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Septate uterus

A septate uterus is a common type of congenital uterine anomaly, and it may lead to an increased rate of pregnancy loss. The main imaging differential diagnoses are arcuate uterus and bicornuate uterus.

Epidemiology

It is considered the commonest uterine anomaly (accounts for ~55% of such anomalies). It is classified as a class V Mullerian duct anomaly. Septate uterus is the most common anomaly associated with reproductive failure (67%).

Pathology

Septate uterus is considered a type of uterine duplication anomaly. It results from partial or complete failure of resorption of the uterovaginal septum after fusion of the para-mesonephric ducts. The septum is usually fibrous but can also have varying muscular components.

Subtypes
  • a partial septum (sub-septate 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
Associations

As with other uterine anomalies, concurrent renal anomalies may be associated

Radiographic features  

General
  • the external uterine fundal contour may be convex, flat, or mildly (< 1 cm) concave
  • acute angle <75 degrees between uterine cavities
  • endometrial canals are completely separated by tissue iso-echoic to myometrium with extension into endocervical canal
Ultrasound

The echogenic endometrial stripe is separated at the fundus by the intermediate echogenicity septum. The septum extends to the cervix in a complete septate uterus. The external uterine contour must demonstrate a convex, flat, or mildly concave (ideally <1cm) configuration and may best be appreciated on coronal images of the uterus. 

Colour Doppler

May show vascularity in the septum in 70% of cases; and if present may be associated with a higher rate of obstetric complications 8

Fluoroscopy - Hysterosalpingogram

Accuracy of hysterosalpingogram alone is only 55% for differentiation of septate uterus from bicornuate uterus. An angle of less than 75° between the uterine horns is suggestive of a septate uterus, and an angle of more than 105° is more consistent with bicornuate uteri. Unfortunately, the majority of angles of divergence between the horns fall between these ranges, and considerable overlap between the two anomalies is noted.

Pelvic MRI

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), myometrium (intermediate signal), or both 2.

Complications

  • 90% miscarriage rate 
    • a patient with a septate uterus does not usually not have difficulty conceiving, but a septate uterus is associated with the highest rate of pregnancy loss of the Müllerian duct anomalies

Treatment and prognosis

The distinction between septate uterus and bicornuate uterus has important management implications. In septate uterus, but not in bicornuate uterus, the septum can be shaved off during hysteroscopy (metroplasty) to form a single uterine cavity without perforating the uterus 4.

Reproductive outcome has been shown to improve after resection of the septum, with reported decreases in the spontaneous abortion rate from 88% to 5.9% after hysteroscopic metroplasty.

Differential diagnosis

Considerations a hysterosalpingogram include

  • bicornuate uterus: the shape of the external uterine contour is crucial to differentiate a septate uterus from a bicornuate uterus, because widely different clinical and interventional approaches are assigned to each anomaly.

On ultrasound or MRI images also consider


Related articles

Abdominal and pelvic anatomy
Ultrasound

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