Meconium peritonitis is a sterile chemical peritonitis developing when meconium leaks into the peritoneal cavity following bowel perforation in the fetal or neonatal period. When meconium contacts peritoneal surfaces, it creates an intense inflammatory response — leading to calcification, fibrosis, and pseudocyst formation. The pathognomonic imaging finding is peritoneal calcification — fine, linear or coarse calcifications are seen on peritoneal surfaces outside the bowel. Causes of perforation include meconium ileus (30-40%), intestinal atresia, volvulus, internal hernia, and idiopathic causes. It can be detected on prenatal ultrasound: intra-abdominal calcification, ascites, dilated bowel loops, and/or meconium pseudocyst are seen. Peritoneal calcification on AXR is diagnostic for the neonate. Treatment varies based on the cause and activity of perforation — conservative observation for sealed perforations, surgical repair for open perforations.
Age Range
0-0
Peak Age
-
Gender
Equal
Prevalence
Rare
Meconium peritonitis develops as a consequence of fetal bowel perforation. During perforation, meconium from the bowel lumen leaks into the peritoneal cavity. Meconium contains bile salts, pancreatic enzymes (trypsin, lipase), cholesterol crystals, and squamous cells — these components create intense chemical irritation on the peritoneum. Damage to peritoneal mesothelial cells initiates an inflammatory cascade: macrophage infiltration → cytokine release → fibroblast proliferation → collagen deposition (fibrosis) → granulation tissue formation. Calcification forms through dystrophic calcium salt deposition on necrotic tissue and denatured proteins — calcium phosphate and calcium carbonate crystals organize. This process occurs over weeks and becomes visible on radiograph. Pseudocyst forms as an extraluminal meconium collection with a fibrotic wall — the fibrous capsule encapsulates and confines the meconium. Ascites results from peritoneal inflammation causing fluid transudation. The perforation may seal off in utero — in this case the neonate may be asymptomatic and diagnosis is made by incidental calcification. If perforation remains open, peritonitis symptoms develop postnatally.
Calcifications seen on peritoneal surfaces outside the bowel on abdominal radiograph are pathognomonic for meconium peritonitis. Calcifications may be fine linear, plaque-like, or nodular and are seen in flanks, pelvic floor, beneath the liver, and below the diaphragm. In the neonate, peritoneal calcification almost always indicates meconium peritonitis as other causes are extremely rare in this age group.
Calcifications on peritoneal surfaces outside the bowel are seen on AXR — this finding is pathognomonic for meconium peritonitis. Calcifications may be fine, linear, plaque-like, or nodular. They are typically seen in the flanks, pelvic floor, beneath the liver, and below the diaphragm. Scrotal calcification may result from meconium descending into the scrotum through a patent processus vaginalis — this finding strongly suggests meconium peritonitis in male neonates. Wall calcification may indicate the perforation site.
Report Sentence
Extraluminal calcifications on peritoneal surfaces are seen on AXR; this finding is consistent with meconium peritonitis; further evaluation for underlying bowel perforation is recommended.
Prenatal ultrasound reveals hyperechoic foci (calcification) in the fetal abdomen — may be seen scattered or clustered on peritoneal surfaces. Ascites (anechoic free fluid) frequently accompanies. Dilated bowel loops suggest obstruction. Meconium pseudocyst appears as a calcified-walled, mixed echogenic (meconium + fluid) mass. Prenatal detection of these findings is critical for postnatal surgical planning.
Report Sentence
Hyperechoic calcified foci on peritoneal surfaces and ascites are seen in the fetal abdomen on prenatal ultrasound; findings are consistent with meconium peritonitis.
Meconium pseudocyst appears as a cystic mass with calcified or fibrotic wall and heterogeneous internal content (meconium + fluid + debris). Size is variable — from a few cm to large masses. Wall calcification is seen as a hyperechoic rim and may create posterior acoustic shadowing. Internal content may be echogenic (thick meconium) or mixed. The pseudocyst is located in the extraluminal peritoneal space — may or may not have connection to bowel. May displace adjacent bowel by compression effect.
Report Sentence
An intra-abdominal cystic mass with calcified wall and heterogeneous content (meconium pseudocyst) is seen; findings are consistent with meconium peritonitis.
CT clearly demonstrates high-density calcifications (>100 HU) on peritoneal surfaces. CT best evaluates the distribution of calcifications, pseudocyst size, and bowel obstruction pattern. Meconium pseudocyst appears as a mass with calcified wall and heterogeneous density content. Free fluid (ascites) is seen. CT can also evaluate the perforation site and possible vascular complications (mesenteric vessel thrombosis).
Report Sentence
High-density calcifications on peritoneal surfaces and a calcified-walled pseudocyst are seen on CT; findings are consistent with meconium peritonitis.
Scrotal calcification seen in male neonates results from meconium descending into the scrotum through a patent processus vaginalis. Scrotal calcification can be detected on AXR or scrotal radiograph. This finding is highly specific for meconium peritonitis, though other causes exist (such as gonadal teratoma), it is very useful in clinical context evaluation.
Report Sentence
Scrotal calcification is seen, consistent with meconium passage through a patent processus vaginalis in meconium peritonitis.
Criteria
Perforation sealed, widespread fibrotic adhesions and calcification, no pseudocyst
Distinct Features
Most common type, usually detected as incidental calcification in asymptomatic neonate, surgery generally not needed
Criteria
Calcified-walled pseudocyst formed, meconium confined within cyst, perforation sealed or connected to cyst
Distinct Features
May cause bowel obstruction by mass effect, surgery may be needed, calcified-walled mass on AXR/US
Criteria
Active/open perforation, widespread peritonitis, ascites, sepsis signs
Distinct Features
Most severe type, requires emergent surgery, neonate appears septic, worst prognosis, pneumoperitoneum may be seen
Distinguishing Feature
Meconium ileus is distal ileum obstruction without perforation; soap bubble sign + microcolon present; no peritoneal calcification (unless complicated); meconium peritonitis may be a complication of meconium ileus
Distinguishing Feature
Neuroblastoma/teratoma may be confused with meconium pseudocyst as calcified mass; neuroblastoma is of extrarenal origin with elevated urinary catecholamines; teratoma contains fat and bone; differentiation by US and CT
Distinguishing Feature
In the neonate, peritoneal calcification almost always indicates meconium peritonitis; other causes of peritoneal calcification (TB peritonitis, peritoneal carcinomatosis) are practically not seen in this age group
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
3-monthManagement of meconium peritonitis is determined by the status of perforation. In sealed off perforations (fibro-adhesive type), the asymptomatic neonate can be observed conservatively — calcifications carry no clinical significance and may resorb over time. If pseudocyst type is causing bowel obstruction, surgical excision + bowel repair is needed. Generalized type (active perforation) requires emergent laparotomy — perforation repair, peritoneal lavage, and possible bowel resection. In ALL cases, the underlying cause must be investigated — causes such as CF, intestinal atresia, volvulus affect treatment. In CF-associated cases, CF diagnosis is confirmed with sweat test. Prognosis is excellent for sealed perforations, worse for generalized type.
Treatment of meconium peritonitis is surgical, directed at the underlying cause (atresia, volvulus). The fibro-adhesive type usually resolves spontaneously. The cystic type (pseudocyst) may require surgical drainage. The generalized ascites type has the worst prognosis. Prenatal diagnosis is important for delivery planning — referral to a surgical center is needed.