RETROPERITONEUM

Question 1

What is the RMP/RMS?

Answer 1

• The retromesenteric plane is a potentially expansile plane located between the anterior pararenal space and the perirenal space (Fig 12a).
• It communicates across the midline and is a major source of fluid spread in patients with pancreatitis. The presence of fluid in the retromesenteric plane is often erroneously attributed to the anterior pararenal space.
• Figure 12. Retroperitoneal anatomy.
  
  • (a) Diagram shows the anterior (APS) and posterior (PPS) pararenal spaces, perirenal space (PS), retromesenteric plane (RMP), retrorenal plane (RRP), and lateral conal (LP) planes.
  • (b) Axial CT image, obtained in a 76-year-old man with duodenal perforation who underwent endoscopic retrograde cholangiopancreatography, shows a large amount of dissected retroperitoneal air outlining the retromesenteric plane (RMP)— which connects across the midline—and retrorenal plane (RRP).
    
    • The anterior pararenal space (APS) is mostly free of gas.
    • Note that it is possible for disease to extend from the posterior pararenal space (PPS), through the quadratus lumborum muscle (arrow), and into the subcutaneous space, the site of an inferior lumbar hernia as well as the GreyTurner sign, which manifests as lateral abdominal discoloration in patients with severe pancreatitis.
    • Extravasated air has dissected into the Morison pouch (MP), a finding indicative of abrupt accumulation of air or fluid that crosses the peritoneal and retroperitoneal spaces.
  • (c) Axial unenhanced CT image shows bilateral lumbar hernias arising from the superior lumbar triangles (arrows).
• https://pubs.rsna.org/doi/pdf/10.1148/rg.322115032

Question 2

retrorenal posterior interfascial space

Answer 2

• Retrorenal Plane
  
  • The retrorenal plane is a potentially expansile plane located between the perirenal space and posterior pararenal space (Fig 12a).
  • 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, which extends into the pelvic retroperitoneum (Fig 13) (14,15).
  • The interfascial plane extends into the pelvis anterolaterally to the psoas muscle and is a route for the spread of some infections, such as tuberculosis.
  • The lateral conal interfascial plane is a potentially expansile space between the layers of the lateroconal fascia that communicates with the retromesenteric and retrorenal interfascial planes at the fascial trifurcation.
• Fig. 1: Drawing of the anatomy of the retroperitoneal spaces at the level of the kidneys.
  • PP: Posterior Parietal Peritoneum,
  • LCF: Lateroconal Fascia,
  • ARF: Anterior Renal Fascia,
  • PRF: Posterior Renal Fascia,
  • PTF: Posterior Transversalis Fascia,
  • APRS: Anterior Pararenal Space,
  • PRS: Perirrenal Space,
  • PPRS: Posterior Pararenal Space,
  • ACS: Aorto-Caval Space,
  • PMP: Premesenteric Plane,
  • LCP: Lateroconal Plane,
  • RRP: Retrorenal Plane.

Question 3

What is the Anterior interfascial retromesenteric plane.

Answer 3

Anterior interfascial retromesenteric plane.

Potentially expansile plane between the anterior pararenal space and perinephric space ; continuous across the midline.

It is an important potential route of contralateral spread of retroperitoneal collections.

Question 4

What is the posterior interfascial retrorenal plane?

Answer 4

Posterior interfascial retrorenal plane.

• Potentially expansile plane between the perinephric space and posterior pararenal space;
• anterior pararenal, peritoneal, or intrafascial fluid may reside within the retrorenal space.

Question 5

What is the Lateroconal interfascial plane.

What does it communicate with?

Answer 5

• Lateroconal interfascial plane.
• Potentially expansile plane between layers of LCF;
• communicates with anterior and posterior interfascial planes at the fascial trifurcation.
• https://epos.myesr.org/posterimage/esr/ecr2008/28533/mediagallery/227131

Question 6

What is the

Combined interfascial plane.

Answer 6

Combined interfascial plane.

• Potentially expansile plane formed by the inferior blending of the anterior renal fascia, posterior renal fascia, and lateroconal fascia
• continues into the pelvis,
• providing a route of disease spread from the abdominal retroperitoneum into the pelvis.

