Endometriosis of the uterine scar after cesarean section is like an invisible disease. Difficulties in diagnosis

Introduction

At present, there is a steady increase in the incidence of cesarean section (CS), which has consequently led to a rise in postoperative complications, one of the most significant being uterine scar dehiscence [1][2]. The prevalence of uterine scar defects is reported to range from 35.0% to 60.0% among women of reproductive age with a history of cesarean delivery [3][4][5][6].

In cases of uterine scar dehiscence accompanied by niche formation, the risk of serious obstetric complications is markedly elevated. These complications include uterine rupture at the site of the scar, cesarean scar pregnancy, placental implantation into the scar area, and cesarean scar endometriosis [7]. Clinically, such patients often present with abnormal uterine bleeding, chronic pelvic pain, or infertility [8][9][10].

One relatively rare but clinically significant cause of uterine scar dehiscence after a CS is endometriosis [11]. According to published studies, cesarean scar endometriosis accounts for approximately 0.42–4.0% of all endometriosis cases [12][13].

Endometriosis is a chronic disease characterized by the proliferation of endometrial-like tissue outside the uterine cavity, typically affecting women of reproductive age¹ [14][15].

Only a limited number of clinical cases of endometriosis involving a surgical uterine scar were described in the medical literature, making this form of the disease relatively rare. However, with the increasing prevalence of endometriosis among women of reproductive age and the growing number of cesarean deliveries, the incidence of postoperative scar endometriosis has risen accordingly. Data suggest that patients with two cesarean deliveries are more likely to develop scar endometriosis than those with a single CS [16].

A review of the literature indicates that cesarean delivery may serve as a triggering mechanism for the development of scar endometriosis due to iatrogenic implantation of endometrial cells into the surgical wound, followed by their proliferation and cystic transformation [17].

Scar endometriosis may be an independent factor contributing to the development of uterine scar dehiscence. Several authors have suggested that postoperative scar endometriosis can impair wound healing and predispose to the formation of a deficient uterine scar [18].

Importantly, the diagnosis of cesarean scar endometriosis remains challenging due to the lack of specific imaging features on ultrasound and magnetic resonance imaging (MRI). Hysteroscopy is considered the most informative diagnostic tool, revealing endometrial invaginations from the uterine cavity, irregular or eroded scar contours, and open-type endometriotic tracts containing characteristic “chocolate-like” fluid [19]. Nevertheless, in many cases, the diagnosis of scar endometriosis is made incidentally through histological examination [20].

The aim of this study was to analyze cases of surgical correction of uterine scar dehiscence following CS, to determine the incidence of cesarean scar endometriosis based on histopathological findings, and to evaluate the diagnostic efficacy of different imaging and endoscopic methods.

Materials and Methods

A retrospective analysis of 52 medical case histories was conducted over the period from January 2022 to December 2024.

Inclusion criteria: patients who underwent surgical correction of uterine scar dehiscence after a CS and were planning pregnancy.

Exclusion criteria: patients with uterine scars resulting from conservative myomectomy.

The following parameters were analyzed: patient age; the number of previous CSs; the presence of postoperative complications according to obstetric discharge summaries; presenting complaints at the time of hospital admission; results of pelvic ultrasound and MRI; findings from diagnostic hysteroscopy; histopathological reports.

Statistical analysis was performed using the R programming language within the RStudio environment, version 1.1.456 (open-source software available at https://github.com/rstudio/rstudio).

Correlations between dichotomous categorical variables were assessed using the contingency coefficient, and statistical significance was verified by the two-tailed Fisher’s exact test. For non-dichotomous categorical data, associations were evaluated using the Pearson and Tschuprow coefficients of contingency. A p-value < 0.05 was considered statistically significant.

Results

Analysis of patients’ medical histories revealed that the majority of participants (33; 63.5%) had undergone a single cesarean delivery, 12 patients (23.1%) had undergone two CSs, and 7 (13.4%) had experienced three CSs. The mean age of patients was 29.0 ± 2.3 years.

The frequency of postoperative complications after a CS is presented in Table 1.

When analyzing the patients’ complaints prior to planned surgical correction of the uterine scar, it was found that more than half of the women (36; 69.2%) reported no symptoms, while 10 patients (19.2%) complained of menstrual irregularities in the form of abnormal uterine bleeding (AUB), and 6 women (11.5%) reported localized pain in the scar area.

According to ultrasound (US) findings, cesarean scar endometriosis was diagnosed in 2 patients (3.8%), and according to MRI in 3 patients (5.8%). The mean preserved myometrial thickness above the apex of the scar was 1.5 ± 0.5 mm on ultrasound and 1.0 ± 0.5 mm on MRI.

Diagnostic hysteroscopy revealed features of scar endometriosis in 6 patients (11.6%). Histological examination of the excised uterine scar confirmed the presence of endometriosis in 15 cases (28.8%).

