Meconium Pseudocyst

Rare cases of meconium peritonitis will be associated with a meconium pseudocyst, which consists of dilated meconium-filled intestine with a smooth muscle layer connecting the cyst to the normal intestine, but without an epithelial layer due to inflammation. This should be differentiated from cystic-type meconium peritonitis, in which the inflammatory reaction to the extruded meconium leads to formation of an intraperitoneal cystic cavity with a fibrous wall around the extravasated intestinal contents.¹

P78.0: perinatal intestinal perforation, including meconium peritonitis.

P75*:  meconium ileus in the setting of cystic fibrosis.

A true meconium pseudocyst is a rare condition, with approximately 8 cases reported in the literature between 1996 and 2012.^1–7

During pregnancy, the fetus begins to swallow amniotic fluid and secrete bile at approximately 12 weeks’ gestational age. Meconium reaches the ileum by 16 weeks’ gestational age, and bowel peristalsis begins by 20 weeks’ gestational age.^8,9 Primary or secondary fetal intestinal obstruction after this time results in hyperperistalsis, thinning of the intestinal wall, and may result in perforation, typically involving the small bowel. As a result, meconium and digestive enzymes, including pancreatic trypsin, spill into the peritoneal cavity, where they produce a chemical peritonitis.⁸ The severe intraperitoneal inflammatory reaction due to this chemical peritonitis may lead to organization of a fibrous wall around the extravasated intestinal contents which effectively localizes the peritoneal reaction, and is termed cystic-type meconium peritonitis^10,11 (See VISUOG chapter on Meconium Peritonitis).

In contrast, prenatal volvulus or marked segmental dilatation proximal to a site of intestinal obstruction may cause loss of the mucosal epithelium due to mucosal necrosis or exposure to the inflammatory milieu following intestinal perforation, and result in continued dilatation of the weakened intestinal wall. This process results in an agglutinated mass between atretic or stenotic small bowel segments, which is called a meconium pseudocyst.¹⁰

It is thought that meconium pseudocysts arise as a result of three events: 1) intestinal dilatation proximal to atresia; 2) mechanical disruption of intestinal vascular supply (e.g. volvulus, intussusception) leading to mucosal, submucosal, or transmural necrosis and secondary intestinal wall weakness; and 3) inflammation following intestinal perforation causing obstruction.¹

Meconium peritonitis has been categorized into three pathologic variants: 1) the fibroadhesive type, 2) the cystic type, and 3) the generalized type.¹¹ In the fibroadhesive type, the sterile chemical peritonitis induces a fibroblastic reaction, which may effectively seal off the perforation and limit further extravasation of meconium into the peritoneal cavity. If the intestinal perforation is not effectively sealed off, the fibroblastic reaction will lead to an agglutination of intraperitoneal contents around the spilled meconium and fibrous deposition, thereby walling off the intraperitoneal meconium and forming a cystic appearance. This may further increasing in size with additional meconium extravasation. In the generalized type, intestinal perforation occurs in the peri-neonatal period, resulting in recently-deposited fibrinous adhesions diffusely throughout the peritoneal cavity rather than a localized mature fibrous cyst wall.¹¹

In contrast, meconium pseudocyst occurs due to thinning and subsequent dilatation of the intestinal wall proximal to the site of obstruction, likely due to a vascular disruption. As a result, the pseudocyst maintains a smooth muscle sheath continuous with the normal intestine, but lacks an intestinal epithelial layer due to mucosal necrosis and exposure to inflammation by digestive enzymes.¹ The rupture site on a pathology specimen demonstrates an isolated discontinuity of the muscle layers which is replaced by fibrous tissue.⁴

Polyhydramnios often accompanies meconium peritonitis and meconium pseudocysts, and is thought to be due to either extraluminal mass-effect or from proximal blockage of the intestines as is seen with jejunal atresia (See VISUOG chapter on Jejunal and Ileal atresias).