Fig. 2: Sagittal CT image shows inferior fusion of retromesenteric plane (RMP) with retrorenal plane (RRP) to form the combined interfascial plane (CIP). This point creates a route for spread of diseases between the abdominal and pelvic retroperitoneal spaces

Question 7

What does ‘c’ lable?

Answer 7

Combined interfascial plane.

Figure 13. Interfascial spread. (a) Diagram drawn in the sagittal plane shows the inferior fusion of the Gerota (GF) and Zuckerkandl (ZF) fascias, which form the combined interfascial plane (CIP). Although the perirenal space is cut off by the fusion of Gerota and Zuckerkandl fascias inferiorly, it is possible for disease to extend along the combined interfascial plane. (b) Coronal reformatted CT image obtained in a 75-year-old man with nonHodgkin lymphoma shows involvement of the left kidney (*) and perinephric space (black arrow) by tumor and thickening of Gerota fascia (white arrows). (c) Coronal CT image, obtained in the same patient, shows a nodule (arrow) in the combined interfascial plane (arrowhead), a finding indicative of interfascial spread of lymphoma.

https://pubs.rsna.org/doi/pdf/10.1148/rg.322115032

Question 8

What is Happening here?

What is the anatomy involved?

Answer 8

Foramen of Winslow Hernia

Axial CT image obtained in a 48-year-old woman shows the cecum (*) adjacent to the stomach, an unusual position, and passage of the right colic vessels (white arrow) across the foramen of Winslow, findings indicative of a foramen of Winslow hernia.

The foramen is marked posteriorly by the hepatic vessels (black arrow).

The presence of a foramen of Winslow hernia was confirmed at surgery.

https://pubs.rsna.org/doi/pdf/10.1148/rg.322115032

Question 9

What separates the superior and inferior lesser sac?

Answer 9

A schematic diagram showing the lesser sac following the removal of the stomach and the transverse colon. The line of attachment of the transverse mesocolon and the mesentery is shown. The left gastric artery and common hepatic artery project into the lesser sac, raising the left and right gastropancreatic folds, which divide the lesser sac into the superior and inferior recesses. The splenic recess of the lesser sac is seen extending toward the splenic hilum

https://www.researchgate.net/figure/A-schematic-diagram-showing-the-lesser-sac-following-the-removal-of-the-stomach-and-the_fig3_316332115

Sharma, Malay & Madambath, JayanGopinath & Somani, Piyush & Pathak, Amit & Babu, Ramesh & Bansal, Raghav & Ramasamy, Kovil & Patil, Amol. (2017). Endoscopic ultrasound of peritoneal spaces. Endoscopic Ultrasound. 6. 90. 10.4103/2303-9027.204816.

Question 10

Describe the retroperitoneal spaces and their relation ships

Answer 10

Question 11

What is the Fascial trifurcation.

Answer 11

Fascial trifurcation. Site at which the LCF emerges from Gerota fascia; anterior, posterior, and lateroconal interfascial planes communicate at the fascial trifurcation, usually located laterally to the kidney.

Question 12

What does the anterior pararenal space contain?

Answer 12

Anterior pararenal space

Between parietal peritoneum and anterior renal fascia ; contains pancreas and bowel

Question 13

What are the contents of the posterior pararenal space

What does it lie between?

What does it continue as?

Answer 13

• posterior pararenal space
• Between posterior renal fascia and transversalis fascia,
• Contains no organs.
• Fat continues laterally as properitoneal flank stripe.

Question 14

What does the perirenal space contain?

What is it between?

Answer 14

Perirenal space.

Between anterior renal fascia and posterior renal fascia

Contains kidney, adrenal gland, proximal collecting systems, renal vessels, and a variable amount of fat

Question 15

Are the perinephric spaces are closed ________.

The retromesenteric space is _______.

Answer 15

The perinephric spaces are closed medially.

The retromesenteric space is continuous across midline.

Question 16

What are the contents of the perirenal space?

