Unicornuate uterus

A unicornuate uterus or unicornis unicollis is a type of Mullerian duct anomaly (class II).  This type can account for ~10% (range 6-13%) of uterine anomalies and infertility is seen in ~12.5% (range 5-20%) of cases.

Pathology

There is a failure of one müllerian duct to elongate while the other develops normally. The embryologic predominance of the unicornuate uterus to be on the right has not been explained. It may or may not have a rudimentary horn.

Sub-classification

It can be classified into to the following types according to the American Fertility Society 3.

  • type a: with rudimentary horn 
    • a1: horn contains endometrium
      • a1a: communicating contralateral rudimentary horn contains endometrium (10%)
      • a1b: non-communicating contralateral rudimentary horn contains endometrium (22%)
    • a2: contralateral horn has no endometrial cavity (33%)
  • type b: no horn (35%)
Associations
  • renal abnormalities
    • renal anomalies are more commonly associated with a unicornuate uterus than with other müllerian duct anomalies and are present in 40% of cases, e.g. renal agenesis
    • the renal anomaly is always ipsilateral to the rudimentary horn
  • cryptomenorrhea within endometrium containing rudimentary horn that does not communicate with the endometrial cavity
  • primary infertility 4

Radiographic features

Hysterosalpingogram (HSG)

The endometrial cavity usually assumes a fusiform (banana type) shape (except for type a where there may a small cavitation filling defect), tapering at the apex and draining into a solitary fallopian tube. The uterus is generally shifted off the midline.

Ultrasound

Can be difficult to detect on ultrasound. The uterus may be seen tapering to one side.

MRI
  • unicornuate uterus appears curved and elongated, with the external uterine contour assuming a banana shape
  • uterine volume is reduced, and the configuration of the uterus is asymmetric
  • normal myometrial zonal anatomy is maintained

Treatment and prognosis

Of the Mullerian duct anomalies, a unicornuate uterus is considered to have the second worst obstetric outcome (worst with a septate uterus).

Spontaneous abortion rates are reported to range from 41-62%. Reported premature birth rates range from 10-20%. Fetal survival rate is ~40% (range 38-57%).

Differential diagnosis 

  • bicornuate bicollis
    • two cervical canals
    • cannulation of only one of these canals may mimic unicornuate uterus on a hysterosalpingogram 

Related articles

Abdominal and pelvic anatomy

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