Peritoneum and Peritoneal Cavity

10.1055/b-0034-87871

Peritoneum and Peritoneal Cavity

**Table 2.59 Clear peritoneal fluid (ascites)**
Diagnosis	Findings	Comments
Normal finding	Small pouches of fluid between bowel loops or in Douglas pouch.	Visible in up to 22% of normal children. Also in patients in peritoneal dialysis, with ventriculoperitoneal shunts, in postovulation period.
Pitfalls		Fluid-filled bowel loops. Fluid-filled rectum.
Fetal hydrops	Also pleural and pericardial effusion, subcutaneous edema.	Clinically evident.
Urinary ascites	Uni-/bilateral dilatation of excretory system. Caused by lower obstruction and upper rupture: urethral valves, neurogenic bladder, extrinsic mass.	Caused by lower obstruction and upper rupture: urethral valves, neurogenic bladder, extrinsic mass.
Cardiac disease	Dilatation of hepatic veins with monoor biphasic flow on Doppler US.	In latter phase, hepatic veins are narrowed.
Portal hypertension Fig. 2.129	Intrahepatic portal obstruction: neonatal hepatitis with portal cirrhosis, biliary atresia. Extrahepatic obstruction: atresia, compression.	Look for other findings: heterogeneous hepatomegaly, splenomegaly, portosystemic shunts.
Trauma	Small amounts of fluid are normal after blunt trauma.	If amount of fluid is larger, look for organ injuries: liver, spleen, kidney, mesentery, bowel, bladder.
Hemorrhage	Subacute and chronic hemorrhage, after cloth formation and sedimentation may resemble clear fluid.	Usually after trauma, ruptured ovarian cyst, or hydrometrocolpos.
Peritoneal carcinomatosis	Ascites with peritoneal or mesenteric nodules. The primary tumor is usually depicted.	In peritoneal seeding of gastric, pancreatic, or ovarian tumors. Also lymphoma.

**Fig. 2.129 Ascites.** Free anechoic peritoneal fluid is seen in a neonate with biliary cirrhosis and portal hypertension.

**Table 2.60 Dense peritoneal fluid (ascites)**
Diagnosis	Findings	Comments
Hemorrhage	In acute phase, blood is echogenic (US) and hyperattenuating (CT).	After blunt trauma with solid organ injury, cystic mass rupture, etc.
Biliary ascites		After perinatal trauma or surgery.
Chylous ascites	Low-level echoes (US) and hypoattenuating (CT).	Postprandial, after birth, trauma, or surgery. In filariasis, lymphangiectasia.
Secondary peritonitis Fig. 2.130 Fig. 2.131	In late cases, the origin of peritonitis may be not clearly depicted.	In appendicitis, pancreatitis, pelvic inflammatory disease, perforation of hollow viscus.
Primary peritonitis Fig. 2.132a, b	Ascites with peritoneal engorgement that enhances with contrast (CT). Loculations can be seen.	Bacterial, TB, viral.
Meconium peritonitis Fig. 2.133a, b, p. 224	Proximal bowel obstruction. Dense fluid. Calcifications.

**Fig. 2.130 Peritonitis secondary to free perforation of acute appendicitis.** Sagittal US image of pelvis in a 3-year-old boy shows echogenic fluid surrounding the hyperechoic omentum and intestinal loops over the distended bladder. The appendix was not identified, even at surgery.

**Fig. 2.131 Douglas fluid.** Sagittal US image shows a small amount of hyperechoic free fluid in the pouch of Douglas (arrowhead) in a patient with suspected acute appendicitis. This finding suggests this diagnosis, particularly if seen after 48 hours of evolution, even if the appendix itself is not depicted. In this case, surgery confirmed the diagnosis of acute appendicitis.

**Fig. 2.132a, b Tuberculous peritonitis.** US abdominal scans at mesogastrium (a) and RLQ (b) show the thickened hyperechoic omentum located in contact with the whole anterior abdominal wall. In (a), the omentum is seen homogeneously hyperechoic, whereas in (b) it is more heterogeneous. Slightly echogenic ascites is present. Note that in appendicular peritonitis, the omentum is in contact with the appendicular area, not the abdominal wall.

**Fig. 2.133a, b Meconium peritonitis.** Transverse abdominal US through the right upper quadrant (RUQ) (a) and in mesogastrium (b). Ascites is present. In (a), the meconium deposits are seen in subdiaphragmatic area. In (b), meconium is seen beside the left kidney. Also in (b), the bowel loops are outlined by a thin hyperechoic meconium rim.

