Figure 4: A gangrenous portion of the mid small bowel was twisted three times upon itself.
Meconium peritonitis is not an easy prenatal diagnosis, largely because it can be caused by various bowel disorders (volvulus, atresia, stenosis) as well as by genetic (cystic fibrosis) or viral diseases. Three different forms of meconium peritonitis (cystic diffuse and fibroadhesive) make the conclusive diagnosis even more difficult and increase the number of conditions to be considered in differential diagnosis. We reported a case of meconium peritonitis associated with significant bilateral hydronephrosis which mimicking fetal ascites. Fetal ascites may be present in fetuses with obstructive uropathy due to transudation of the urine across the fetal bladder or actual rupture of the fetal bladder, ureter or kidney15. Adzick et al16 observed some degree of urinary extravasation in 12 out of 44 fetuses with urinary tract obstruction. Urinary extravasation can be diffuse (urinary ascites) or localized (perirenal urinoma).
Fetal urinary ascites is associated with improved neonatal outcome because it ameliorates the degree of renal dysplasia by decompressing the high-pressure obstructed urinary tract16. In 50% of fetuses, the site of urinary extravasation causing ascites could not be determined postnatally. Isolated perirenal urinomas, on the other hand, were associated with renal dysplasia in each case. None of these fetuses had urinary ascites or prune belly17.
Meconium peritonitis is a sterile chemical peritonitis resulting from spillage of small bowel contents due to its perforation. Initial bowel pathology usually includes volvulus with or without malrotation, bowel atresia, and meconium ileus. Bowel distention may lead to compression and necrosis of the intestinal wall, resulting in vascular ischemia. Bowel is particularly prone to ischemia because of blood redistribution with preferential supply to brain and heart and decreased flow to mesentery and kidneys.
A primary vascular compromise (e.g. arterial embolism) with secondary changes in the bowel can not be ruled out as an etiological factor in these cases7. Vascular accidents had been reported to occur in 25% of cases of bowel atresia8.
Meconium peritonitis had been diagnosed prenatally in conjunction with various fetal abnormalities and diseases: small bowel perforation due to stenosis, atresia, or volvulus as well as cystic fibrosis, and viral infections. Meconium ileus due to cystic fibrosis has been identified in 15%-40% of infants with meconium peritonitis2-4. A case of meconium peritonitis in a child5 homozygous for the DF508 diagnostic of cystic fibrosis has been reported recently.
Prenatal sonographic findings which support the diagnosis of meconium peritonitis include intra-abdominal calcifications, isolated ascites, bowel dilatation, and polyhydramnios. Foster et al6 reported the incidence of these sonographic signs in seven cases of meconium peritonitis: intra-abdominal calcifications were seen in 86%, ascites in 64%, polyhydramnios in 71%, and signs of bowel obstruction in 46%
Three major forms of meconium peritonitis which can be identified on prenatal ultrasound are:
- cystic (meconium pseudocyst),
- diffuse and
Meconium pseudocyst is the most common sonographic presentation of meconium peritonitis and appears as a hyperechoic mass with well-defined rim. Ascites is also commonly seen in this form. Diffuse meconium peritonitis is usually associated with polyhydramnios, fetal ascites, and numerous intra-abdominal calcifications. The fetal abdominal wall may also appear thickened due to edema. The fibroadhesive form of meconium peritonitis results from massive deposition of calcium along the peritoneum that can eventually seal off the bowel lesion.
Differential prenatal diagnosis of meconium peritonitis is reflected in Table 1. The most common condition to be considered for differential diagnosis is nonimmune hydrops. The presence of pleural and/or pericardial effusions, skin edema and placentomegaly are common in nonimmune hydrops and not typical for meconium peritonitis.
Cloacal anomalies are characterized by a large cystic structure in the fetal pelvis and abdomen10. Megacytis-microcolon syndrome is associated with bilateral hydronephrosis and massively dilated fetal bladder17,18. Ascites is usually present.
Meconium peritonitis is associated with small bowel disorders in approximately 50% of cases. Most common bowel pathologies are volvulus, atresia, meconium ileus, intussusception, internal hernias, congenital bands and perforation of Meckel diverticulum. Cystic fibrosis had been diagnosed in 15-40% of these cases6.