When the pseudocysts are large, mass-effect may additionally cause compression of the lungs. Occasionally, fetal hydrops or circulatory failure is seen.¹²

No studies have evaluated the recurrence risk for meconium peritonitis or meconium pseudocyst in the setting of prior meconium pseudocyst.

Meconium pseudocysts present sonographically in a variety of ways. They can present as a hyperechoic intraabdominal cystic mass with a thick, well-circumscribed, echogenic wall with echogenic viscous contents and peripheral focal calcifications.¹⁴ Some have mixed echogenicity with fluid/fluid levels.³  Others may present as a thin-walled, hypoechoic cystic abdominal masses without septations or solid components.⁶ Most have calcifications in the wall, however, these are not necessary.^3,6 These masses may present only in the third trimester after prior normal ultrasound examinations.³ The mass may be large.¹⁵

Additional findings commonly seen include: intraabdominal calcifications on the surface of the peritoneum and/or bowel, ascites, dilated bowel loops with peristalsis and polyhydramnios. These findings are commonly seen in cases of meconium peritonitis. Intraabdominal calcifications may be absent or identified only on subsequent scans.^3,4,16 Occasionally, fetuses with meconium pseudocyst may develop generalized hydrops.¹⁵

Fetal MRI may be considered as an adjunctive study when evaluating a fetal intra-abdominal cyst; however, findings in meconium pseudocysts are highly variable. Wong et al suggested that the MRI diagnostic criteria of a meconium pseudocyst should include: 1) the presence of internal septa; 2) variable signal intensity depending on the age of the cyst, the size, and the patency of the bowel perforation, and whether the meconium is normally produced; 3) proximal bowel dilation; 4) an absence or reduction of material showing a high T1 signal in the distal colon; and 5) no restriction of water diffusion on diffusion-weighted images.⁷ However, these criteria have been considered by some to be much more specific than they are sensitive for the diagnosis of meconium pseudocyst.¹⁷

The differential diagnosis for meconium pseudocyst includes any type of intraabdominal cyst, including: intestinal duplication cyst, neuroblastoma, Wilm’s tumor, gastric or sacrococcygeal teratoma, hepatoblastoma, adrenal haemorrhage, adrenal cysts, mesenteric cysts, haemorrhagic ovarian cysts, Meckel’s diverticulum, renal cysts, obstructive uropathy, urachal cysts, choledochal cysts, pancreatic cysts, splenic cysts, and fetus-in-fetu.^{3,6,10,17,19–22} Differentiating among these cystic intraabdominal masses should be done by assessing the location, sonographic appearance, gestational age at diagnosis, and natural history of the mass. About 15% of these intraabdominal masses are of gastrointestinal origin, with the majority of these being duplications.²³

Gastrointestinal duplication cysts, meconium pseudocyst, cystic-type meconium peritonitis, and segmental dilatation of the small bowel may appear sonographically similar. Since neonatal management strategies are markedly different, neonatal CT may be necessary to guide management.¹

If a meconium pseudocyst is suspected, a thorough search for additional abnormalities is suggested, with particular attention to the fetal abdomen, anus and intraabdominal structures. The fetus should be assessed for findings associated with meconium peritonitis including ascites, intraabdominal calcifications, bowel obstruction and polyhydramnios.

If intraabdominal calcifications are identified, evaluation for viral infections including cytomegalovirus (CMV), herpes, parvovirus, rubella and other viruses can be considered.

The absence of sonographically visualized intraperitoneal calcifications in meconium peritonitis disorders favors cystic fibrosis as the underlying etiology, as normal pancreatic enzymes facilitate precipitation of calcium salts.⁸ The latest case series and systematic review demonstrated that 60% of patients with meconium peritonitis who had cystic fibrosis had intraperitoneal calcifications, while 100% of those without cystic fibrosis had intraperitoneal calcifications.^8,25–28

Of the 8 reported cases of true meconium pseudocysts between 1996 and 2012, only 2 report results of cystic fibrosis testing, both of which were negative.^1–7 However, given the limited literature, it is reasonable to rule out cystic fibrosis in cases where meconium pseudocyst is suspected, especially if there is a clinical suspicion of meconium ileus as an underlying cause. ^19,24 This can be done with amniocentesis or with newborn testing.

