1 Diagnostico Maipu, Buenos Aires, Argentina
2 Hospital Italiano de Buenos Aires,  Argentina

Incidence: 0.6: 10.000 female births

Etiology 
Hydrometrocolpos are in most cases sporadic (1)
In McKusic-Kaufman syndrome, hydrometrocolpos is due to either cervical or vaginal atresia and not to an urogenital sinus(1).
Hydrometrocolpos following prenatal dexamethasone treatment for congenital adrenal hyperplasia has also been described (2,3).
It has also been associated with ambiguous genitalia in 45,X/46,XY mosaicism (4).

Case report

In this case, prenatal images show a hydrometrocolpos (distended vagina a bicornuate uterus by urine) caused by the vaginal obstruction and the reflux of urine. The case is an urogenital sinus with the uretra going into the anterior aspect of the vagina. It was an hydrocolpos (actually urine not hydro) and a bicornuate uterus (hydrometrocolpos).
Other forms of vaginal obstruction are caused by vaginal or cervical atresia, high-grade stenosis, a transverse septum, an imperforate membrane or cloacal malformation (5-7).

Of course this fetus has a sliver of ascites around the bladder (the larger cystic mass in the middle of the screen). The two little "rabbit ears†on top of the bladder represents the 2 horns of a bicornuate uterus.

The sonographig findings:
Fluid-filled midline mass, behind the bladder and anterior to the spine, surrounded by the umbilical arteries. It is important to wait until a little amount of urine fills the bladder to make differential diagnosis with megacystis.
The top of the image may show the distended uterus (with thicker walls than the bladder) and the dilated Fallopian tubes.
The fluid inside the images usually contains small echoes that represent uterus secretion (mother hormonal stimulation) or blood (1,5,7,8).

Differential Diagnosis

• Megacystis.
• Ovarian cyst: not usually in the midline, not tubular and without the irregular shape in the wall because of the presence of the uterus and tubes.
• Mesenteric cyst, anterior meningoceles, and other sacral tumors (9).

Associated Anomalies:  it has been associated to uterus anomalies (bicornuate, cervical atresia), vaginal atresia or duplication; hydronephrosis, kidney agenesia, imperforate anus, polycystic kidneys, esophageal atresia and sacral hypoplasia (10,15)

Obstetrical Management: Not altered

Prognosis
Vaginal catheterization for hydrometrocolpos and surgical correction is use, with good results (11,12).

References

1) Romero R, Pilu Gianluigi, Jeanty P. Ghidini Alessandro, Hobbins  John C. The Genital tract. 1987 p: 301-310.

2) Couper JJ, Hutsson JM, Warne GL. Hydrometrocolpos following prenatal dexamethasone treatment for congenital hyperplasia (21 — hydroxilase deficiency). Eur J pediatr. 1993 Jan; 152(1):9-11.

3)Moore Keith L. The Urogenital System in The Developing Human, 1988. p 246-84.

4)Wheeler M, Peakman D, Robinson A, Henry G. 45,X/46,XY mosaicism: contrast of prenatal and postnatal diagnosis. Am J Med Genet. 1988 Mar:29(3):565-71.

5)Siegel Marilyn J. Female Pelvis in Pediatric sonography 1995 p : 437-78.

6)Blask AR, Sanders RC, Gearhart JP. Obstructed uterovaginal anomalies: anomalies: demonstration with sonography. Part I. Neonates and infants.

7)Paltiel Harriet j. Neonatal Hydrocolpos in Fetal & Pediatric Ultrasound 2001 p.476-9.

8)Geifman-holtzman o, Crane SS, Winderl L, Holmes M. Persistent Urogenital Sinus: prenatal diagnosis and pregnancy complications. Am J Obstet gynecol. 1997 Mar:176(3):709-11.

9)Arena F. Racchiusa S, Proietto F, Romeo C, Aloisi G, Cruccetti A, Zimbaro G, Romeo G. Urinary hydrometrocolpos by persistent Urogenital sinus. Pediatr Med Chir. 1988 Jan-Feb;20(1):75-9.

10)Muller R, Dohman S. Hydrometrocolpos causing progressive unilateral  hydronephrosis in agenesis of the contralateral kidney. Zentralbl Gynakkol, 2000; 122(11):581-4.

11)Hahn-Pedersen J, Kvist N, Nielsen OH. Hydrometrocolpos: current view on pathogenesis and management. J Urol. 1984 sep;132(3):537-40.

12)Arena F., Romeo C., Cruccetti A., Antonuccio P., Basile M., Romeo G. The Neonatal management and surgical correction of urinary hydrometrocolpos caused by a persistent Urogenital Sinus. BJU Int. 1999 Dec:84(9):1063-8.