Answer 16

• The PRS contains a rich network of:
  
  • bridging septa,
  • lymphatics,
  • arteries, and
  • veins.
• The perirenal lymphatics communicate with small lymph nodes at the renal hilum, and these, in turn, connect with periaortic and pericaval lymph nodes.
• This lymphatic network provides a potential route of spread for metastatic tumors into the PRS.

Question 17

What are 5 causes of Retroperitoneal Hematoma?

Answer 17

Retroperitoneal Hematoma

Causes

• Anticoagulation
• Trauma
• Iatrogenic
• Ruptured AAA (particularly if >6 cm)
• Tumor:
  
  • RCC
  • large AML

Interventional angiogram identified her primary bleeding source from the left circumflex iliac artery a branch of the external iliac artery and also to a lesser degree from the left L4 and L5 lumbar arteries.

Case Discussion

The patient was emergently transferred to a tertiary center for endovascular embolization. Endovascular angiography revealed the above primary bleeding sources. Each artery received Onyx embolization. Immediate post embolization images showed satisfactory control however her time in ICU continued to be turbulent with dependency on vasoactive medications and continued transfusion of blood products. Repeat abdominal CT angiogram confirmed an increase in the size of her retroperitoneal hematoma. The patient continued to deteriorate falling into multiorgan dysfunction syndrome thought to be contributed by abdominal compartment syndrome. An emergency midline laparotomy was performed. The massive hematoma was evacuated with a rough calculated volume of 10 L. No active arterial bleeding was identified, perhaps from the massive hematoma achieving tamponade. Fortunately, the patient made a full recovery.

Case courtesy of Dr Paul Clarke, Radiopaedia.org, rID: 69556

Question 18

What are the imaging features of Retroperitoneal Haemorrage?

What are the HU for Acute hemorrhage?

Answer 18

Imaging Features

• Dissection through retroperitoneal spaces
• Acute hemorrhage: 40–60 HU
• Hematocrit level

Question 19

Abscess in x = y cause

• anterior pararenal space
• Perirenal space
• posterior pararenal space

Answer 19

Abscess

Location and Causes

• APS (>50%): pancreatitis
• Perirenal space: renal inflammatory disease
• PPS: osteomyelitis

Question 20

What are 3 causes of Retroperitoneal Air?

Answer 20

Retroperitoneal Air

Causes

• Trauma (perforation)
• ERCP
• Emphysematous pyelonephritis

Question 21

8 Causes of retroperitoneal fibrosis

Answer 21

Retroperitoneal Fibrosis

Fibrotic retroperitoneal process that can lead to ureteral and vascular obstruction.

Causes

• Idiopathic (Ormond disease), 70%
• Benign
  
  • Medication:
    
    • methysergide,
    • ergotamine,
    • methyldopa
  • Radiation
  • surgery
  • Inflammation extending from other organs
  • Retroperitoneal fluid:
    
    • hematoma,
    • urine
• Malignant
• Desmoplastic reaction to tumors:
  
  • Hodgkin dis­ease >
  • NHL >
  • anaplastic carcinoma,
  • metastases

Question 22

Which is most likely to cause a desmoplastic reaction and retroperitoneal fibrosis?

NHL, Mets, HL, Anaplastic Ca?

Answer 22

Desmoplastic reaction to tumors:

• Hodgkin dis­ease >
• NHL >
• anaplastic carcinoma,
• metastases

Question 23

What medications cause retroperitoneal fibrosis?

Answer 23

• Methysergide
• Ergotamine
• Methyldopa

Question 24

What are the imaging features of Retroperitoneal Fibrosis?

Answer 24

Imaging Features

• Fibrotic tissue envelopes retroperitoneal structures.
• Fibrosis may enhance after contrast administration.
• Extrinsic compression of ureter
• Medial deviation of ureters
• Extrinsic compression of IVC, aorta, iliac vessels
• On T1W MRI,
  
  • fibrous tissue appears hypointense.
  • Active inflammation has an intermediate to hyperintense SI on T2W.

Case courtesy of Dr Luke Danaher, Radiopaedia.org, rID: 17435

Question 25

SIGN What is the test? What is the sign? What is the diagnosis?