Sonographic monitoring of with weekly ultrasound scans and twice weekly biophysical profiles in the third trimester has been recommended to assess fetal growth and development of any associated complications, including bowel obstruction, fetal ascites, polyhydramnios, or changes in the meconium pseudocyst.²⁹ The size and appearance of the fetal mass should be re-evaluated at each visit to ensure that the mass remains consistent with the diagnosis of a meconium pseudocyst.

There are case reports describing the antenatal rupture of a meconium pseudocyst, with sonographic disappearance of a previously-identified cystic mass, new-onset or worsening fetal ascites, and rapid bowel dilatation.¹⁷

If mass-effect from meconium pseudocyst, giant cystic-type meconium peritonitis, or fetal ascites leads to diaphragmatic compression and cardiovascular compromise, percutaneous abdominal drainage may be considered prior to delivery.²⁹ This may lead to meconium-staining of the amniotic fluid.³ Occasionally, ascites may be hemorrhagic, so monitoring with middle cerebral artery peak systolic velocities is suggested (See VISUOG chapter on Meconium Peritonitis).

There are case reports describing the antenatal rupture of a meconium pseudocyst, with sonographic disappearance of a previously-identified cystic mass, new-onset or worsening fetal ascites, and rapid bowel dilatation.¹⁷

Meconium peritonitis is associated with a 20% to 30% incidence of prematurity, with the highest association of preterm labor among those complicated by meconium pseudocysts, so the patient should be alerted to present for complaints of increased uterine activity.^13,24 Steroids to enhance pulmonary maturity are indicated if there is a concern for preterm delivery.

Prenatal diagnosis should prompt consideration of prenatal consultation with Neonatology and Pediatric Surgery. Delivery in a tertiary care setting where Pediatric Radiology consultation is available is suggested.

Delivery can be vaginal with Caesarean delivery reserved for the usual obstetric indications or for cases where abdominal dystocia is anticipated.

After delivery, abdominal examination, a plain abdominal radiograph, and an abdominal ultrasound are commonly performed to confirm prenatal findings. An upper GI study and a small bowel follow-through may also be considered.³⁰

On abdominal radiographs, 85% of meconium pseudocysts demonstrate punctate calcifications of the cyst wall, and 66% demonstrate air within the cyst.¹ “Eggshell” calcifications, referring to a well-defined rim of calcification along the circumference of a cystic structure, are caused by a chemical reaction of pancreatic enzymes within the extravasated meconium, and are thought to be a pathognomonic finding for meconium pseudocyst or cystic-type meconium peritonitis, and less common in neonates with cystic fibrosis due to pancreatic insufficiency.¹⁶ Neonatal computed tomography may be obtained to further elucidate the origin of an undifferentiated intra-abdominal cyst, and, in the case of a meconium pseudocyst, may demonstrate a well-defined calcified cyst wall, air within the cyst, and obvious communication between the cyst and the proximal dilated intestine.¹

Prenatally undetected cases of meconium pseudocyst or giant cystic-type meconium peritonitis present with the classic clinical triad of: 1) severe abdominal distention, 2) bilious vomiting, and 3) failure to pass meconium in the first day of life. This triad, especially when coupled with an obstetrical history of abdominal dystocia should raise clinical suspicion for a neonatal disorder in the meconium peritonitis spectrum.¹⁸

Cystic-type meconium peritonitis typically requires immediate surgical intervention with cyst drainage and enterostomy with subsequent elective reanastomosis, as the cyst wall may be too frail to resect at time of the initial operation.³¹ In patients with meconium pseudocyst, the cyst wall may be firm enough to resect due to the preserved smooth muscle layer, so a 1-stage resection with a primary anastomosis may be performed within 24 hours of delivery.⁴ The purpose of surgical intervention is to re-establish intestinal continuity, preserve bowel length, and correct the underlying pathologic process.⁴ Antibiotics should be started pre-operatively and continued postoperatively.¹⁸ The postoperative course may be complicated by adhesions which may cause recurrent obstruction.³²

