Meconium pseudocyst 2022-01-22T07:37:48Z A fetal intraperitoneal cystic mass that shows high T1 and low T2 signals in prenatal magnetic resonance imaging is considered pathognomonic of meconium pseudocyst. See Figure 1 of PMID: 19293041. A meconium-containing cyst in the peritoneal space . Meconium pseudocysts form in the presence of meconium peritonitis, which is defined as a sterile peritonitis caused by escape of meconium from the intestinal tract into the general peritoneal cavity during the fetal or perinatal period. When the extruded meconium becomes walled off, it can form a rim-calcified mass representing the meconium pseudocyst. Abnormal fetal gastrointestinal system morphology