A triangular anechoic defect in the anterior lower segment at the caesarean scar — report its depth, width, length and, most importantly, the residual myometrial thickness above it.
Orient first
- Causes postmenstrual spotting, pain and subfertility; it is the site of caesarean scar pregnancy.
- Residual myometrial thickness under about 3 mm is often the threshold for repair (verify the Delphi consensus your gynaecologists use).
- Saline or gel infusion distends the cavity and improves measurement.
Acquire the study
- Transvaginal ultrasound in the sagittal plane of the uterus; saline or gel infusion sonohysterography where available.
The manoeuvre
- Sagittal view: niche depth and length in mm.
- Transverse view: niche width in mm.
- Residual myometrial thickness in mm and adjacent myometrial thickness for comparison.
- Distance from the niche to the internal os and to the vesicovaginal fold.
- Branches: secondary tracts toward the serosa.
What confirms it
- An indentation of at least 2 mm at the caesarean scar site on the sagittal plane.
What licenses you to exclude it
- A continuous myometrium at the scar in sagittal and transverse views excludes a niche.
The classic misread
- Measuring during menstruation when blood distorts the defect.
- Omitting the residual myometrial thickness.