Due to improvements in antenatal diagnosis, neonatal intensive care, and postoperative management, mortality in meconium peritonitis has decreased from 50% to 11%.³⁰ With appropriate early surgical intervention, survival of infants with meconium pseudocyst or giant cystic-type meconium peritonitis should approach that of neonates with meconium peritonitis without pseudocyst or giant cystic-type meconium peritonitis.¹⁸ An inappropriate delay in surgical intervention allows passage of intestinal microflora from the early colonized postnatal gut into the previously sterile meconium pseudocyst, which may convert an aseptic peritonitis into a septic peritonitis.¹⁸

^{1.      Minato M, Okada T, Miyagi H, et al. Meconium pseudocyst with particular pathologic findings: A case report and review of the literature. J Pediatr Surg. 2012. doi:10.1016/j.jpedsurg.2011.11.050}

^{2.      Douglas D. Meconium pseudocyst. Pediatr Radiol. 2010. doi:10.1007/s00247-010-1748-x}

^{3.      Valladares E, Rodriguez D, Vela A, Cabre S, Lailla JM. Meconium pseudocyst secondary to ileum volvulus perforation without peritoneal calcification: A case report. J Med Case Rep. 2010. doi:10.1186/1752-1947-4-292}

^{4.      Lee YC, Chen CJ. Meconium pseudocyst: A classical and successfully treated case. J Formos Med Assoc. 2009. doi:10.1016/S0929-6646(09)60059-0}

^{5.      Larson SD, Hebra A. Meconium Pseudocyst in a Newborn. J Am Coll Surg. 2006. doi:10.1016/j.jamcollsurg.2006.02.037}

^{6.      Simonovsky V, Lisy J. Meconium pseudocyst secondary to ileal atresia complicated by volvulus: antenatal MR demonstration. Pediatr Radiol. 2007.}

^{7.      Wong AM, Toh CH, Lien R, Chao AS, Wong HF, Ng KK. Prenatal MR imaging of a meconium pseudocyst extending to the right subphrenic space with right lung compression. Pediatr Radiol. 2006. doi:10.1007/s00247-006-0294-z}

^{8.      Finkel LI, Slovis TL. Meconium peritonitis, intraperitoneal calcifications and cystic fibrosis. Pediatr Radiol. 1982. doi:10.1007/BF00972441}

^{9.      Forouhar F. Meconium peritonitis. Pathology, evolution, and diagnosis. Am J Clin Pathol. 1982. doi:10.1093/ajcp/78.2.208}

^{10.    Effmann EL, Griscom NT, Colodny AH, Vawter GF. Neonatal gastrointestinal masses arising late in gestation. Am J Roentgenol. 1980. doi:10.2214/ajr.135.4.681}

^{11.    Lorimer WS, Ellis DG. Meconium peritonitis. Surgery. 1966. doi:10.5555/uri:pii:0039606066902108}

^{12.    Olnick HM, Hatcher MB. Meconium peritonitis. J Am Med Assoc. 1953. doi:10.1001/jama.1953.03690070016005}

^{13.    Catania VD, Briganti V, Di Giacomo V, et al. Fetal intra-abdominal cysts: Accuracy and predictive value of prenatal ultrasound. J Matern Neonatal Med. 2016. doi:10.3109/14767058.2015.1059812}

^{14.    Foster MA, Nyberg DA, Mahony BS, Mack LA, Marks WM, Raabe RD. Meconium peritonitis: Prenatal sonographic findings and their clinical significance. Radiology. 1987. doi:10.1148/radiology.165.3.3317498}

^{15.    Eckoldt F, Heiling KS, Woderich R, Kraft S, et al. Meconium peritonitis and pseudo-cyst formation: prenatal diagnosis and post-natal course. Prenat Diagn 2003;23:904-908.}

