Maternal Fetal Medicine, San Diego Perinatal Center. 7910 Frost Street Suite 140,  San Diego California 92123 USA, and Sharp Mary Birch Hospital for Women and Newborns, 3003 Health Center Drive, San Diego California 92123 USA. 
Address correspondence to Val Catanzarite MD PhD, Chief, Division of  Maternal Fetal Medicine, San Diego Perinatal Center. 7910 Frost Street Suite 140,  San Diego California 92123 US (vcatanza@gmail.com)

Synonyms

Umbilical cord cyst, allantoic cyst, patent urachus, umbilical cord pseudocyst, umbilical cord edema

Definition

Allantoic cyst of the umbilical cord is a rare anomaly in which a patent urachus links the bladder to a true cyst of the umbilical cord  (1).

Case report

A 31-year-old (G2P1) was referred to our Prenatal Diagnostic Center at 21 weeks gestation because of a suspected umbilical cord cyst. Medical and family history, and the course of the pregnancy had been unremarkable. 

The initial sonogram demonstrated a 3 cm, unilocular cyst within the cord, within 1 cm of the umbilicus. The ventral wall was intact. Echo texture within the cyst was uniform and similar to that of amniotic fluid. The umbilical vessels were noted to splay around the cyst. Three dimensional rendered images showed a smooth cyst of the cord. (Figures 1a-d).

Figures 1a, 1b - 3d rendered image of the umbilical cord cyst.

Figure 1 c - Intact ventral wall.

Figures 1 d, 1 e - Umbilical vessels splay around cyst. The urachus could not be demonstrated, either within the fetal abdomen or at the umbilicus. No fetal anomalies were appreciated, and the fetal kidneys and bladder appeared normal.

The presumptive diagnosis of allantoic cyst of the cord was made. A repeat sonogram showed the cyst to increase in size to 4.8 cm in diameter at 26 weeks.

Figure 2 - Gestational age 26 wks: 4.8 cm diameter. Note cord edema (yellow arrow).

Serial sonograms showed normal fetal growth, fluid, and umbilical cord Doppler studies, but cord edema developed at 30 weeks gestation. Twice weekly fetal monitoring and amniotic fluid assessments were reassuring. On the final sonogram at 36.5 weeks, cord edema and multiple small irregularly shaped cysts within the cord were present.

Figures 3 a, b, c: Umbilical cord at 36.5 weeks. Cross sections through the cord showing vessels splaying around a central cyst and more peripheral pseudocyst; figure b shows stromal edema and pseudocyst; figure c shows cord edema and multiple pseudocysts. 

The baby delivered vaginally a week later and did prove to have a patent urachus, with no other abnormalities, and underwent uneventful surgery for patent urachus. Pathologic examination of the cord confirmed both a true cyst, and “massive edema”.

History 

The first report of patent urachus was attributed Bartholomaeus Cabrolius in 1550 (1). Begg was able to collect 58 cases from the literature in a review in 1927, and Bilchert and Nielsen found another 92 reports from 1927 to 1971 (4). The anomalies most commonly associated with patent urachus are bladder outlet obstruction,  urachal cysts, and other anomalies of urinary tract. A patent urachus can also cause both  cysts and pseudocysts of the umbilical cord.

Prevalence

Patent urachus is rare, with frequency quoted as 1-2.5 per 100,000 live births (2). The prevalence of allantoic cysts of the cord is not know with certainty but is likely similar.

Etiology

The etiology of patent urachus is unknown; it may be associated with other abnormalities of the urinary tract.

Pathogenesis

Allantoic cysts occurs due to failure of atresia of the vesiculoallantoic remnant in the formation of the urachus. Normally, the urachus courses from the bladder dome, within the parietal peritoneum of the abdominal wall, and through the umbilicus,  terminating in the base of the cord. With failure of  atresia, there can be communication between the bladder the allantoic remnant withithin the cord. Urine flow through the urachus into the cyst can cause expansion in size. Bladder outlet obstruction may predispose to the development of allantoic cysts. 

