8 Peritoneal Cavity and Retroperitoneal Space


8 Peritoneal Cavity and Retroperitoneal Space

Rick van Rijn

In this chapter, the peritoneal cavity and the retroperitoneal space will be discussed. The focus is solely on the anatomical region and not on the organs within (as these are discussed in separate chapters in this book).

8.1 Normal Anatomy

The peritoneal cavity is the space between the parietal peritoneum and the visceral peritoneum, which covers all the intraperitoneal organs (i.e., the stomach, spleen, gallbladder, liver, and part of the intestines). Approximately 50 mL of fluid is produced daily and circulates throughout the peritoneal cavity in a well defined pattern. During the evaluation of patients with a possible malignancy, it is important to be aware of this pattern of circulation because there are certain areas of stasis where small deposits of, for example, malignancies can be found ( Fig. 8.1 ). Resorption of the peritoneal fluid is predominantly achieved in the subphrenic space.

Fig. 8.1 Graphic representation of the intraperitoneal cavity. Note the direction of the peritoneal circulation and the areas of stasis (asterisks).

It is important to be aware of the fact that whereas in boys the peritoneal cavity is a completely enclosed environment, in girls there is an opening at the level of the ovarian tubes. This can serve as a port of entry for infections such as pelvic inflammatory disease.

The retroperitoneal space is the anatomical region behind the peritoneum, and it contains several organs, which can be remembered with the mnemonic SAD PUCKER ( Table 8.1 ). The retroperitoneal area surrounding the kidneys is divided into three separate parts. The perirenal space is bounded by the Zuckerkandl fascia on the posterior side and the Gerota fascia on the anterior side. This space contains the kidney, adrenal gland, and renal vessels. The anterior pararenal space is bounded posteriorly by the Gerota fascia and anteriorly by the posterior peritoneum. It contains the retroperitoneal duodenum, pancreas, and ascending and descending colon. Finally, the posterior pararenal space, which contains only fat, is bounded by the muscles of the posterior abdominal wall posteriorly and the Zuckerkandl fascia anteriorly.

Table 8.1 Organs contained within the retroperitoneal space


Suprarenal glands


Aorta/inferior vena cava


Duodenum (second and third segments only)


Pancreas (tail is intraperitoneal)




Colon (ascending and descending colon only)







In children, the retroperitoneum can easily be visualized with ultrasonography. In most cases, a graded compression technique and a high-frequency linear transducer can be used ( Fig. 8.2 ).

Fig. 8.2 Normal view of the retroperitoneum with the use of a linear probe in a 2-year-old boy.

8.2 Pathology

8.2.1 Abdominal Vessels


In contrast to adults, pathology of the abdominal aorta in children is rare. There are only a handful of reported cases of congenital anomalies of the abdominal aorta, consisting mainly of atresia and duplication. Other reported pathologies of the abdominal aorta include middle aortic syndrome ( Fig. 8.3 and Fig. 8.4 ), Takayasu arteritis, thrombosis ( Fig. 8.5 ), and aneurysms. Of special interest are the long-term survivors of abdominal neuroblastoma. There have been reports of midaortic syndrome in these children, both in those who have and in those who have not had radiation therapy.

Fig. 8.3 a Ten-year-old boy with a significant narrowing over a short distance of the abdominal aorta. b Digital subtraction angiography shows the narrowing of the abdominal aorta and hypertrophy of the inferior mesenteric artery.
Fig. 8.4 a Eleven-year-old girl with midaortic stenosis (arrow). b Magnetic resonance angiography of the abdominal aorta confirms the finding on ultrasonography.
Fig. 8.5 a, b Premature infant born at 27 weeks. a After placement of an arterial umbilical catheter, a large thrombus has formed in the aorta just below the renal and superior mesenteric arteries. (Courtesy of E. Beek, Department of Radiology, University Medical Center, Utrecht, the Netherlands.) b Color duplex shows obstructed flow in the aorta.

In all of these rare cases, additional imaging with computed tomography (CT) and/or magnetic resonance (MR) imaging is mandatory.