Answer 25

Intravenous urogram shows medial deviation of the middle part of both ureters. https://emedicine.medscape.com/article/458501-overview

Question 26

What is the dx?

Answer 26

Pelvic Lipomatosis * Abnormal large amount of fatty tissue in pelvis compressing normal structures. Unrelated to obesity or race. * May occur with IBD of rectum. Imaging Features * Elongation and narrowing of urinary bladder **(pear shape)** * Elongation and narrowing of rectosigmoid * Large amount of fat in pelvis Case courtesy of Dr Mostafa El-Feky, Radiopaedia.org, rID: 56420

Question 27

What are the differentials for a pear shaped bladder?

Answer 27

Causes of a pear-shaped bladder include: * pelvic fluid * pelvic haematoma: * the original description of the inverted pear-shaped bladder was in patients with pelvic trauma and haematoma; it can also be seen in patients receiving anticoagulation therapy * bilateral lymphoceles: * may develop following radical pelvic lymph node dissection * extravasated urine / bilateral urinomas * abscess * pelvic lipomatosis: * non-malignant overgrowth of fat around the bladder that causes an inverted pear-shaped bladder * vascular dilatation * bilateral iliac artery aneurysms; upright pear-shape * inferior vena cava (IVC) occlusion causes formation of collateral vessels that compress the bladder and form an inverted pear-shaped bladder; in the days of intravenous urograms, the combination of a renal mass and a pear-shaped bladder was a red flag for renal cell carcinoma involving the renal vein and IVC 2 * symmetric lymph node enlargement, e.g. lymphoma, leukaemia * psoas muscle hypertrophy upright pear-shape: especially in people with narrow pelvises a ratio of the (sum of the widths of the two psoas muscles):(the pelvic width) \>0.98 predisposes to bladder compression 2,3,6 Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 36785

Question 28

\_\_\_\_\_ percent of **retroperitoneal tumors** are ____ and are usually \_\_\_\_\_at diagnosis.

Answer 28

**Ninety** percent of retroperitoneal tumors are **malignant** and are usually **very large** (10–20 cm) at diagnosis.

Question 29

What are the different categories of Retroperitoneal tumours?

Answer 29

Types * **Mesodermal tumors** * Lipoma * liposarcoma * Leiomyosarcoma * Fibrosarcoma * MFH * Lymphangiosarcoma * Lymphoma * **Neural tumors** * Neurofibroma, schwannoma * Neuroblastoma * Pheochromocytoma * **Embryonic tumors** * Teratoma * Primary germ cell tumor

Question 30

What are the 13 different types of retroperitoneal tumours? 3 categories

Answer 30

* Types * Mesodermal tumors * Lipoma * Liposarcoma * Leiomyosarcoma * Lymphangiosarcoma * Lymphoma * Fibrosarcoma * Malignant fibrous histiocytoma * Neural tumors * Neurofibroma * Schwannoma * Neuroblastoma * Pheochromocytoma * Embryonic tumors * Teratoma * Primary germ cell tumor

Question 31

What are the 3 histological types of this pathology? which is the most common?

Answer 31

Liposarcoma * Fat-containing retroperitoneal tumors range in spectrum from lipomas (benign) to liposarcoma (malignant). Imaging Features * Nonhomogeneity with focal higher density structures (i.e., greater than –25 HU) is strong evidence of a liposarcoma. * Tumors are classified histologically as: * lipogenic, * myxoid, * pleomorphic. * Myxoid and pleomorphic tumors are most common and may demonstrate little or no fat on CT. Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 7623

Question 32

Who is this tumour most common in? What is the most common site for this tumour?

Answer 32

* **Leiomyosarcoma** * **Imaging Features** * Large mass * Typically large areas of central necrosis * Heterogeneous enhancement * Retroperitoneal leiomyosarcoma is one of the commonest primary retroperitoneal neoplasms. * **The retroperitoneum is considered the most common extrauterine site for leiomyosarcoma.** * Epidemiology * **They are more common in women.** * Case courtesy of Dr Safwat Mohammad Almoghazy, Radiopaedia.org, rID: 54211