Abdominal cystic masses are frequent findings at ultrasound examination. Renal tract anomalies or dilated bowel are the most common explanations, although cystic structures may arise from the biliary tree, ovaries, mesentery or uterus. The correct diagnosis of these abnormalities may not be possible by ultrasound examination, but the most likely diagnosis is usually suggested by the position of the cyst, its relationship with other structures and the normality of other organs.

Choledochal cysts:

Choledochal cysts represent cystic dilatation of the common biliary duct. Prenatally, the diagnosis may be made ultrasonographically by the demonstration of a cyst in the upper right side of the fetal abdomen. There is communication between the bile duct and the cyst. Absence of polyhydramnios or peristalsis may help to differentiate the condition from bowel disorders. Postnatally, early diagnosis and removal of the cyst may avoid the development of biliary cirrhosis, portal hypertension, calculi formation or adenocarcinoma. The operative mortality is about 10%.

Mesenteric or omental cysts:

These cysts may represent obstructed lymphatic drainage. The fluid contents may be serous, chylous or hemorrhagic. Antenatally, the diagnosis is suggested by the finding of a multiseptate or unilocular, usually mid-line, cystic lesion of variable size; a solid appearance may be secondary to hemorrhage. Antenatal aspiration may be considered in cases of massive cysts resulting in thoracic compression. Postnatal management is conservative and surgery is reserved for cases with symptoms of bowel obstruction or acute abdominal pain following torsion or hemorrhage into a cyst. Complete excision of cysts may not be possible because of the proximity of major blood vessels and in up to 20% of cases there is recurrence after surgery. Although malignant change in mesenteric cysts has been described, this is rare.

Hepatic cysts:

Hepatic cysts are typically located in the right lobe of the liver. They are quite rare and result from obstruction of the hepatic biliary system. They appear as unilocular, intrahepatic cysts, and they are usually asymptomatic, although rarely may show complications such as infections or hemorrhages. Hepatic cysts are found in 30% of the cases of adult polycystic kidney disease.

Intestinal duplication cysts:

These are quite rare, and may be located along the entire gastrointestinal tract. They sonographically appear as tubular or cystic structures of variable size. They may be isolated or associated with other gastrointestinal malformations. Thickness of the muscular wall of the cysts and presence of peristalsis may facilitate the diagnosis. Postnatally, surgical removal is carried out.