Classification and developmental features
Müllerian duct pathologies are classified according to the mechanism and stage of their developmental disruption.
- Unicornuate uterus (Unicornuate Uterus) and rudimentary horn. Often accompanied by a second, underdeveloped (rudimentary) horn. It may or may not contain functional endometrium. If a functional horn does not communicate with the main uterine cavity, menstrual blood accumulates within it, leading to haematometra (haematometra) and significantly increasing the risk of endometriosis (endometriosis).
- Uterine didelphys (Uterus Didelphys, Class III). Results from complete failure of Müllerian duct fusion. This produces two fully developed uterine horns and two cervices. In 75% of cases, this pathology is associated with a longitudinal vaginal septum.
- Bicornuate uterus (Bicornuate Uterus, Class IV). The result of incomplete fusion of the cranial segments of the ducts followed by resorption of the septum. The degree of non-fusion of the horns directly correlates with the severity of potential obstetric complications.
- Septate uterus (Septate Uterus, Class V). The most common anomaly. It forms due to incomplete resorption of the fibrous tissue between the horns. The septum may be partial or complete (reaching the external os). This anomaly is associated with the worst obstetric outcomes.
- Arcuate uterus (Arcuate Uterus, Class VI). Considered an anatomical variant of normal. Does not cause fertility issues.
- Diethylstilbestrol-related anomalies (Class VII). In utero exposure to this synthetic estrogen leads to uterine hypoplasia and the formation of a characteristic T-shaped cavity.
Diagnostic imaging and MRI semiotics
Ultrasound, hysterosalpingography (HSG), and magnetic resonance imaging (MRI) are used to evaluate pelvic anatomy. MRI is the gold standard for precise differential diagnosis.
Key imaging patterns:
- Unicornuate uterus: T2-weighted images (T2WIs) or HSG demonstrate the characteristic "banana-shaped" configuration of the cavity.
- Arcuate uterus: coronal MRI scans and HSG reveal a smooth, broad indentation of the fundal cavity with a completely even outer myometrial contour.
- Uterine didelphys: ultrasound and MRI clearly visualize two widely spaced, normal-sized horns with preserved zonal anatomy, two cervices, and (frequently) two vaginae.
Differential diagnosis between a bicornuate uterus and a septate uterus is of particular importance, as treatment approaches (such as the need for hysteroscopic metroplasty) differ fundamentally.
| MRI finding (T2WI, coronal plane) | Bicornuate uterus | Septate uterus |
|---|---|---|
| Outer contour of the uterine fundus | Cleft (indentation) $\ge$ 1 cm | Convex, flat, or indentation $\le$ 1 cm |
| Structure of the dividing element | Myometrium with normal signal intensity | Fibrous tissue (low signal intensity) and muscular component |
Vaginal anomalies and obstructive conditions
Defects in vertical or lateral fusion of the Müllerian ducts can lead to the formation of vaginal septa or complete vaginal agenesis (as seen in Mayer-Rokitansky-Küster-Hauser syndrome).
The most frequently detected anomaly is imperforate hymen (prevalence 0.1%). Clinically, it presents as a thin, bulging, bluish membrane visible upon inspection. In such typical cases, additional imaging is unnecessary. However, for a thicker transverse vaginal septum, MRI is required for surgical planning—on sagittal T2WIs, the septum appears as a zone of low-signal fibrous tissue with loss of normal zonal anatomy.
Outflow obstruction leads to fluid accumulation:
- In the vagina — haematocolpos (haematocolpos).
- In the vagina and uterine cavity — haematometrocolpos (haematometrocolpos).
On MRI, these conditions are characterized by vaginal distension with intraluminal fluid containing sedimentation levels. Blood breakdown products produce an intermediate signal on T2WIs and a high signal on fat-suppressed T1WIs. Asymmetric obstructions also occur: for example, in uterine didelphys, one horn may drain normally while haematocolpos develops in the second horn due to an imperforate hymen.
Briefly: answers to topical questions
Which urinary tract developmental anomalies are most commonly associated with Müllerian duct malformations?
The most frequent associated urinary tract malformations are described in Mayer-Rokitansky-Küster-Hauser syndrome: they occur in approximately one-third of cases and include:
- Renal ectopia (dystopia renis), such as pelvic kidney.
- Renal duplication.
- Renal agenesis (renal agenesis).
What anatomical defects are part of Mayer-Rokitansky-Küster-Hauser syndrome in addition to vaginal agenesis?
In addition to the absence of the upper vagina, Mayer-Rokitansky-Küster-Hauser syndrome (Mayer–Rokitansky–Küster–Hauser syndrome) includes complete or partial absence of the uterus. The main anatomical features and associated defects include:
- Uterine agenesis or hypoplasia — underdevelopment or absence of the organ with intact ovaries and fallopian tubes.
- Urinary tract malformations — occurring in one-third of cases, including renal ectopia (e.g., pelvic kidney), renal duplication, or renal agenesis.
Class and exam questions
How to differentiate a bicornuate uterus from a septate uterus on MRI?
The primary criterion is the shape of the outer contour of the uterine fundus. In a bicornuate uterus, there is a cleft with a depth of 1 cm or more, whereas in a septate uterus, the outer contour remains convex, flat, or has a minor indentation (less than 1 cm).
What are the risks associated with a rudimentary uterine horn?
If the rudimentary horn contains functional endometrium but lacks communication with the main uterine cavity, blood accumulates within it (haematometra). This causes cyclic pain and significantly increases the risk of endometriosis.
Is MRI required to diagnose an imperforate hymen?
No, in typical cases the diagnosis is made clinically upon physical examination (bulging bluish membrane). MRI is indicated for surgical planning in more complex obstructive malformations, such as a thick transverse vaginal septum.
What else to study on this topic
- MRI semiotics and surgical planning for transverse vaginal septa
- Diagnostic imaging in disorders of sex development (Turner syndrome, androgen insensitivity syndrome)
- Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome: anatomical features
- Hysterosalpingography (HSG): diagnostic utility in Müllerian duct anomalies
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