ANATOMY
The retroperitoneum is the space that lies between the posterior parietal peritoneum and anterior to the transversalis fascia, and extends from the diaphragm to the pelvis.
It is generally divided by fascias in the anterior and posterior pararenal spaces and the one of the great vessels. Fig. 1
Fig. 1: Drawing of the anatomy of the retroperitoneal spaces at the level of the kidneys. The anterior pararenal space (APRS) is located between the parietal peritoneum (PP) and the anterior renal fascia (ARF) and contains the pancreas (Pan), the ascending colon (AC), and the descending colon (DC). The posterior pararenal space (PPRS) is located between the posterior renal fascia (PRF) and the transverse fascia (TF). The perirenal space (PRS) is located between the anterior and posterior renal fascia. Ao = aorta, IVC = inferior vena cava, LCF = lateroconal fascia.
References: Rajiah et al. (2011). Imaging of Uncommon Retroperitoneal Masses. RadioGraphics 2011; 31: 949–976
Anterior pararenal space:
The anterior pararenal space is the portion of the retroperitoneum that lies between the posterior surface of the parietal peritoneum and the anterior reflection of the perirenal fascia and laterally by the lateroconal fascia. Fig. 1-3
Fig. 2: Sagittal plane of the retroperitoneum showing the anterior renal fascia (ARF - green line) and the posterior renal fascia (PRF - red line). Note its fusion at the infrarenal level.
References: Hospital de trauma y emergencias Federico Abete - Malvinas
Fig. 3: Axial CT scan of the pancreas showing the anterior pararenal space (red line) contains the pancreas (Pan) and the duodenum (Duo), the ascending colon (AC) and the descending colon (DC). Ao = aorta, IVC = inferior vena cava.
References: Hospital de trauma y emergencias Federico Abete - Malvinas
Posterior pararenal space:
Limited by the posterior renal fascia (Zuckerkandl fascia) in front, the transverse fascia behind and medially by Psoas muscle. Fig. 1,4
Fig. 4: CT scan with axial cut level of the kidneys. Illustrating The posterior pararenal space (PPRS) in green, is located between the posterior renal fascia (PRF) red line, and the transverse fascia (TF) orange line.
References: - Hospital de trauma y emergencias Federico Abete - Malvinas
Below the level of the kidneys, the anterior and posterior pararenal spaces join to form the infrarenal retroperitoneal space, which communicates inferiorly with the prevesical space and the extraperitoneal compartments of the pelvis. Fig. 2
Perirenal space:
Limited by the Gerota fascia and the Zuckerkandl fascia which together constitute the renal fascia. It contains the kidneys, renal vessels, adrenal glands, renal pelvis, proximal ureters, lymphatic and perirenal fat. Fig.5
Fig. 5: Axial CT scan shows the perirenal space (PRS) located between the anterior and posterior renal fascia.
References: Hospital de trauma y emergencias Federico Abete - Malvinas
Large vessel space:
It is the fatty region that surrounds the aorta, the inferior vena cava and that supports the vertebral bodies and the psoas muscles.
Between the spaces of the retroperitoneum there are the interfascial spaces (retromesenteric, retrorenal, lateroconal or the combined interfascial space) that can be observed with the presence of large volumes of retroperitoneal fluids. Fig. 6
Fig. 6: Axial CT scan shows the anterior renal fascia (ARF - blue line), the posterior renal fascia (PRF - red line) and its relationship with the lateroconal fascia (LCF - purple line).
References: Hospital de trauma y emergencias Federico Abete - Malvinas
CLINICAL PRESENTATION
Fig. 7
References: Hospital de trauma y emergencias Federico Abete - Malvinas
ETIOLOGY
There are many causes that can be of renal or extrarenal origin. In an extensive review of the literature by Cinman, this author found a 63% tumor cause (30% of malignant tumors and 33% of benign tumors), 25% were associated with vascular disease (polyariarteritis nodosa as the most frequent) and 12% with infectious pathology.(5)
Neoplasic
Angiomyolipoma (6)
- Benign mesenchymal tumor, of slow growth, composed of adipose tissue, vascular and smooth muscle.
- Prone to rupture which in some cases leads to retroperitoneal hemorrhage.
- Asymptomatic and usually do not require immediate treatment. Its presence is associated with tuberous sclerosis. Fig. 8, Table 1
Table 1: - Hospital de trauma y emergencias Federico Abete - Malvinas
Fig. 8: CT axial A-B note the dense linear images in the right perirenal space as signs of bleeding (circle), the kidney enhances reaching a density similar to that of the blood. C - D. hematoma in the infrarenal space (arrow), this related to a rounded image of adjacent fat density (arrowhead).
In this patient the presence of an angiomyolipoma was confirmed.
References: Hospital de trauma Federico Abete
Clear cell carcinoma (7)
- Malignant cortical tumor, characterized by cells with clear cytoplasm due to its lipid content, has a large vascular compromise that usually infiltrates the venous system and extends to the vena cava.
- Hypervascularized (Enhance with contrast in us, CT and MRI).
- In the images, they have a variety of aspects from solid and relatively homogeneous to markedly heterogeneous with areas of necrosis, cystic changes and hemorrhage.