**Table 2.61 Localized fluid collections** See **Tables 2.64** and **2.66** (abdominal cystic masses) and free peritoneal air (pneumoperitoneum) in neonate.
Diagnosis	Findings	Comments
NEC	Air dissecting colonic wall with free air in late stages.	Seen in premature infants.
Gastric perforation	Large amount of peritoneal air.	Spontaneous idiopathic perforation in premature infants.
GI tract obstruction	Obstruction is evident.	Usually in low tract obstruction: imperforate anus, Hirschsprung disease, meconium ileus.
Extra-abdominal air dissection	From pneumomediastinum.
Iatrogenic		After laparotomy, thermometer injury in rectum, traumatic tube placement in stomach or bladder.

**Table 2.62 Free peritoneal air (pneumoperitoneum) in neonates**
Diagnosis	Findings	Comments
GI tract perforation	Location of air depends on location of perforation.	After gastric or duodenal ulcer, appendicitis, inflamed Meckel diverticulum.
Extra-abdominal air dissection	From pneumomediastinum.
Iatrogenic	After surgery.
Fistulas		To abdominal wall, GI tract, vagina.
Air-producing intra-abdominal infections	Gas may be contained or disseminate to peritoneum.	In emphysematous infections: appendicitis, pancreatitis, other origin abscesses, etc.

**Table 2.63 Peritoneal calcifications**
Diagnosis	Findings	Comments
Tumors
Neuroblastoma	Over 30% of tumors show coarse or stippled calcifications. Most common locations: paravertebral and suprarenal.	Up to 70% of tumors have calcifications on CT exam.
Teratoma	Coarse calcifications, but also frequently well-defined structures, like teeth.	Also fat density can be depicted in radiograph.
Wilms tumor	Mass effect in the renal fossa, with curvilinear or phlebolithic calcifications in 15%.	Calcifications are not stippled.
Hepatoblastoma	Heterogeneous, coarse, ill-defined calcifications in 12%–30%. In some cases, osseous matrix.	Also, hemangioendothelioma may show fine granular calcifications. Hepatoma has no calcium on radiograph.
Mesenteric cysts	Rim calcification.
Inflammatory—trauma
Calcified abscesses	Frequent in paravertebral tuberculous abscesses, less frequent in bacterial.	Secondary to spondylodiscitis.
Tuberculous peritonitis	Small foci of calcifications in multiple locations.	Usually other signs of TB (in most cases pulmonary) are not seen.
Calcified hematoma		Usually posttrauma.
Hydatid cysts	Eggshell-like calcification, most of them located in the liver, but also splenic, peritoneal.	Caused by calcification of external (adventitial) layer. In endemic areas.
Meconium peritonitis	Small flecks of calcification scattered throughout abdomen. Lineal calcifications along inferior surface of liver.	In neonates, with obstructive signs following birth. Pathologic obstetric US. Also accompanied with meconium pseudocysts.
Peritoneal dialysis	Lineal calcifications of peritoneum.	Deposit of calcium-binding protein after several years of dialysis.
Lymph nodes	Single or multiple, usually in central or lower abdomen, rounded or irregular.	After a wide variety of infections: TB, salmonella, other bacteria.
Other
Phlebolith	Small, rounded calcifications with central radiolucent dot.	Frequent in pelvis.
Renoureteral calculi	Irregular or rounded calcifications of variable sizes, located superimposed to the kidneys and to the ureteral trajectory.	Uric acid stones only show calcification with CT.
Biliary calculi	Rounded calcification, usually multiple and sometimes with central low-density area.
Foreign bodies Fig. 2.134	Located anywhere in the GI tract, but more frequent in physiological low-caliper areas: antrum, ileocecal.	Wide variety of sizes and shapes. Ingestion has sometimes been noted.
Enterolith	In chronic constipation, usually with anorectal anomalies.	Formed by deposition of calcium over inspissated feces.
Appendicolith	Usually laminated and located in RLQ, but may be present also in right flank, pelvis, etc.	Present in 7%–15% of appendicitis (usually complicated).
Lithiasis in Meckel diverticulum	Similar to appendicolith, but usually centrally located.	Diff cult DD with appendicolith (much more frequent).