Incomplete canalisation of the genital canal results in three types of obstructions: imperforate hymen, transverse vaginal septum and/or atresia of the vagina. All female genital structures arise from the paramesonephric ducts. These ducts fuse to become a single genital canal caudally, which is usually completed by 10 weeks. The uterus and part of the vagina arise from this structure. The hymen is the partition between the dilated, canalised, fused sinovaginal bulbs and the urogenital sinus. Many anomalies of the uterus and vagina result from incomplete fusion of the paramesonephric ducts early in the fetal period. Hydrometrocolpos is a result of these obstructive lesions which lead to an accumulation of mucoid secretions in the uterus and, often, vagina. In mild cases, the obstruction may not be apparent until puberty. In severe cases, massive abdominal distension and uterine dilatation result. Enlargement of the vagina into the abdominal cavity may lead to ureteric obstruction and hydronephrosis. Hydrometrocolpos can also result from maternal estrogen exposure leading to an increased production of mucoid material by the uterine glands. This is a rare condition, occurring in approximately 1/16,000 female births.


The diagnosis of the hydrometrocolpos should be considered when a cystic or solid mass is noted in the pelvis of a female fetus. The finding may instead be that of an identifiable fluid-filled uterus. Low level echoes posterior to the bladder and extending into the abdomen are typical. Occasionally a mass will be seen bulging from the perineum. Hydronephrosis and/or hydroureter may accompany hydrometrocolpos. Associated anomalies include renal agenesis, polycystic kidneys, oesophageal atresia, duodenal atresia, imperforate anus, bicornuate uterus and caudal regression syndrome. Associated anomalies are more commonly found with higher” obstructions. No case has been reported before the 3rd trimester, probably because the build-up of secretions is under maternal hormonal control, which is insufficient before this time.”

Differential Diagnosis

Renal tract dilatation usually caused by an obstructive uropathy can cause the appearance of a cystic lesion in the abdomen. Ovarian, mesenteric or urachal cysts include cystic structures in the fetal abdomen of a female fetus with normal gastrointestinal and urinary tracts. Urachal cysts can be found in association with bladder obstruction. Sacral tumours, including chondromas, teratomas or solid ovarian tumours should be considered if the mass appears to be solid. The differential from megacystis can be difficult, since both involve fluid-filled spaces in the abdomen associated with hydronephrosis. Anorectal atresia produces a dilated (U-shaped) cystic mass in the distal colon. There may be decreased amniotic fluid. Persistent cloaca may produce a septated cystic mass with decreased fluid; also more common in females.

Sonographic Features

Large cystic mass in the pelvis of a female fetus

Fluid-filled uterus in a female fetus

May be associated with hydronephrosis/hydroureter; if so, amniotic fluid volume may be diminished

Cystic or solid structure may be seen bulging from perineum

Associated Syndromes

  • Dexamethasone exposure
  • Ellis van Creveld
  • Familial hydrometrocolpos
  • McKusick Kaufmann
  • Turner


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