What Are the Types of Uterine Malformations?

Uterine malformations are diverse and primarily include congenital absence of the uterus, unicornuate uterus, bicornuate uterus, rudimentary horn uterus, and septate uterus.

① Congenital Absence of the Uterus

Congenital absence of the uterus results from failure of fusion and subsequent regression of the uterine segments of both paramesonephric (Müllerian) ducts. It is commonly associated with vaginal agenesis. A “primordial uterus” arises when the two paramesonephric ducts fuse but then cease development shortly thereafter, resulting in an extremely small uterus measuring only 1–3 cm in length. Most primordial uteri lack a uterine cavity altogether or consist of a solid, muscular structure without endometrium, and thus menstruation does not occur. Rarely, a primordial uterus may contain a cavity and endometrium. Ovarian development is typically normal in both conditions.

② Unicornuate Uterus

A unicornuate uterus develops when only one paramesonephric duct develops normally, forming a single-horned uterus; ovarian function on the same side remains normal. The contralateral paramesonephric duct either fails to develop entirely or does not form a patent duct. Consequently, the ovary, fallopian tube, and kidney on the undeveloped side are often absent. A unicornuate uterus is frequently asymptomatic; physical examination reveals a small, fusiform uterus deviated from the midline. When accompanied by a rudimentary horn, a small, firm mass may be palpable on the opposite side of the uterus.

③ Bicornuate Uterus

A bicornuate uterus results from incomplete fusion of the two paramesonephric ducts and is classified as either complete (with divergence beginning at the internal cervical os) or incomplete (with divergence occurring above the internal cervical os).

④ Rudimentary Horn Uterus

In a rudimentary horn uterus, one paramesonephric duct develops normally while the lower-to-mid portion of the contralateral duct fails to develop properly, resulting in a rudimentary horn. The ovary and fallopian tube on the rudimentary horn side are usually normal, but ipsilateral urinary tract anomalies are common. Rudimentary horn uterus frequently coexists with unicornuate uterus, accounting for approximately 65% of cases.

⑤ Septate Uterus

A septate uterus results from impaired resorption of the midline septum following fusion of the two paramesonephric ducts. Clinically, it is categorized as either complete (the septum extends from the uterine fundus to below the internal cervical os) or incomplete (the septum terminates above the internal cervical os).