^{16.    Ascherl R, Vaz Pimentel D, Knüpfer M, Sorge I, Lacher M, Zimmermann P. Image of the Month: Meconium Peritonitis with Pseudocyst—A Spot Diagnosis in Newborns. Eur J Pediatr Surg Reports. 2020. doi:10.1055/s-0039-3399556}

^{17.    Nakajima Y, Masaoka N, Asanuma A, et al. A large meconium pseudocyst that developed into the generalized type during the antepartum period. J Med Ultrason. 2011. doi:10.1007/s10396-010-0281-8}

^{18.    Careskey JM, Grosfeld JL, Weber TR, Malangoni MA. Giant cystic meconium peritonitis (GCMP): Improved management based on clinical and laboratory observations. J Pediatr Surg. 1982. doi:10.1016/S0022-3468(82)80094-8}

^{19.    Reynolds E, Douglass B, Bleacher J. Meconium peritonitis. J Perinatol. 2000. doi:10.1038/sj.jp.7200287}

^{20.    McEwing R, Hayward C, Furness M. Foetal cystic abdominal masses. Australas Radiol. 2003. doi:10.1046/j.0004-8461.2003.01136.x}

^{21.    Khong PL, Cheung SWC, Leong LLY, Ooi CGC. Ultrasonography on intra-abdominal cystic lesions in the newborn. Clin Radiol. 2003. doi:10.1016/S0009-9260(03)00125-9}

^{22.    Khadaroo RG, Evans MG, Honore LH, Bhargava R, Phillipos E. Fetus-in-fetu presenting as cystic meconium peritonitis: Diagnosis, pathology, and surgical management. J Pediatr Surg. 2000. doi:10.1053/jpsu.2000.6037}

^{23.    Griscom NT. The roentgenology of neonatal abdominal masses. Am J Roentgenol Radium Ther Nucl Med. 1965.}

^{24.    Kalayoglu M, Sieber WK, Rodnan JB, Kiesewetter WB. Meconium ileus: A critical review of treatment and eventual prognosis. J Pediatr Surg. 1971. doi:10.1016/0022-3468(71)90470-2}

^{25.    Grossman H, Berdon WE, Baker DH. Gastrointestinal findings in cystic fibrosis. Am J Roentgenol Radium Ther Nucl Med. 1966. doi:10.2214/ajr.97.1.227}

^{26.    Leonidas JC, Berdon WE, Baker DH, Santulli T V. Meconium ileus and its complications. A reappraisal of plain film roentgen diagnostic criteria. Am J Roentgenol Radium Ther Nucl Med. 1970. doi:10.2214/ajr.108.3.598}

^{27.    Donnison AB, Shwachman H, Gross RE. A review of 164 children with meconium ileus seen at the Children’s Hospital Medical Center, Boston. Pediatrics. 1966.}

^{28.    Holsclaw DS, Eckstein HB, Nixon HH. Meconium Ileus: A 20-Year Review of 109 Cases. Am J Dis Child. 1965. doi:10.1001/archpedi.1965.02090020103003}

^{29.    Konje JC, de Chazal R, MacFadyen U, Taylor DJ. Antenatal diagnosis and management of meconium peritonitis: a case report and review of the literature. Ultrasound Obstet Gynecol. 1995. doi:10.1046/j.1469-0705.1995.06010066.x}

^{30.    Dirkes K, Crombleholme TM, Craigo SD, et al. The natural history of meconium peritonitis diagnosed in utero. J Pediatr Surg. 1995. doi:10.1016/0022-3468(95)90325-9}

^{31.    Tanaka K, Hashizume K, Kawarasaki H, Iwanaka T, Tsuchida Y. Elective surgery for cystic meconium peritonitis: Report of two cases. J Pediatr Surg. 1993.}

^{32.    Conrad HA, Robbins FR. Congenital atresia of the jejunum with meconium peritonitis. J Int Coll Surg. 1951.}

Please note that the maximum upload size is 5MB, and larger images and video clips can be sent to [email protected].