Unicornuate uterus

Last revised by Mostafa El-Feky on 13 Mar 2023

A unicornuate uterus or unicornis unicollis is a type of Müllerian duct anomaly (class II) characterized by a banana-shaped uterus usually draining into a single fallopian tube.

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

  • 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

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 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%)

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

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

  • curved and elongated uterus: banana-shaped external uterine contour
  • reduced uterine volume
  • asymmetric uterine configuration
  • normal myometrial zonal anatomy

Of the Müllerian duct anomalies, a unicornuate uterus is considered to have the second-worst obstetric outcome (the worst is 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 

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Cases and figures

  • Figure 1
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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 5
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  • Case 6
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  • Case 7: with rudimentary left horn
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  • Case 8
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  • Case 9
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  • Case 10
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  • Case 11
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  • Case 12
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  • Case 13
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  • Case 14: type B
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  • Case 15: type a1b
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  • Case 16
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  • Case 17: unicornuate uterus (3D ultrasound)
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  • Case 18
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  • Case 19
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  • Case 20
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  • Case 21
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  • Case 22
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  • Case 23: with blocked fallopian tube
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  • Case 24
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  • Case 25
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  • Case 26: with hematometra in non-communicating contralateral rudimentary horn
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