Why do niches develop in Caesarean uterine scars? Hypotheses on the aetiology of niche development

Abstract

Caesarean section (CS) results in the occurrence of the phenomenon 'niche'. A 'niche' describes the presence of a hypoechoic area within the myometrium of the lower uterine segment, reflecting a discontinuation of the myometrium at the site of a previous CS. Using gel or saline instillation sonohysterography, a niche is identified in the scar in more than half of the women who had had a CS, most with the uterus closed in one single layer, without closure of the peritoneum. An incompletely healed scar is a long-term complication of the CS and is associated with more gynaecological symptoms than is commonly acknowledged. Approximately 30% of women with a niche report spotting at 6-12 months after their CS. Other reported symptoms in women with a niche are dysmenorrhoea, chronic pelvic pain and dyspareunia. Given the association between a niche and gynaecological symptoms, obstetric complications and potentially with subfertility, it is important to elucidate the aetiology of niche development after CS in order to develop preventive strategies. Based on current published data and our observations during sonographic, hysteroscopic and laparoscopic evaluations of niches we postulate some hypotheses on niche development. Possible factors that could play a role in niche development include a very low incision through cervical tissue, inadequate suturing technique during closure of the uterine scar, surgical interventions that increase adhesion formation or patient-related factors that impair wound healing or increase inflammation or adhesion formation.

Keywords: Caesarean section; abnormal uterine bleeding; adhesion formation; cervix; niche; scar; spotting; surgical techniques; uterus.

Figure 1

Image of a niche using transvaginal ultrasound in mid-sagittal and transversal plane and a schematic diagram of a niche and hysteroscopic image. (a) Mid-sagittal plane; (b) transversal plane; (c) schematic diagram of a niche; (d) niche seen by hysteroscopy, the internal os is out of the scope of this picture.

Figure 2

Laparoscopic view on a mucus-containing large niche that is located in the lower cervix. Mucus is expelled during a laparoscopic niche resection after dissection of the bladder and opening of the niche.

Figure 3

Schematic diagram of incomplete closure of the myometrium and counteracting forces on the uterine scar due to the retraction of adhesions between the scar and the abdominal wall in a retroflected uterus. (a) Single-layer closure of the uterus may increase niche formation due to greater risk of incomplete closure. (b) Counteracting forces on the Caesarean section uterine scar, due to retraction of adhesions between the uterine scar and the abdominal wall in a retroflected uterus, may impair wound healing and increase the formation of niches.

Figure 4

Laparoscopic image of a uterus with a large niche, illumination of the hysteroscopic light in the niche can be seen directly under the adhesions attached to the niche. Adhesions between the niche and the abdominal wall seen during laparoscopy (a), owing to the diaphany of the combined hysteroscopy it can be seen that the adhesions are located at the deepest point of the niche. Hysteroscopic image of the combined of a part of the large niche surface be seen in (b).

Figure 5

Macroscopic image of a uterus with a niche, removed by laparoscopy because of abnormal uterine bleeding and dysmenorrhoea. Note that the adhesions are located at the deepest point of (a relatively small) niche.

Figure 6

Laparoscopic view on adhesions between the lower uterine segment and the bladder at the site of a niche.