Sonographic findings

First trimester megacystis, visible communication between the dome of the bladder and a cyst within the umbilical cord, and cord cysts and pseudocysts can be seen in patent urachus with an allantoic cyst of the cord.. 

Implications for targeted examinations

Prenatal sonographic diagnosis of vesiculoallantoic or allantoic cysts of the cord was first reported by Sachs (4) in 1982, and there have been over 20  subsequent reports (5-19, 23-28, 30-34)) of patent urachus with  allantoic cysts of the cord, some in association with  cord pseudocysts and/or and cord edema. The typical sonographic findings of allantoic cysts are cord cysts in proximity to the umbilicus, an intact ventral wall, splaying of the umbilical vessels around the cyst, and in some cases direct demonstration of urine flow from the bladder to the cyst and back, via the patent urachus. 

Differential diagnosis

Cystic spaces are visible within the umbilical cord in 2% of early pregnancies. These clear spaces may represent true cysts, which have an epithelial lining, or pseudocysts, which do not (20). Umbilical cord cysts carry an important  association with fetal abnormalities, including chromosomal aneuploidy (22,23). The work of  Ghezzi (23 ) and Gilboa (29) suggests  that the risk is much lower with an isolated single first trimester cyst that resolves later in pregnancy, and higher with multiple cysts. The frequency of umbilical cord cysts is lower in the second and third trimesters.

When an umbilical cord cyst close to the ventral wall of the fetus is suspected on prenatal sonography, color Doppler studies can exclude vascular malformations of the cord, and a comprehensive  anatomic survey should be performed to search for associated fetal abnormalities, and to differentiate cord cyst from abdominal wall defects such as omphalocele. 

Associated anomalies

If an allantoic cyst is present, potential associations with other malformations of the fetus, particularly urinary tract malformations, must be borne in mind. Associated urinary tract malformations  include posterior urethral valves (30) and bladder prolapse into the cyst (e.g., 24, 31), and Sepulveda and colleagues have reported first trimester megacystic (which may subsequently resolve) as an early sonographic finding in cases subsequently found to have patent urachus.  There has been one reported case in which the fetus proved to have trisomy 21 (12), and one in with a coexistent omphalocele (5).

Prognosis

There have been reports of cord complications in pregnancies with patent urachus (see below). For liveborn infants without associated anomalies, the postnatal surgical repair is straightforward and outcomes are excellent. 

Recurrence risk

Patent urachus has not been reported to recur in subsequent pregnancies. 

Management

Allantoic cysts can increase in size during  pregnancy, and fetal compromise due to compression of cord vessels by the cyst (9) and fetal demise with thrombosis of cord vessels (30) have been reported. It seems prudent to recommend serial sonograms to assess fetal growth and appearance of the cyst in the second trimester, and serial Doppler studies and antenatal fetal monitoring during the third trimester, as was performed for the case reported here. 

An unexpected finding in the case reported here case was the development of edema and additional clear spaces (pseudocysts) with the cord in the late third trimester. From prior publications, it is known that patent urachus is associated not only allantoic cysts, but also with cord pseudocysts and cord edema. The mechanism of pseudocyst formation remains speculative (14, 17, 18, 20). The case presented here illustrates all three sonographic findings and demonstrates that the three can occur together.

In the past, the diagnosis of patent urachus was triggered by urinary drainage from the umbilical cord stump within the first weeks of life. For cases with allantoic cyst suspected based on prenatal imaging, recommendations include surgical consultation  during the third trimester of pregnancy, clamping of the cord distal to the cyst, and postnatal  radiologic and clinical evaluation for patent urachus and for associated fetal malformations.

References

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3. Bilchert M, Nielsen OV: Congenital patent urachus and acquired variants. Acta Chir Scand 1971; 137: 807-814
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