Unicornuate uterus

A unicornuate uterus or unicornis unicollis is a type of Mullerian duct anomaly (class II) that is the second most commonly associated with miscarriages. 

This type can account for ~10% (range 6-13%) of uterine anomalies and infertility is seen in ~12.5% (range 5-20%) of cases.

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.

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%)
  • 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

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 single fallopian tube. The uterus is generally shifted off the midline.

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

  • 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

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%).

  • bicornuate bicollis
    • two cervical canals
    • cannulation of only one of these canals may mimic unicornuate uterus on a hysterosalpingogram 
Abdominal and pelvic anatomy
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Article information

rID: 6979
System: Gynaecology
Section: Anatomy
Synonyms or Alternate Spellings:
  • Uni-cornuate uterus
  • Unicornis unicollis

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Cases and figures

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    Unicornuate uterus
    Figure 1: unicornuate uterus - type b
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     Case 1
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    Case 2
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    Case 3
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    Case 3: on 3D ultrasound
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    Case 4
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    Case 6
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