Prenatal causes of an allantoic cyst with a patent urachus

Prenatal diagnosis of an allantoic cyst with a patent urachus is rare. A urological etiology can sometimes be associated with it. We report 4 cases of allantoic cyst with a patent urachus and reviewed the literature to investigate for any etiology using the keywords “allantoic cyst” and “patent urachus”. Diagnosis of an allantoic cyst with a patent urachus was established during the first or second trimester of pregnancy. In two cases, rupture of prenatal cysts occurred and in one case, we described a prenatal vesicourethral abnormality. Surgery was performed with good results and no complications. A literature review collected 12 studies (15 fetuses) with a sex ratio of 3 boys/1 girl. The cysts ruptured in 2/3 of the cases, and in half of the cases, urinary abnormalities were found before birth (enlarged bladder, bladder prolapse). At birth, one boy had posterior urethral valve (PUV) and 4 boys had a bladder prolapse. The postoperative course was uneventful. We present our series with one case showing the etiology of a patent urachus during prenatal life. Cystoscopy seems to be valuable in the post-natal diagnosis. In the literature, we found one case of PUV. Surgery was performed with good results and no complications.


Introduction
The urachus is a thin fibrous remnant of the allantois, a canal which runs between the top of the bladder and the umbilicus.It normally closes during the second part of pregnancy.Failure of closure of this communication results in various abnormalities; one of them are cysts, which can be detected on the umbilical cord using prenatal ultrasonography 1.However, an allantoic cyst with a patent urachus is extremely rare with an incidence of 3 per 1,000,000 live births in whom males are more often affected with a sex ratio of 3 boys for 1 girl 1.We tried to identify a urological explanation to this pathology through 4 cases treated in our unit and a literature review in PubMed.

Material and Methods
A single centre review reported 4 cases of allantoic cyst with a patent urachus from 1999 to 2014.Retrospective data was collected and reviewed as follows: perinatal data, ultrasonography, clinical examination at birth, and urinary tract examination, type of surgical procedure, and outcome.Descriptive data of the 4 cases are presented, and a review of the literature was performed using the following key words: "allantoic cyst" and "patent urachus".Only studies that talked about prenatal diagnosis were selected.We excluded those talking about urachus complications during childhood and after.We were looking for data about cyst size, rupture, congenital abnormalities, neonatal morbidity and surgery.
Case 1 A 34-year-old woman, gravida 3, para 2, was referred to our unit for the first trimester sonography.At 13 weeks of gestation (WG), the fetal bladder was enlarged and associated with a 16mm ventral cyst [Fig.1].During the 18-WG evaluation, the cyst size increased to 29mm.However, the size of the bladder was normal.The cyst's size was 30mm at 22 WG with an umbilical cord edema evidenced on Doppler.At the end of the second trimester, the allantoic cyst disappeared, the bladder was empty, and arterial flow on Doppler ultrasound was normal apart from an edema of the cord.She delivered a healthy 3,050g boy at term.There was a remnant bladder-umbilical communication through the cord.Surgery was performed on the first day of life.Cystography and urethrocystoscopy revealed no bladder abnormality, no posterior urethral valve, and no vesicoureteral reflux (VUR).Nevertheless, cystoscopy revealed a marked bladder neck and a flattened veru montanum.The urachus was removed and umbilical vessels were ligated.Urethral catheter was left in place during 2 days and when removed, the boy had normal micturition.Post-natal ultrasound evaluation, 72 hours after surgery, confirmed normal kidneys, and normal bladder size one month later.One year later, micturition and urinary sonography were normal.
Case 2 A 23-year-old woman, gravida 2, para 1, had a first trimester ultrasound evaluation (16 WG).It revealed a 27mm ventral cyst and a normal bladder.It was not possible to distinguish between a vesico-allantoic cyst and bladder exstrophy.Sonography at 19, 23, and 31 WG confirmed the presence of an allantoic cyst, which increased in size and measured 27mm, 28mm, and 30mm respectively [Fig.2].Fig. 2. Allantoic cyst at 2nd trimester.
Kidneys, bladder, and other organs were normal.The karyotype confirmed a 46 XY boy without chromosomal abnormality.She delivered a baby boy weighing 3,470g at 39 WG.A bladder prolapse through the umbilicus was observed.Neonatal surgery using cystography and cystoscopy did not reveal any urinary explanation: normal bladder, and no posterior urethral valve (PUV).Excision-suture of the patent urachus was performed with success.We left urethral catheter during 4 days.Clinical and sonographic control one month and eleven months later showed normal micturition and sonography.
Case 3 A 34-year-old woman was seen for referral ultrasonography at 20 WG.A 30mm cyst could not be clearly distinguished between an allantoic cyst or an omphalocele.She delivered a healthy boy with a 60mm umbilical cord cyst far from the abdominal wall.The umbilical cord was clamped without any further exploration.One month later, this boy was referred to pediatric surgery for a urinary leakage through the umbilicus.Surgical exploration revealed a communication with the bladder and no other abnormality.An excision of the urachus and suture of the top of the bladder were performed.We didn't leave urethral catheter.Histology confirmed the presence of an urachal cyst.The patient was discharged without any complication and a normal urinary ultrasonography.Clinical control 3 months later revealed no complication.
Case 4 A 27-year-old primipara was seen for referral ultrasound evaluation at 26 WG.A 20mm allantoic cyst was described.A suspicious cord edema was noticed at birth.Ten days later, urinary leakage was suspected through the umbilicus.
Pre-operative sonography revealed no kidney complication.The umbilicus could be catheterized.It revealed a communication with the bladder, which was excised and without any argument for an obstruction.We didn't leave any urethral catheter.Ultrasonography, one month later, revealed a small symmetric renal pelvic dilatation of 4mm with regression 6 months later.Three years after surgery, sonography revealed a small bilateral pyelectasis (4 mm); the micturition was normal.