Vascular (8)
- Nodose polyarteritis: Vasculitis is the most common cause of vascular etiology, polyarteritis nodosa is a systemic vasculitis of medium and small vessels which is associated with aneurysm formation, which can be complicated by rupture and subsequent bleeding.
- Renal artery aneurysm: are uncommon, their prevalence is unknown. The etiology is usually related to fibromuscular dysplasia, arteriosclerosis of the renal artery, and may be congenital, associated with arteritis, or with a traumatic history. Less common causes are Syphilis or Tuberculosis. They are usually asymptomatic, however in some cases they can cause flank pain (15%), hematuria (30%), hypertension (55%), etc (9). Aneurysmal rupture is rare but it is a lethal complication. Fig. 9,10
- Coagulation disorders: Extremely rare cause of spontaneous rupture of the kidney, however possible in a patient under hemodialysis with platelet dysfunction and deterioration of the renal structure (4).
- Arteriovenous malformations.
- Segmental infarction.
- Splenoportal short circuits due portal hypertension.
- Hemodialysis.
- Treatments with anticoagulants. Fig. 11, 12
Fig. 11: Axial CT show spontaneous right renal subcapsular hematoma in anticoagulated patient. A. Note that the hematoma density is higher (asterisk) than that of the renal parenchyma. B. The kidney enhances reaching a density similar to that of the hematoma (red circle). C. The excretory phase shows no commitment from the collecting system.
References: Hospital de trauma Dr. Federico Abete
Fig. 12: A. Coronal CT of the same patient as in Fig. 8. shows the hematoma that compresses the kidney (arrowhead). B. Sagittal CT shows slight thickening of the lateroconal fascia (arrow)
References: Hospital de trauma Dr. Federico Abete
Infection
- Pyelonephritis Fig. 13
Fig. 13: Patient with an overinfected renal cyst secondary to pyelonephritis and renal lithiasis. A. CT without contrast showing the enlarged right kidney with lithiasis (arrow) B. C. Nephrogenic phase. D. Shows heterogeneous right perirenal hematoma, with areas of greater density in declining portion (hematocrit sign), the asterisk indicates active bleeding.
References: Hospital de trauma y emergencias Federico Abete - Malvinas
- Abscesses
- Tuberculosis
Others
-Kidney Cysts Fig. 14,15
Simple renal cysts are the most frequent benign renal lesions. Cysts, usually asymptomatic, can however grow and become complicated. The spontaneous rupture of a known renal cyst, documented by radiological images, occurs exceptionally (11-14). Table. 2
Table 2: - Hospital de trauma y emergencias Federico Abete - Malvinas
Fig. 14: Axial CT shows enhanced cyst (Bosniak IIF) in the left kidney (red arrow).
References: Hospital de trauma y emergencias Federico Abete - Malvinas
Fig. 15: Nephrogenic and late phase of the same patient in Fig.14 (four years later), shows a subcapsular perirenal hematoma (red asterisk) as a result of the rupture of the renal cyst.
References: Hospital de trauma y emergencias Federico Abete - Malvinas
- Hydronephrosis
- Lithiasis (2) Fig. 13
DIAGNOSIS
The diagnosis begins with clinical suspicion but its confirmation is achieved through complementary tests such as ultrasound and computed tomography (CT) that confirm the presence of retroperitoneal hematoma and its extension.
Ultrasound has quick access and can show perirenal collections with heterogeneous internal echoes, depends on the operator and has a sensitivity of 50%. CT is the complementary test of choice to detect hemorrhages with a sensitivity of 100% and, in most cases, allows to establish the etiological diagnosis of presumption.
Among the tomographic findings we can find:
Sentinel Clot Sign
In the CT without contrast, the hemorrhage has a density of 35-45 Hounsfield units (HU) in the hyperacute state and more than 60 HU in the acute state (that decrease over time). There are denser areas in the bleeding site and nearby, than in the rest of the blood collection. Fig. 16
Fig. 16: Coronal CT shows dysmorphic right kidney, with perirenal hematoma that displaces the liver. The asterisk indicates the area of greatest density adjacent to the kidney (sentinel clot sign). The source of the bleeding was a renal cyst.
References: Hospital de trauma y emergencias Federico Abete - Malvinas
Active contrast leak
On contrast CT, sometimes the place of active bleeding can be seen as an area or point of greater density than free or coagulated blood, between 85 and 300 UH. Fig. 10
Fig. 10: A. Arterial phase axial CT, shows the left kidney displaced anteriorly by the hematoma in the perirenal space (white arrow). B. Nephrogenic phase axial CT, shows an increase in contrast extravasation (arrowhead) and the size of the hematoma that extends to the anterior pararenal space (asterisks).
References: Hospital de trauma y emergencias Federico Abete - Malvinas
Hematocrit sign
In hematomas of multiple locations, a liquid-liquid level, denser (on CT) or echogenic (on ultrasound) in the area of decline appears after a variable time, due to the deposition of cellular elements from blood. Fig. 17
Fig. 17: Coronal CT same patient of Figure 10. The left kidney shows a subcapsular hematoma of heterogeneous density (hematocrit sign) (red asterisk). Intraperitoneal free fluid (white asterisks) is also observed.
References: Hospital de trauma y emergencias Federico Abete - Malvinas