Inferior Vena Cava

Congenital anomalies of the inferior vena cava (IVC) are in general an incidental finding and do not warrant specific follow-up. Because of the complex embryology of the IVC (which comprises four different segments: hepatic, suprarenal, renal, and infrarenal), multiple variants can be encountered. The most common variant is absence of the hepatic segment of the IVC, leading to the azygos continuation ( Fig. 8.6 ; Video 8.6). Other variants include left-sided IVC, double IVC, and anomalous/multiple origins of the veins draining into the IVC ( Fig. 8.7 and Fig. 8.8 ).

Fig. 8.6 a, b Four-day-old girl with an antenatally diagnosed cardiac anomaly and situs inversus. a Sagittal view of the liver shows absence of the hepatic segment of the caval vein. b A cross-sectional view of the retroperitoneum just below the level of the left renal vein shows that the inferior vena cava (arrow) is located to the left of the aorta (open arrow) (see Video 8.6).
Fig. 8.7 Accessory hepatic vein draining segments 5 and 6 in a healthy 13-year-old boy. Note the portal vein (arrow) in relation to the hepatic vein (open arrow).
Fig. 8.8 a, b Thirteen-year-old girl referred for routine follow-up after treatment for a Wilms tumor. a Ultrasound shows an accessory hepatic vein draining segments 5 and 6. b Color Doppler shows the flow from the liver toward the caval vein.

Knowledge of the normal variants of the IVC is important in differentiating between left-sided para-aortic masses and an aberrant IVC and, in cases of percutaneous venous intervention, in IVC stent placement.

Thrombosis/occlusion of the IVC can be encountered in children with central lines and in oncology patients (especially children with Wilms tumor; Fig. 8.9 ; Video 8.9 and Fig. 8.10 ). Ultrasound (US) is in these cases the imaging method of choice. The optimal way to visualize the IVC is from the front. However, in some children this will yield a suboptimal view because of such factors as body shape and gas-distended bowels. In such cases, a lateral approach to the IVC can be used, in which the retroperitoneum is used as a window.

Fig. 8.9 a–c Ten-month-old boy with a Wilms tumor of the left kidney. a Note the grossly abnormal upper and middle poles of the kidney. b Sagittal view shows a large tumor thrombus obstructing the inferior vena cava (arrow). c In the axial view, the thrombus (arrow) can be more difficult to detect.
Fig. 8.10 a–c Ten-year-old boy with a history of treatment for abdominal neuroblastoma. a On ultrasound, absence of the inferior vena cava is noted. b A collateral hypertrophic vein is noted to pass behind the right psoas muscle and drain into the azygos system (see Video 8.9). c Color Doppler shows flow toward the retroperitoneum. (This image shows a significant amount of aliasing, making flow interpretation difficult.)

8.2.2 Lymphadenopathy

Mesenteric Lymphadenopathy

The mesenteric lymph nodes in children are easily visualized, and to the inexperienced radiologist they can look like a pathologic finding. The normal short-axis diameter of the mesenteric lymph nodes is up to 8 mm ( Table 8.2 ). Mesenteric lymphadenopathy is commonly seen in mesenteric adenitis, which is most often caused by a viral infection. However, enlarged, ovoid lymph nodes can also be seen in a significant proportion of otherwise healthy children ( Fig. 8.11 and Fig. 8.12 ). The sole finding of such lymph nodes should not lead to a further work-up. If, however, the lymph nodes show a change in texture, with loss of the hilum and a round, hypoechoic appearance, further analysis is mandatory, either by additional work-up, including cross-sectional imaging, or by biopsy ( Fig. 8.13 ). In patients with large and bulky lymph nodes, further work-up is mandatory. In many cases, a percutaneous or a surgical biopsy must be performed.

Table 8.2 False-positive rate for enlarged mesenteric lymph nodes with varying lymph node threshold size

Threshold size (mm)

No. of enlarged lymph nodes

False-positive rate (%)

≥ 5



> 6



> 7



> 8



> 9



> 10



Source: Reprinted with permission from Karmazyn B, Werner EA, Rejaie B, Applegate KE. Mesenteric lymph nodes in children: what is normal? Pediatr Radiol 2005;35(8):774–777.