If diagnosis is made prior to fetal viability, the possibility of cystic fibrosis should be ruled out. If a fetus tests positive for cystic fibrosis, the option of pregnancy termination can be discussed. Serial ultrasound examinations are indicated to assess the degree of ascites. In case of rapid worsening of ascites, preterm delivery can be recommended to avoid further damage to the bowel11. Cesarean section had not proven to improve neonatal outcome in these cases and there fore is not recommended on an elective basis. An inutero paracentesis had been suggested in cases of severe abdominal distention prior to elective induction of labor12. Fetuses with meconium peritonitis should be delivered in tertiary care centers where pediatric surgery services are available.
In conclusion, the possibility of meconium peritonitis should be considered when ascites is detected in fetuses with bilateral hydronephrosis. Increased intra-abdominal pressure can, in some cases, cause transient ureteral obstruction and secondary hydronephrosis. Postnatal disappearance of kidney changes can rule out intrinsic renal pathology.
1. Forouhar F. Meconium peritonitis: Pathology, evolution and diagnosis. Am J Clin Pathol 78:208-213, 1982.
2. Lorimer WS, Ellis DG. Meconium peritonitis. Surgery 60:470-475, 1966.
3. Payne RM, Nielsen AM. Meconium peritonitis. Am Surg 28:224-231, 1983.
4. Park RW, Grand RJ. Gastrointestinal mainifestations of cystic fibrosis: A review. Gastroenterology 81:1143-1161, 1981.
5. Catanzarite V, Wozniak P, Maida C, Mascarello J, Senae M. Meconium peritonitis. Fetus 3:4, 1993.
6. Foster MA, Nyberg DA, Mahony BS, et al. Meconium peritonitis: Prenatal sonographic findings and clinical significance. Radiology 165:661-665, 1987.
7. Petrikovsky BM, Nochimson DJ, Campbell WA, et al. Fetal jejunoileal atresia with persistent omphalomesenteric duct. Am J Obstet Gynecol 158:173-5, 1988.
8. Delorimier A, Fonkalseud E, Hays D. Congenital atresia of the jejunum and the ileum. Surgery 65:819, 1969.
9. Pletcher BA, Williams MK, Mulivor R, et al. Intrauterine cytomegalovirus infection presenting as fetal meconium peritonitis. Obstet Gynecol 78:903-905, 1991.
10. Petrikovsky BM, Walzak MP, D"Addario PF. Fetal cloacal anomalies: Prenatal sonographic findings and differential diagnosis. Obstet Gynecol 72:464-9, 1988.
11. Romero R, Pilu G, J, Jeanty P, et al (Ed). Meconium Peritonitis in Prenatal Diagnosis of Congenital Anomalies. Appleton & Lange, Norwalk, p 243-5, 1986.
12. Baxi LV, Yeh MN, Blanc WA, et al. Antepartum diagnosis and management of in utero intestinal volvulus with perforation. N Engl J Med 308:25, 1983.
13. Dillard JP, Edwards DU, Leopold GR: Meconium peritonitis masquerading as fetal hydrops. J Ultrasound Med 6:49-51, 1987.
14. Kenney PJ, Spirt BA, Ellis DA, Patil U. Scrotal masses caused by meconium peritonitis: prenatal sonographic diagnosis. Radiology 154:362,1985.
15. Crane JP. Anomalies of the renal system. In Ultrasound in Obstetrics and Gynecology. F. Chervenak, G. Isaacson, S. Campbell (Ed). Little Brown & Co, Boston,. 1993, Volume 2, p 467-480.
16. Adzick NS, Harrison MR, Flake AW, et al. Urinary extravasation in the fetus with obstructive uropathy. J Pediatr Sug 20:608, 1985.
17. Vintzileos AM, Eisenfeld LI, Herson BC, et al: Megacystics-microcolon-intestinal hypoperistalsis syndrome. Prenatal sonographic findings and review of the literature. Am J Perinatol 3:297, 1986.
18. Young LW, Yunis EJ, Girdany BR, et al: Megacystic microcolon-intestinal hypoperistalsis syndrome: Additional clinical, radiologic, surgical, and histopathologic aspects. AJR 137:749, 1981.