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 the following types according to the American Fertility Society:
- type a: with rudimentary horn
- 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
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.
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
Treatment and prognosis
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