Note: In this retrospective study, 61 children (36 boys and 25 girls; mean age, 10.7 years; range, 1.1–17.3 years) underwent noncontrast abdominal computed tomography for the evaluation of suspected or known renal stones; abdominal lymph node size was evaluated. Enlarged mesenteric lymph nodes (short axis > 5 mm) were found in 33 (54%) of the 61 children. The majority of the enlarged mesenteric lymph nodes was found in the right lower quadrant (88%). Based on their findings, the authors stated that a short-axis diameter of > 8 mm might be a more appropriate definition for mesenteric lymphadenopathy in children.

Fig. 8.11 Five-year-old girl referred for follow-up after urologic surgery at the age of 1 year. During routine follow-up, normal lymph nodes are seen.
Fig. 8.12 Screening abdominal ultrasound in a boy with vague abdominal pain shows a normal lymph node (arrow). Note the normal appendix (open arrow).
Fig. 8.13 Ten-year-old refugee from sub-Saharan Africa. Screening abdominal ultrasound shows multiple lymph nodes with central calcification (arrows). He and both his parents tested positive for tuberculosis.

Retroperitoneal Lymphadenopathy

Unlike mesenteric lymphadenopathy, enlargement of the retroperitoneal lymph nodes should always be regarded as abnormal ( Fig. 8.14 ). Therefore, this finding warrants further follow-up. In children, the most common causes of retroperitoneal lymphadenopathy are malignancies, such as Wilms tumor, neuroblastoma, rhabdomyosarcoma, and malignant lymphoma; however, infectious diseases can also cause lymph node enlargement.

Fig. 8.14 a, b Ten-year-old boy with malaise and weight loss. a Abdominal ultrasound shows a large round lymph node adjacent to the psoas muscle. Note the absence of a normal fat center. b Enlarged lymph nodes near the inferior vena cava. Burkitt lymphoma was diagnosed based on a lymph node biopsy.

On US, lymphadenopathy can be obscured by gastrointestinal gas or, in an increasingly large group of children, obesity. In children with large abdominal tumors, the retroperitoneum can be difficult to visualize. In these children, disease staging with additional imaging (e.g., MR imaging) is mandatory.

Tips from the Pro

  • If the retroperitoneum is obscured by intestinal gas, graded compression, as in the diagnosis of appendicitis, should be applied. Compression should be applied during inspiration.

8.2.3 Intraperitoneal Fluid Collections


Ascites is the accumulation of free fluid in the peritoneal cavity. In healthy girls, a small amount of fluid in the Douglas pouch is a normal physiologic finding ( Fig. 8.15 ). In all other cases, ascites should be regarded as a pathologic finding.

Fig. 8.15 Thirteen-year-old girl referred for follow-up ultrasound (US) for cholelithiasis. US shows a minute amount of physiologic ascites (arrow). This finding should not lead to a further work-up.

The causes of ascites can be differentiated according to whether a transudate, with a low protein content, or an exudate is present. The most common cause of a transudate is portal hypertension, and therefore a transudate is seen in children with cirrhosis and heart failure ( Fig. 8.16 ; Video 8.16). A transudate can also be seen in severe malnutrition (kwashiorkor) and nephrotic syndrome. An exudate is seen primarily in peritoneal metastatic disease and infection ( Fig. 8.17 , Fig. 8.18 , Fig. 8.19 , Fig. 8.20 ; Videos 8.19 and 8.20). There is, however, a large differential diagnosis for the presence of ascites, which is different for neonates ( Table 8.3 ) and children ( Table 8.4 ; Fig. 8.21 and Fig. 8.22 ).

Table 8.3 Causes of neonatal ascites

Hepatobiliary disorders

Genitourinary disorders


Obstructive uropathy

Alpha1-antitrypsin deficiency

Posterior urethral valves

Congenital hepatic fibrosis


Viral hepatitis

Lower ureteral stenosis

Budd–Chiari syndrome

Ureteral atresia

Biliary atresia

Imperforate hymen

Bile duct perforation

Bladder rupture

Portal venous malformation

Bladder injury from umbilical artery catheterization

Ruptured mesenchymal hamartoma

Nephrotic syndrome

Gastrointestinal disorders

Ruptured corpus luteum cyst

Intestinal malrotation

Cardiac disorders

Intestinal perforation


Acute appendicitis

Heart failure

Intestinal atresia

Hematologic disorder


Neonatal hemochromatosis

Chylous ascites

Parenteral nutrition


Metabolic disease


Congenital cutis marmorata telangiectatica

Intravenous vitamin E


Small-bowel duplication

Abdominal trauma


Source: Reprinted with permission from Giefer MJ, Murray KF, Colletti RB. Pathophysiology, diagnosis, and management of pediatric ascites. JPGN 2011;52(5):503–513.