Literature review
The literature review using PubMed with the words "allantoic cyst" and "patent urachus" gathered 12 corresponding studies between 1997 and 2013 gathering only 15 patients.Among 15 cases, there were 11 male patients and 3 female patients.We did not find the information for one case.Mean maternal age was 31 years (range: 18 to 41).There were 14 singletons and one monochorionic biamniotic twin pregnancies.The diagnosis was made between 12 and 27 WG.Cysts increased in size from the first to the second trimester.Prenatal cyst rupture occurred in 2/3 of cases.Seven prenatal abnormalities were described: 4 cases of enlarged bladder and 3 cases of bladder prolapse [

Discussion
In our series, prenatal diagnosis of allantoic cyst was established during the first and the beginning of the second trimester.All our fetuses were boys.Rupture of cysts occurred before birth in half of the cases (Table 1).In only one case, we could describe signs, which were in favor of a prenatal temporary obstruction of the distal urinary tract with a marked bladder neck and flattened veru montanum.The other cases did not bring any prenatal explanation.They did not have vesicoureteral reflux or other abnormality.We suspected, in the first case, one lower urinary tract obstruction that could have disappeared during pregnancy and that could explain this particular low urinary tract aspect and allantoic cyst, consequences of a high pressure in there.We founded no explanation for the 3 other patients.
Fetal MRI helps to differentiate between a real cyst, a pseudocyst, and an abdominal wall defect 1.Pseudocysts are located in a paraxial situation.They are considered to be a result of Wharton's jelly degeneration.They are often associated with structural or chromosomal abnormalities such as trisomy 13 and 18 13.Additionally, "true" cysts preferentially lie in an axial situation between umbilical vessels and they are often related with normal fetuses.with a patent urachus do not seem to be associated with a significant risk of chromosomal abnormality when isolated.Prenatal karyotype does not appear to be useful (including the complication of the sample), except in case of uncertain diagnosis.In the reviewed studies, surgical management was the rule to prevent associated complications such as local infection, urinary infection, lithiasis or cancer.Teams often sutured umbilical vessels and excised the top of the bladder to prevent urachal cancer.Gleason et al. made a review of pediatric urachal anomaly and showed no severe risk of cancer with an extrapolated number required to treat more than 8,000 to prevent one hypothetic urachal adenocarcinoma 15.On the other hand, Galati et al. observed a spontaneous resolution with non-operative management in patients younger than 6 months with small fistula 16.Urethrocystogram and cystoscopy appeared to be essential in causal diagnosis as seen in our first case with suspected prenatal anomalies and to explore the possibility of posterior urethral valves.It seems to be important to look for urinary tract evolution (sonography) and toilet training forfeiture.Indeed, Freedman and al. showed that some children with low urinary tract obstruction were not toilet-trained after 2 years old 17.In our study, we had many patients lost to follow-up before toilet training, so we were not able to compare this parameter with literature.Sonography evolution was normal.

Conclusions
Allantoic cyst with a patent urachus is a rare pathology.Most of the time, no etiology is found but urethrocystogram and cystoscopy is often performed to look for posterior urethral valves or other urinary tract abnormality.Our study has just suspected one case of prenatal lower urinary tract obstruction with a spontaneously correction.Surgery prevents complications such as infections or degeneration.There is no distinguished structural or chromosomal anomaly, which can substantiate systematic karyotype.Surgical management during the neonatal period can be discussed.However, medical supervision seems to be an acceptable alternative.In all cases, the neonatal evolution was normal with no surgical or kidney complications.Nonetheless, it is essential to follow these patients regularly until they are toilet-trained.