*Ultrasound Division, ASL Roma B, Rome, Italy; albanacerekja@hotmail.it
**Department of Pediatrics, Policlinico Umberto I, Università “La Sapienza” Rome, Italy;
***Ultrasound Division, Ceprano Hospital, Ceprano, Italy.

Introduction

Meconium is the content of fetal gastro-intestinal tract. If the meconium spills out through a bowel perforation into the peritoneal cavity, it is irritative and elicits an inflammatory response referred to as meconium peritonitis.

Perforation and leakage of the meconium usually occurs just proximal to an area of bowel obstruction. For example, meconium peritonitis can occur proximal to an atretic segment of small bowel or proximal to a meconium plug in a fetus with cystic fibrosis. In some cases the cause of meconium leakage cannot be determined.

Fetal response to the chemical peritonitis produces a number of intraperitoneal findings occurring after the intraperitoneal meconium leakages. There may be an abnormal fluid collection in the peritoneal cavity, either free (ascites) or bounded within a meconium cyst. The fluid meconium content calcifies, and subsequently, intraperitoneal calcifications may develop, either on the serosal surface of the bowel or liver or in the wall of a meconium cyst. If the processus vaginalis is patent at the time of perforation, calcification may also be seen in the scrotum.

Case report

This is a case of a 26-year-old patient (G2P1) that was seen at 20 weeks of her gestation with non-contributive personal or family history. First ultrasound examination was performed elsewhere at 13 weeks and was reported to be normal.

Our examination found scattered hyperechoic spots on the peritoneum of the liver and spleen surface and adjacent anterior abdominal wall. The gallbladder appeared small. Amniotic fluid volume was at the upper limit for the gestational age (AFI 20 cm). There was no evidence of fetal ascites or dilated bowel loops or other anomalies. Placental thickness was within normal limits for gestational age. A few hyperechoic spots were also seen within the right scrotum suggesting a meconium periorchitis. The findings led us to the diagnosis of simple meconium peritonitis.

Maternal serology for toxoplasmosis, cytomegalovirus and parvovirus B19 was negative. Amniocentesis for aneuploidies and cystic fibrosis investigation was suggested but parents declined these tests.

The patient was scanned again at 31 weeks. Amniotic fluid volume was at the upper limit (AFI 19 cm), fetal growth was at 50 percentile and there was no bowel dilatation. The gallbladder looked normal. Tiny hyperechoic spots scattered on the serosal surface were barely visible.

A male neonate was born by cesarean section (due to previous cesarean section) at 39 weeks. His birthweight was 3050 grams and Apgar scores was 9/9 at 1/5 minutes respectively. Physical examination revealed a healthy newborn. The abdomen was not distended and meconium passed on the day 2. An abdominal ultrasound performed on day 3 revealed only some hyperechoic spots on the Glisson’s capsule.

Sweat-chloride test for cystic fibrosis was negative. Karyotyping resulted in normal karyotype (46, XY). 18 months after delivery the bay is thriving well.

Videos 1, 2, 3, 4, and 5 : Ultrasound at 20 weeks show hyperechoic spots scattered on the serosal surfaces of the fetal abdomen.

Images 7-11: Ultrasound at 31 weeks shows hyperechoic spots scattered on the serosal surfaces of the fetal abdomen.

Videos 6, 7: The videos show hyperechoic spots scattered on the serosal surfaces of the fetal abdomen.

Discussion

Etiology

The most common causes of meconium peritonitis are ischemic lesions of the small bowel associated with mechanical obstruction (atresia, volvulus, intussusception, congenital bands, Meckel diverticulum and internal hernia). These cases account for 50% of the cases of meconium peritonitis. Meconium peritonitis may also be caused by viral infections (cytomegalovirus, or parvovirus B19). Meconium ileus accounts for less than 25% of cases of meconium peritonitis.

Ultrasonography

The sonographic findings vary depending on several factors: the etiology, the time interval since perforation and the degree of inflammatory response. It may be seen as early as at 13 weeks of gestation. If subsequent scans are performed, the sonographic findings can track the evolution of the intra-abdominal abnormalities: initially free intraperitoneal fluid, subsequently an irregular thick-walled intra-abdominal cyst, and finally, isolated intraperitoneal calcifications.

If only a single scan is performed, the above findings may not be observed. The diagnosis of meconium peritonitis should be made if ultrasound examination demonstrates diffuse hyperechoic punctate echoes with or without acoustic shadowing in the abdominal cavity, on the hepatic surface and in the scrotal sac. If the inflammatory response remains localized a meconium pseudocyst may occur. This appears sonographically as a cystic heterogeneous mass with an irregular, calcified wall.

Meconium peritonitis should be considered in the differential diagnosis of isolated ascites with no other abnormal fluid collections that would suggest fetal hydrops.

Polyhydramnios, reported in approximately 50-60% of patients, may be caused by peristaltic deficiency associated with decreased swallowing activity.

Prognosis

Prognosis depends upon the etiology. Intraperitoneal meconium usually calcifies, sometimes within 24 hours. Bowel perforations may heal and the ascites and bowel dilatation may resolve, leaving only peritoneal calcifications as the only sonographic sign of meconium peritonitis.

Final result of the process varies and may lead to four descriptive categories of meconium peritonitis: fibro-adhesive, cystic, generalized and healed.

Eighty-six percent of fetuses with meconium peritonitis have intra-abdominal calcifications. While cystic fibrosis is universally seen in cases of meconium ileus, it is seen in only 7-40% of cases of meconium peritonitis.

References

1. Doubilet PM, Benson CB. Atlas of Ultrasound in Obstetrics and Gynecology: a multimedia reference. Lippincott Williams and Wilkins 2005;pg:130-2.
2. Foster MA, Nyberg DA, Mahony BS, Mack LA et al. Meconium peritonitis: Prenatal sonographic findings and their clinical significance. Radiology 1987;165:661-665.
3. Saleh N, Geipel A, Gembruch U, Heep A, Heydweiller A, Bartmann P, Franz AR, Müller A. Prenatal diagnosis and postnatal management of meconium peritonitis. Perinat Med 2009;37(5):535-8.