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A septate uterus is the most common type of congenital uterine anomaly, and may lead to an increased rate of pregnancy loss. The main imaging differential diagnoses are arcuate uterus and bicornuate uterus.
It is considered the most common uterine anomaly (accounts for ~55% of such anomalies). It is classified as a class V Müllerian duct anomaly.
Septate uterus is the most common anomaly associated with subfertility, preterm labor, and reproductive failure (67%), affecting ~15% of women with recurrent pregnancy loss 11,12.
As with other uterine anomalies, concurrent renal anomalies may be associated.
Septate uterus is considered a type of uterine duplication anomaly. It results from the partial or complete failure of resorption of the uterovaginal septum after fusion of the paramesonephric ducts. The septum is usually fibrous but can also have varying muscular components.
- a partial septum (subseptate uterus) involves the endometrial canal but not the cervix
- a septum is considered "complete" if it extends to either the internal or external cervical os 10
- septum extends into the vagina: septate uterus and vagina
The external uterine fundal contour may be convex, flat, or mildly (<1 cm) concave. There is an acute angle (<75°) between the uterine cavities, which are completely separated by a septum that may extend into the endocervical canal.
Accuracy of hysterosalpingogram alone is only 55% for the differentiation of a septate uterus from a bicornuate uterus. An angle of <75° between the uterine horns is suggestive of a septate uterus, and an angle of >105° is more consistent with a bicornuate uterus. Unfortunately, the majority of angles of divergence between the horns fall between these ranges, and there is considerable overlap between the two anomalies.
The echogenic endometrial stripe is separated at the fundus by the intermediate echogenicity septum (which is isoechoic to myometrium). In a complete septate uterus, the septum extends to the cervix. The external uterine contour must demonstrate a convex, flat, or mildly concave (ideally <1 cm) configuration and may best be appreciated on coronal images of the uterus.
Color Doppler may show vascularity in the septum (70% of cases) which, if present, may be associated with a higher rate of obstetric complications 8.
MRI is considered the current imaging modality of choice.
On MR images, the septate uterus is generally normal in size and each endometrial cavity appears smaller than the configuration of a normal cavity.
The septum may be composed of fibrous tissue (low T2 signal intensity), myometrial tissue (intermediate signal), or both 2.
Treatment and prognosis
The distinction between a septate uterus and a bicornuate uterus has important management implications. In a septate uterus, the septum can be shaved off during hysteroscopy (metroplasty) to form a single uterine cavity without perforating the uterus 4.
The reproductive outcome has been shown to improve after resection of the septum, with reported decreases in the spontaneous abortion rate from 88% to 6% after hysteroscopic metroplasty.
Considerations on hysterosalpingogram include:
- bicornuate uterus: the shape of the external uterine contour is crucial to differentiate a septate uterus from a bicornuate uterus because the clinical and interventional approaches differ widely for each anomaly
On ultrasound or MRI, also consider:
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