Uterine Window, Definition, Ultrasound, MRI, C-Section Findings, Diagnosis, Radiology

Content:

• Definition
• Ultrasound Findings
• MRI Findings
• C-Section Findings
• Diagnosis
• Radiology Perspective

Definition

A uterine window refers to an area of marked thinning of the lower uterine segment, most commonly occurring at the site of a previous cesarean section scar. In this condition, the myometrium (uterine muscle layer) becomes so thin that the underlying fetal membranes may be visible through it during surgery, giving a “window-like” appearance. Importantly, a uterine window is considered uterine dehiscence, meaning the uterine wall is extremely thin but not completely ruptured.

Unlike a full uterine rupture, the serosal layer remains intact, and there is no complete separation of the uterine wall. However, it indicates increased risk for uterine rupture, especially during labor in women with prior cesarean deliveries.

Ultrasound Findings

On obstetric ultrasound, a uterine window may appear as:

• Marked thinning of the lower uterine segment (often <2–3 mm)
• Loss or discontinuity of the myometrial layer
• Bulging of amniotic sac or fetal parts toward the anterior uterine wall

Transvaginal ultrasound is particularly helpful for measuring lower uterine segment thickness in late pregnancy. However, ultrasound may underestimate or miss subtle dehiscence, and findings must be correlated clinically.

MRI Findings

MRI provides more detailed visualization of the uterine wall layers. Findings may include:

• Focal myometrial thinning at prior cesarean scar
• Intact serosal layer
• Protrusion of gestational sac or fetal membranes toward the abdominal cavity

MRI is particularly useful in complex cases or when differentiating uterine window from placenta accreta spectrum disorders. It helps assess the integrity of uterine layers and surrounding structures.

C-Section Findings

A uterine window is most commonly diagnosed intraoperatively during repeat cesarean section. Surgeons may observe:

• Extremely thin lower uterine segment
• Visible fetal membranes through translucent uterine wall
• No active bleeding or complete rupture

The appearance resembles a transparent membrane instead of normal thick muscle. Although not yet ruptured, this finding indicates a high risk of rupture if labor continues.

Diagnosis

Diagnosis may be:

• Suspected antenatally based on ultrasound thickness measurements
• Confirmed intraoperatively during cesarean delivery

There is no universally accepted thickness cutoff, but lower uterine segment thickness less than 2.0–2.5 mm in late pregnancy raises concern for dehiscence. Clinical context, such as prior cesarean section and symptoms (pain, abnormal fetal heart tracing), also plays a role.

Radiology Perspective

From a radiology standpoint, uterine window represents uterine scar dehiscence without full rupture. Imaging focuses on:

• Measuring myometrial thickness
• Identifying discontinuity of muscle layer
• Excluding associated complications such as placenta accreta or uterine rupture

Radiologists must clearly differentiate between:

• Normal scar thinning
• Uterine window (dehiscence)
• Complete uterine rupture

Accurate reporting helps guide obstetric management decisions, including timing and mode of delivery.