Table 8.4 Causes of ascites in infants and children

Hepatobiliary disorders




Congenital hepatic fibrosis

Wilms tumor

Acute hepatitis

Clear cell renal sarcoma

Budd–Chiari syndrome


Bile duct perforation

Germ cell tumor

Liver transplantation

Ovarian tumor



Gastrointestinal disorders

Metabolic disease

Acute appendicitis

Genitourinary disorders

Intestinal atresia

Nephrotic syndrome


Peritoneal dialysis

Pyloric stenosis

Cardiac disorder


Heart failure

Crohn disease


Eosinophilic enteropathy

Celiac disease

Henoch-Schönlein purpura

Cystic mesothelioma

Chylous ascites

Omental cyst

Intestinal lymphangiectasia

Ovarian cyst

Lymphatic duct obstruction


Lymphatic duct trauma

Systemic lupus erythematosus

Parenteral nutrition extravasation

Ventriculoperitoneal shunt

Vitamin A toxicity

Chronic granulomatous disease

Nonaccidental trauma


Source: Reprinted with permission from Giefer MJ, Murray KF, Colletti RB. Pathophysiology, diagnosis, and management of pediatric ascites. JPGN 2011;52(5):503–513.

Fig. 8.16 a, b Seventeen-day-old male neonate with hepatic failure, as part of multiple-organ failure, and hemorrhages. a Abdominal ultrasound (US) was requested, which showed a homogeneously enlarged liver with ascites (arrow). Laboratory investigation showed a herpes simplex infection. b The portal vein is dilated and hyperechogenic (arrow). During US, the flow in the portal vein was extremely slow (see Video 8.16).
Fig. 8.17 One-year-old girl with an ovarian germ cell tumor. On ultrasound, a significant amount of ascites is seen.
Fig. 8.18 a, b Twelve-year-old boy being treated for a relapse of alveolar rhabdomyosarcoma. The child presented with discomfort and abdominal distention. a On ultrasound, ascites is seen. b Power Doppler shows respiratory-dependent flow of ascites (see Video 8.19).
Fig. 8.19 a, b Sixteen-year-old boy with an exacerbation of known Crohn disease. a Ultrasound shows a thickened and inflamed terminal ileum. b A significant amount of ascites is seen in this patient.
Fig. 8.20 Fifteen-month-old boy admitted to the pediatric intensive care unit with severe gastroenteritis. Abdominal ultrasound shows a significant amount of ascites, which contains small particles. Given the child’s poor condition, an abdominal tap was performed to rule out peritonitis. The ascites was clear on visual inspection, and culture yielded no pathogenic growth (see Video 8.20).
Fig. 8.21 a–f Eight-month-old girl with increased abdominal girth. a Ultrasound shows a diffusely enlarged pancreas with a focal lesion (arrow). b Ascites in the pelvis. c Cystic lesion with septa of unknown origin in the mesentery. d On T2-weighted magnetic resonance imaging, there is a discrete pancreatic lesion of high signal intensity (arrow). e The mesenteric cystic lesion has high signal intensity on T1-weighted imaging (arrow). On T2-weighted imaging, the signal intensity was also high. f Endoscopic retrograde cholangiopancreatography shows contrast extravasation due a laceration in the pancreatic duct. Based on these findings, the diagnosis of child abuse needs to be excluded. The outcome of this investigation is unknown.
Fig. 8.22 a, b One-month-old girl with infantile acute lymphocytic leukemia. a There is hepatomegaly with ascites (arrow). b Ascites. Note the clear depiction of the walls of the small bowel.

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Jun 9, 2020 | Posted by in ULTRASONOGRAPHY | Comments Off on 8 Peritoneal Cavity and Retroperitoneal Space
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