# Caesarean Scar Niche and Isthmocele

> NEET-PG Obstetrics and Gynaecology notes on caesarean scar niche, covering isthmocele symptoms, ultrasound diagnosis, scar pregnancy and surgical repair.

- Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/caesarean-scar-niche-and-isthmocele
- Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-15
- Last updated: 2026-10-15
- Reference basis: Williams Obstetrics; Dutta's Textbook of Obstetrics
- How to cite: "Caesarean Scar Niche and Isthmocele", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/caesarean-scar-niche-and-isthmocele

## Direct answer

A caesarean scar niche, also called an isthmocele, is a focal defect in the uterine scar where myometrial healing is incomplete after caesarean section. It is seen as a hypoechoic gap on transvaginal ultrasound, and its classic symptom is post-menstrual spotting, with infertility and scar pregnancy as less common associations. Asymptomatic niches are followed up, while symptomatic ones are considered for hysteroscopic or laparoscopic repair.

## What you must remember

- **Definition:** an isthmocele is a niche or indentation at the caesarean scar, reflecting incomplete myometrial healing at the lower uterine segment.
- **Diagnosis:** transvaginal ultrasonography, often with saline infusion, shows a hypoechoic defect, and residual myometrial thickness is measured at its thinnest point, where thinning below about 3 mm is commonly regarded as significant.
- **Classic symptom:** post-menstrual spotting, a brownish discharge that persists for days after the period ends.
- **Other symptoms:** heavy or prolonged menses, dysmenorrhoea, pelvic pain and subfertility, though these are less specific.
- **Risk factors:** caesarean in labour, obesity, uterine infection, and surgical closure technique, with some studies linking single-layer and locked closure to larger niches.
- **Scar pregnancy:** implantation within the niche is a dangerous form of ectopic pregnancy that threatens uterine rupture and haemorrhage if not treated early.
- **Management:** asymptomatic niches are observed, while symptomatic women or infertile women with large defects may need hysteroscopic resection or laparoscopic or open repair.

## A stepwise approach to a symptomatic niche

A woman with post-menstrual spotting after a caesarean needs the niche excluded before the symptom is put down to hormones. The steps below follow the usual evaluation.

1. **Confirm the niche:** perform transvaginal ultrasound at a suitable point in the cycle, measuring the depth, width and residual myometrial thickness of the defect at its thinnest point.
2. **Exclude pregnancy:** check a pregnancy test and look for a gestational sac within the niche, because scar pregnancy must be ruled out before any procedure.
3. **Assess the symptoms:** determine whether the complaints are spotting, pain or subfertility, since asymptomatic niches need only observation.
4. **Choose the repair:** hysteroscopic resection suits many symptomatic niches, while laparoscopic or open reconstruction is used for large or deep defects, especially in women planning pregnancy.
5. **Plan the next pregnancy:** arrange ultrasound review after repair, and early scans in any future pregnancy to check the scar and the placental position.

## Where the exam tries to catch you

Questions here test whether you attribute spotting to the scar rather than to hormones.

- **Trap:** Calling every post-caesarean spotting a menstrual disorder. — **Correct:** Post-menstrual spotting after caesarean is the classic sign of a niche, so ultrasound is needed before attributing it to hormones.
- **Trap:** Operating on an asymptomatic niche found incidentally. — **Correct:** Asymptomatic niches are followed up, and surgery is reserved for symptoms or for infertility with a large defect.
- **Trap:** Missing a scar pregnancy because the niche looks like an ordinary defect. — **Correct:** Implantation within the niche is an ectopic pregnancy that threatens rupture and haemorrhage, so a gestational sac must be looked for in any woman with a niche and a positive test.

## Frequently asked questions

### Which investigation confirms a caesarean scar niche?
Transvaginal ultrasonography, often with saline infusion, confirms a caesarean scar niche by showing a hypoechoic defect at the scar. Residual myometrial thickness is measured at the thinnest point to grade the defect.

### What is the classic symptom of an isthmocele?
Post-menstrual spotting, a brownish discharge occurring for several days after the period ends, is the classic symptom of an isthmocele. Some women also report heavy or prolonged periods, pelvic pain or subfertility.

### Is an asymptomatic caesarean scar niche treated?
An asymptomatic caesarean scar niche is generally observed without treatment. Repair is reserved for women with symptoms such as spotting or pain, or for infertile women with a large niche.

### What is caesarean scar pregnancy?
Caesarean scar pregnancy is implantation of a gestational sac in a niche at the caesarean scar, and it is a form of ectopic pregnancy. It carries a risk of haemorrhage and uterine rupture, so it needs early identification and treatment.

### Can a caesarean scar niche be prevented?
Surgical technique at caesarean is the main factor that can be modified to reduce niche formation. Evidence on the best closure method remains mixed, so surgeons aim for careful myometrial apposition and secure haemostasis at closure.