Caesarean Scar Niche

Caesarean scar niche is a wedge-shaped or triangular indentation of at least 2 mm depth in the myometrium at the site of the caesarean scar, seen on ultrasound as a collection of fluid or blood in the scar. It is caused by incomplete healing and is found in 50 to 60 percent of women after caesarean section, and it is larger after several operations. It matters because it can cause postmenstrual bleeding, pelvic pain and subfertility, and increases the risk of scar pregnancy.

• Risk factors: multiple caesarean sections, retroflexed uterus, low incision, labour at full dilatation, single layer closure, diabetes.
• Big niches (above 50 percent of wall thickness) cause more symptoms.
• Symptoms usually appear within a year of surgery.

Women have brown spotting for several days after menstruation, intermenstrual bleeding, dysmenorrhoea, chronic pelvic pain, dyspareunia or difficulty conceiving. Examination is often normal, with scar tenderness in some.

• Postmenstrual spotting for 2 or more days.
• Pain at the scar site during the period.
• Differential diagnosis: endometrial polyp, adenomyosis, endometriosis, chronic endometritis, cervical ectropion, hormonal bleeding, intrauterine adhesions.
• Complications: abnormal uterine bleeding, pain, secondary infertility, scar pregnancy, placenta accreta spectrum, scar rupture in pregnancy, dyspareunia.

The approach is transvaginal ultrasound, with saline infusion for clearer views.

• Transvaginal ultrasound in the early follicular phase: niche depth (2 mm or more), width, length, residual myometrial thickness, and position in relation to the cervix.
• Saline infusion sonohysterography to define the niche edges; hysteroscopy for direct vision.
• MRI for complex niches or before surgery.
• Pregnancy test; endometrial sampling if bleeding is heavy or the woman is above 45 years.

The principle is treatment of symptoms, with surgery for troublesome niches and for women who want fertility.

• Supportive: menstrual diary; reassurance that treatment is not needed without symptoms; avoid pregnancy for 18 to 24 months after a caesarean section; reduce risk at the next operation with two layer closure.
• Pharmacological: combined oral contraceptive pill with ethinylestradiol 30 micrograms and levonorgestrel 150 micrograms oral once daily, continuous or cyclic, for postmenstrual bleeding; 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 pain; doxycycline 100 mg oral 12-hourly for 14 days if chronic endometritis is proved.
• Procedures: hysteroscopic resection of the lower edge of the niche (residual myometrium of 3 mm or more); laparoscopic or vaginal niche repair with excision and layered closure (residual myometrium below 3 mm); embryo transfer in assisted conception placed away from the niche; hysterectomy when childbearing is complete and symptoms are severe.
• Special groups: women with infertility and a large niche have repair before assisted conception; pregnant women with a niche have a scan at 6 weeks for scar pregnancy and a scar thickness scan at 35 to 37 weeks.
• Red flags: heavy bleeding, pain with a positive pregnancy test, fever above 38 degrees Celsius, scar tenderness in pregnancy.
• Follow-up: review at 3 months to check bleeding; ultrasound before pregnancy; early scan at 6 weeks of any pregnancy.