociation.in Forums
Learning objectives
To review normal anatomy and communications of the retroperitoneal spaces using schematic illustrations
To illustrate and describe the different types of collections around the kidney.
To understand pathways of disease spread in the retroperitoneal spaces.
Introduction
The retroperitoneum is the compartmentalized space located external to and predominantly posterior to the posterior parietal peritoneum.
About half a century ago, the retroperitoneum was described as a “veritable jungle of strange things” and as a “hinterland of straggling mesenchyme, with vascular and nervous plexuses, weird embryonic rests and shadowy fascial boundaries.”
Since then, a better understanding of the anatomy and pathology of the retroperitoneum has taken place, related largely to cross-sectional imaging techniques.
Overview
Boundaries of retroperitoneal space
Anterior – posterior parietal peritoneum
Posterior – transversalis fascia
Superior – diaphragmatic fascia
Inferior – pelvic brim
Major compartments
Anterior pararenal space
Posterior pararenal space
Perirenal space – the largest of all 3 compartments.
Anterior Pararenal Space
Boundaries:
Anterior – Posterior parietal peritoneum
Posterior – Anterior renal fascia (Gerota fascia)
Lateral – Lateroconal fascia
This space is continuous across the midline. But pathologies remain to one side
Contents are the structures developing from dorsal mesentery.
- Pancreas
- Retroperitoneal portions of the duodenum, ascending and descending colon
- fat.
So, this is a site of a large number of infectious, neoplastic and inflammatory disorders.
Pancreatic process crosses across the midline, pathologies may cross along the midline with it.
The Anterior pararenal space is continuous with the Intraperitoneal space through the root of the small bowel mesentery and through the sites of attachment of the pancreas, liver, duodenum, ascending and descending colon.
Posterior pararenal space
Posterior pararenal space is a thin compartment.
Boundaries
anteromedial – the Posterior renal fascia (Zuckerkandl fascia) and Lateroconal fascia
posterolateral – the Transversalis fascia
Medial – margin of the psoas muscle and quadratus lumborus muscles
opens laterally toward the flank and inferiorly toward the pelvis
This space is closely related to the posterior surfaces of the ascending and descending colon, therefore inflammatory processes originating in these colonic segments easily extend into this space.
The posterior pararenal fat is also adjacent to the junction of the anterior and posterior renal fasciae, so fluid collections coursing within these pathways can track into the Posterior pararenal space.
Perirenal Space (Gerota’s space)
Perirenal space lies in the central compartment of the retroperitoneum, lateral to the lumbar spine.
inverted cone shaped with superolateral to inferomedial orientation.
Boundaries
Anterior – anterior renal fascia ( Gerota’s Fascia)
Posterior – posterior renal fascia ( Fascia of Zuckerkandl)
Superior – it opens into bare area of liver and the mediastinum
Medial – blends with the connective tissue surrounding the great vessels.
Lateral – lateroconal fascia
Laterally the Anterior and the Posterior renal fascia blend, and the posterior layer of the Posterior renal fascia continues anterior-laterally to form the Lateroconal fascia.
Lateroconal fascia continues anterolaterally behind the colon to blend with the Parietal peritoneum.
Midline communication
There is evidence of potential communication across the midline between the two Perirenal spaces anterior to the lower aorta and inferior vena cava and posterior to the Anterior renal fascia at the level of lower lumbar vertebrae (L3-5).
Open inferior ends
Inferiorly this space blends loosely with the iliac fascia and periureteric connective tissue, having its inferior apex open toward to the upper margins of the psoas muscles, ureter, iliac vessels and to the prevesical and presacral spaces.
At this level the perirenal spaces do not communicate.
Thoracic communication
The perirenal space communicates superiorly with the mediastinum through splanchnic foramina of the diaphragmatic crura and through small transdiaphragmatic perforations and lymphatic vessels, providing conduits of potential disease spread between the thorax and the abdomen.
Contents
Kidneys, adrenal glands, proximal collecting system, renal vasculature, perirenal vascular network, lymphatic network and a variable amount of fat.
Largest fat accumulation in the perirenal space medial to the lower pole of the kidney; this is the preferential location where abscesses, hematomas and urinomas may accumulate
The renal parenchyma is tightly wrapped by a rigid Renal capsule composed predominantly of fibrous tissue, which is rarely visualized by CT.
Bridging renal septa
The kidneys are suspended in the Perirenal fat by thin fibrous lamellae, the Bridging renal septa.
These septa divide this space into multiple compartments and can limit distribution of diseases processes.
3 types of these septa are seen.
Group I – cross the perirenal fat and may connect with the renal capsule and pararenal fascia.
Group II – attached only to the renal capsule and course parallel to the kidney .
Group III – connect the Anterior renal fascia with the Posterior renal fascia.
On CT ,they are occasionally visible in the normal perirenal fat but more easily visualized when they become thickened by fluid or by other abnormalities.
Collections around the kidneys
Subcapsular collections – the adjacent renal parenchyma is compressed by the pathologic fluid because of the rigidity of the renal capsule. As a result, the parenchyma becomes flattened and the collection assumes a lenticular shape.
Perirenal collections have a crescentic appearance as they are outside the renal capsule and not limited by it. Fat layer between its inner border and renal parenchyma is preserved.
Interfascial spaces around the kidneys
- The perirenal fluid collections may remain within their compartment of origin being confined by the anterior and posterior renal fascia, adhesions or renal capsule.
- When large volumes of fluid develop rapidly, the capacity of the perirenal space boundaries may be overwhelmed, frequently leading to the recruitment of the potential expansible retroperitoneal fascial planes for decompression.
- These fascial planes also serve as conduit for the spread of fluid, inflammation and tumour.
Interfascial retroperitoneal planes
- According to recent studies, the perirenal fascia is not made up of distinct unilaminated fascia
- It is composed of multiple layers of variably fused embryonic mesentery, creating potential spaces between the retroperitoneal spaces .
- Potential conduits for the spread of pathology.
Retromesenteric plane
- located between the Anterior pararenal space and the Anterior renal fascia.
- Continues superiorly with the diaphragm near to the esophageal hiatus and inferiorly to the pelvis along the anterolateral surface of the psoas muscle,
- Bounded laterally by the descending colon and its mesentery.
- continuous across the midline
- communicates at the fascial trifurcation with the Retrorenal plane and the Lateroconal plane
- Right retromesenteric plane extends superiorly at the level of the right inferior coronary ligament and the bare area of the liver, and it communicates with the liver hilum through the subperitoneal space of the hepatoduodenal ligament .
Retrorenal plane
- Retrorenal plane is situated between the Posterior renal fascia and the Posterior pararenal space.
- It does not cross the midline because it is interrupted by the great vessel space.
- Fluid collections in the anterior pararenal space and the retromesenteric plane may extend to the retrorenal space.
- The retrorenal plane combines with the retromesenteric plane inferiorly to form the combined interfascial plane & extends into the pelvis
Patterns of disease spread in retroperitoneum
Subperitoneal Spread
- The term sub peritoneal spread refers to the spread of fluid or tumour along the peritoneal ligaments (eg, pancreatic inflammation or cancer that spreads along the peritoneal ligaments)
- It involve several contiguous organs
.Interfascial Spread
- Interfascial spread is the spread of fluid within the layers of the retroperitoneal fascia
- It is a common route of disease spread across the midline within the retroperitoneum and from the abdomen to the pelvis, such as along the retromesenteric, retrorenal, and interfascial planes
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