Caesarean Scar Defect

Caesarean scar defect is a thin or incomplete area of healing in the uterine wall at the caesarean scar, shown by a residual myometrial thickness of less than 3 mm or an area of absent muscle. It results from poor healing after single layer closure, infection, low incision near the cervix, retroflexed uterus and repeat surgery.

It affects up to 60 percent of scars on ultrasound. It matters because thin scars can cause scar dehiscence or rupture in labour and scar pregnancy.

• Risk factors: multiple caesarean sections, labour before surgery, low cervical incision, single layer closure, retroflexed uterus, infection, obesity.
• Many defects cause no symptoms.
• Thin scar thickness in late pregnancy predicts rupture.

Most women have no symptoms. Some have postmenstrual spotting, dysmenorrhoea, chronic pelvic pain, dyspareunia or subfertility, and in pregnancy, scar tenderness or bleeding.

• Brown spotting for 2 or more days after the period.
• Scar tenderness on bimanual examination.
• Differential diagnosis: endometriosis, adenomyosis, endometrial polyp, chronic endometritis, cervical polyp, intrauterine adhesions, fibroids.
• Complications: abnormal uterine bleeding, pain, infertility, caesarean scar pregnancy, placenta accreta spectrum, scar dehiscence, uterine rupture in labour.

The approach is transvaginal ultrasound, with fluid enhanced views where needed.

• Transvaginal ultrasound in the early follicular phase or after saline infusion (sonohysterography): defect size, depth and width, residual myometrial thickness (below 3 mm is thin), position relative to the internal os.
• In pregnancy at 35 to 37 weeks: lower segment thickness (below 2.3 mm is a concern, below 2.0 mm is high risk).
• Hysteroscopy for a defect with symptoms, and MRI for complex cases.
• Pregnancy test and cervical screening where indicated.

The principle is no treatment for a defect with no symptoms, symptom control for bleeding and surgical repair for troublesome or high risk defects.

• Supportive: counselling; menstrual diary; plan the birth of any later pregnancy early; avoid conception for 18 to 24 months after a caesarean section.
• Pharmacological: combined oral contraceptive pill with ethinylestradiol 30 micrograms and levonorgestrel 150 micrograms oral once daily taken continuously or in 21 day packs for postmenstrual spotting.
• Levonorgestrel intrauterine system 52 mg for 5 years.
• Tranexamic acid 1 g oral 8-hourly for 4 days during bleeding.
• Ibuprofen 400 mg oral 8-hourly with food for dysmenorrhoea.
• Procedures: hysteroscopic resection of the lower edge of the niche when residual myometrium is 3 mm or more and the woman has spotting and does not plan pregnancy soon.
• Laparoscopic, robotic or vaginal repair with excision of scar and layered closure when residual myometrium is below 3 mm and the woman has symptoms or plans pregnancy.
• Hysterectomy for severe symptoms when childbearing is complete.
• Special groups: pregnant women with a thin scar (below 2.0 mm) have planned caesarean section at 36 to 37 weeks and 6 days; women with a previous scar pregnancy need early scan at 6 weeks.
• Red flags: heavy bleeding, scar pain in pregnancy, fever above 38 degrees Celsius, positive pregnancy test with pain or bleeding.
• Follow-up: review in 3 months after treatment; ultrasound before the next pregnancy and early scan at 6 weeks; review at 6 weeks after repair.