Cystic meconium peritonitis: ultrasonographic features

Meconium peritonitis occasionally occurs as a localized, encysted collection of meconium ranging from a few centimeters in size to huge cysts occupying most of the abdominal cavity. The cyst wall consists of fibrous granulation tissue and the cyst may contain only meconium or may also encase loops of bowel. Gas within the cyst indicates persistent communication between the perforated bowel and the cyst cavity; if the perforation seals over in utero the cyst remains gasless. Calcification is a variable finding. Sonography in two neonates with cystic meconium peritonitis showed well-defined, echogenic masses, one of which contained calcifications and was detected in utero.