Cesarean Scar Niche (Isthmocele): Measurement Technique and Residual Myometrium on Ultrasound
Cesarean scar niche (isthmocele) is a myometrial defect in the area of the previous incision, detected on ultrasound examination. The key assessment parameter is residual myometrial thickness — the thickness of tissue between the defect zone/gestational sac and the bladder wall.
Residual Myometrium: Values from Fragments
In the cited sources, residual myometrial thickness is measured in millimeters and serves as a criterion for implantation severity in pregnancy in the scar. The following clinical examples are presented:
| Clinical Scenario | Residual Myometrium |
|---|---|
| Pregnancy in scar (example a) | 3.6 mm |
| Pregnancy in scar, gestational sac partially in scar, majority in cavity (example b) | 2.3 mm |
| Gestational sac completely implanted in scar myometrium, prolapsing toward bladder (example c) | Residual myometrium between gestational sac and bladder is absent |
According to the fragment, during marking the gestational sac is outlined, and the residual myometrium is designated by a separate line — that is, measurement is performed as the distance (thickness) of the myometrial layer in the defect zone.
Measurement Technique
Assessment of residual myometrium is based on visualization of the tissue layer between the defect (niche or gestational sac) and the bladder wall. The specific measurement protocol for niche outside pregnancy (length, depth, width of defect, scanning planes) is not detailed in the provided fragments — [clarification needed].
Clinical Significance
Reduction in residual myometrial thickness (in the cited examples — from 3.6 mm to complete absence) reflects the degree of gestational sac penetration into the scar area and bladder wall involvement. Questions regarding myometrial healing after cesarean delivery and post-cesarean scarring are addressed in the cited periodicals (Ultrasound in Obstetrics & Gynecology, 2024), however, numerical thresholds for isthmocele classification are not provided in these fragments — [clarification needed].
Frequently asked questions
What is residual myometrium in scar niche assessment?
It is the thickness of the myometrial layer between the defect zone (niche or gestational sac) and the bladder wall. Measured in millimeters.
What residual myometrium values are presented in the sources?
In examples of pregnancy in scar — 3.6 mm and 2.3 mm; with complete implantation of the gestational sac into scar myometrium, residual myometrium between the sac and bladder may be absent.
How is residual myometrium designated during marking?
The gestational sac is outlined separately, and residual myometrium is designated by a separate line; measured as the thickness of the tissue layer in the defect zone.
Are there threshold criteria for isthmocele outside pregnancy in the sources?
In the provided fragments, specific threshold values and measurement protocol for niche outside pregnancy are not specified — [clarification needed].