Allantoic cyst of the umbilical cord detected in the first trimester with good pregnancy outcome

Introduction

Allantoic cysts of the umbilical cord are embryological remnants of either the allantois or the omphalomesenteric duct and are considered to be the result of the obstruction of the embryonic vessels or liquefaction of Wharton’s jelly [1]. These cysts are rare non-neoplastic tumours of the umbilical cord located typically towards the fetal insertion [2]. Literature dealing with the umbilical cord cyst is not very abundant, especially in the case of allantoic cysts. Here we present a case of large allantoic cyst of the umbilical cord found in the first trimester with spontaneous regression and favourable outcome.

Case report

A 24-year-old primigravid patient was referred to the tertiary perinatal centre in the 14^th week of gestation due to the ultrasound finding of an umbilical cord tumour. The results of the first trimester combined test done in the 13^th week of gestation were of low risk. The current ultrasound examination revealed fetal biometry at the 14^th week of gestation with visible body movements. The nuchal translucency measured 1.3 mm. The only ultrasound finding of the fetus was a small bilateral pyelectasis measuring 2 mm with normal renal parenchyma and urinary bladder. On the fetal side of the umbilical cord around 5 cm from the insertion ultrasound revealed an anechoic cystic mass measuring 4.8 mm in diameter located in the central part of the cord with the umbilical vessels located against the outer wall detected by colour Doppler ultrasonography (Figure 1). The rest of the umbilical cord and placentation were normal. The patient was offered an invasive prenatal diagnostic test which she refused.

Figure 1:

Ultrasound examination at the 14^th week of gestation revealing an anechoic cystic mass measuring 4.2 mm in diameter located in the central part of the cord with the umbilical vessels located against the outer wall detected by colour Doppler.

Ultrasound examination in the 18^th week of pregnancy has revealed partial regression of the cyst while complete resolution of the cyst was found at the 25^th gestational week of gestation. Spontaneous delivery occurred at term with the birth of a healthy, eutrophic, female newborn. Pathologic examination of the umbilical cord did not find any abnormalities, while urologic evaluation of the newborn confirmed a normal genitourinary tract.

Discussion

The occurrence of an umbilical cord cyst in the first trimester was investigated by a group of authors who revealed that cyst could be found in the 3.4% of the examined materials with the prevalence of 20% in a case of fetal structural or chromosomal anomalies [3]. The authors recommended that in a case of associated anomalies or high-risk prenatal screening test in the first trimester, karyotyping should be performed as the prevalence of chromosomopathy in these cases is increased [3]. On the other hand, Hannaford and co-workers found that the mean diameter of the umbilical cord cyst in the first trimester was 3±2.1 mm without significant difference in the prevalence of fetal malformations regarding the cyst occurrence [4]. They did not find an association between poor pregnancy outcomes and visible umbilical cord cysts during the first trimester which is in accordance with our case report [4].

Allantoic cysts of the umbilical cord are usually located at its free loop, distant from placental and fetal compartment, unless they represent the communication with the urinary bladder as a vesico-allantoic cyst. Umbilical cord cysts represent a group of rare ultrasound findings in the first trimester usually with good outcomes, although they can be associated with chromosomal abnormalities. One case with a smaller cyst was described at the 8^th gestational weeks with a normal fetal karyotype and a good pregnancy outcome [5].

The typical ultrasound picture of the allantoic cyst includes the separation of the umbilical cord blood vessels divided with the well-distinguished anechogenic structure in the middle part of the cord without a positive blood flow within the cyst which was shown in our case (Figure 1) [6]. Doppler sonography can be very helpful in differential diagnosis of rare umbilical cord vascular tumours such as haemangioma or angiomyxoma from rudimentary structures like an allantoic cyst or umbilical cord knots and pseudo-knots. Modern ultrasound techniques such as B-mode ultrasonography and tree- and four-dimensional ultrasound have also been shown to be beneficial in diagnosis of umbilical cord cysts [7].