Etiology of Cesarean Uterine Scar Defect (Niche): Detailed Critical Analysis of Hypotheses and Prevention Strategies and Peritoneal Closure Debate

Abstract

There is an increasing incidence of cesarean scar (CS) defect/niche and its sequelae, probably not entirely explained by better diagnosis or rising cesarean rate. Discussion of possible etiological factors has received scant attention but would be important to formulate preventive strategies. Meaningful informative studies on long-term sequelae of cesarean section are very difficult and none are available for causation of CS defect. Hence, it is crucial to identify key areas in etiology of CS defect for focused research. This practical review proposes an “ischemia and mal-apposition hypothesis for CS niche”, stating that the surgical technique of uterine incision closure is the most important determinant of CS defect formation. Other factors such as cervical location incision, adhesion formation and patient specific factors seem far less important in etiology. Rather than the headline theme of “single versus double-layer closure of uterus”, the finer details of surgical technique which achieve good apposition without inducing tissue ischemia seem more important. Different techniques are discussed and it is proposed that continuous, non-locking absorbable sutures in two layers, without including much of decidua and without undue tight (constricting/devasculaizing) pulling of sutures are likely to result in good healing of uterine scar. Single-layer technique may be best reserved for thin myometrial edges especially during repeat cesareans. Adhesions between uterine isthmus and bladder/abdominal wall seem common associations but not causative for CS niche. It would be desirable to prove these surgical principles by good quality prospective randomized “quantitative” studies but the wait may be very long and this should not hinder the adoption of good surgical principles. Science is much cognitive and not just empirical. To consider a related example, the current recommendation of non-suturing of peritoneal layers during cesarean is mistakenly based on short-term irrelevant surrogate outcomes like analgesic requirements and time-saving, many of which have been already disproven. Evidence is presented recommending simple quick techniques of peritoneal closure to prevent adhesions. More analytical debate in surgical techniques is needed to inspire engaged, critical and insightful practitioners rather than unquestioning dependence on weak evidence/guidance.

Re: Uterine caesarean closure techniques affect ultrasound findings and long‐term maternal outcomes: a systematic review and meta‐analysis

“…This is also consistent with the ‘ischaemia and mal‐apposition hypothesis’ in the development of caesarean scar defects . The thick myometrial edges would be best approximated by a ‘split two‐layer suturing’ without locking or excessive tightening in order to avoid ischaemia of the sutured myometrium …”

“…More importantly, is ‘decidual exclusion’ a simple dichotomous question? The recommendation from most authors/textbooks is much more nuanced with the advice to avoid incorporating too much of the decidua in the suture bites …”

“…The second suture layer is then placed taking transverse wide bites 1–2 cm away from the incision, tightly pulling together the un‐cut myometrium and inverting the broad intervening myometrial area including the incision. This seems a recipe for marked tissue constriction and devascularisation of the myometrial edges (replicated at repeat caesareans) . Otherwise, how can one explain the finding of very thin lower uterine segment not uncommonly following even one caesarean section?…”

“…Otherwise, how can one explain the finding of very thin lower uterine segment not uncommonly following even one caesarean section? The above closure technique (a meme/fashion) is widespread fostered by copying peer practice, even though it differs from the original standard split two‐layer closure taught in the courses by the Royal College of Obstetricians and Gynaecologists. There are no studies or sound reasoning to support this current common technique.…”

“…2 The thick myometrial edges would be best approximated by a 'split two-layer suturing' without locking or excessive tightening in order to avoid ischaemia of the sutured myometrium. 2,3 The review 1 needs correction of a major error/oversight in the first paragraph of the 'Discussion' section where the main conclusion should read, 'Exclusion of decidua increased (not decreased) niche prevalence and impaired (not improved) healing ratio'. 1 More importantly, this main conclusion against the 'decidual exclusion' is wholly unreliable from the two studies 1 included.…”