Thus, in 9 patients (17.3%), cesarean scar endometriosis was identified only by histological examination, whereas ultrasound, MRI, and hysteroscopy did not reveal this pathology. According to histological data, the presence of scar endometriosis was associated with the number of cesarean deliveries (Figure 1).

Given the high incidence of scar endometriosis detected postoperatively, a correlation analysis was performed between the patients’ clinical complaints and histological findings. The evaluated clinical manifestations included AUB and pain localized to the cesarean scar. Statistical significance was assessed using the two-tailed Fisher’s exact test (Table 2).

The analysis demonstrated statistically significant correlations between patient complaints of abnormal uterine bleeding and the presence of scar endometriosis confirmed by histology. In addition, a correlation was found between histologically confirmed scar endometriosis and the absence of clinical symptoms (Figure 2).

A further analysis was conducted to identify possible causes of scar endometriosis formation depending on post-cesarean complications, such as scar hematoma or postpartum endometritis. Correlation was calculated using the two-tailed Fisher’s exact test (Table 3).

The analysis revealed no statistically significant associations between postoperative complications following a CS and the development of scar endometriosis (Figure 3).

A correlation analysis was also performed between the diagnostic methods (hysteroscopy, ultrasound, and MRI) and histologically confirmed cases of scar endometriosis.

The statistical significance of the correlation coefficients was assessed using the two-tailed Fisher’s exact test (Table 4).

A statistically significant moderate correlation was established between the results of hysteroscopy and the histological findings of endometriosis (Figure 4). In addition, a statistically significant moderate correlation was identified when combined diagnostic approaches were used — specifically, hysteroscopy with pelvic MRI, hysteroscopy with pelvic ultrasound, and the combination of hysteroscopy, MRI, and ultrasound. Statistically significant correlations of moderate strength were found primarily when two or more diagnostic modalities were combined.

Nevertheless, histological examination remains the gold standard for confirming the diagnosis of “Cesarean scar endometriosis”.

A comparative evaluation of various diagnostic methods for cesarean scar endometriosis was performed using the following parameters: accuracy, sensitivity, and specificity (Table 5).

All methods demonstrated high accuracy and specificity, but low sensitivity, which is the key limiting factor in diagnosis. Only histological examination provided absolute diagnostic accuracy.

Discussion

The results of this study indicate that cesarean scar endometriosis remains a hidden and insufficiently studied condition. The underlying mechanisms of its development are still unclear and require further investigation.

In all patients diagnosed with scar endometriosis, there were no identifiable causal relationships with postoperative complications following a CS. This finding supports the polyetiological nature of endometriosis pathogenesis and makes it impossible to predict its development.

Our study confirmed a significant association between AUB — one of the key clinical complaints — and histologically verified cesarean scar endometriosis. This association suggests that the presence of AUB may serve as an indirect diagnostic indicator of this pathology. However, the observed correlation between the absence of symptoms and histologically confirmed endometriosis further emphasizes that cesarean scar endometriosis can also occur asymptomatically, regardless of its location or extent.

It was found that patients with three CSs were diagnosed with scar endometriosis more frequently than those with one or two cesarean deliveries, supporting the implantation theory of disease development.

A significant correlation between hysteroscopic and histological findings was also demonstrated, confirming that hysteroscopy is a valuable component of preconceptional evaluation in women with uterine scars for the diagnosis of scar dehiscence and possible endometriotic involvement.

The present analysis shows that ultrasound alone is not sufficient for diagnosing cesarean scar endometriosis due to its low sensitivity and limited diagnostic value. However, combining ultrasound with diagnostic hysteroscopy substantially improves detection rates. Therefore, a comprehensive diagnostic approach incorporating noninvasive imaging modalities (MRI and ultrasound) together with hysteroscopy is strongly recommended.

Statistical analysis revealed the high accuracy and specificity of the diagnostic methods employed, indicating that current tools can identify only the most evident cases of scar endometriosis. Nevertheless, their sensitivity did not exceed 47%, highlighting the limitations of imaging techniques. Histological examination remains the only method providing absolute diagnostic certainty.

A review of both domestic and international literature revealed a lack of studies addressing the diagnostic challenges of cesarean scar endometriosis, which precluded a comparative analysis of our findings with those of other researchers.

Conclusion

Cesarean scar endometriosis warrants particular clinical attention, as its diagnosis remains a challenging and unresolved task.

According to the Clinical Guidelines “Postoperative Uterine Scar Requiring Medical Care During Pregnancy, Delivery, and the Postpartum Period”, approved by the Ministry of Health of the Russian Federation on September 6, 2024, ultrasound examination on days 7–9 of the menstrual cycle is recommended for women at risk of developing a clinically significant uterine scar niche. Despite the high resolution of modern ultrasound devices, this method has demonstrated low sensitivity in detecting cesarean scar endometriosis. As additional diagnostic tools, MRI and diagnostic hysteroscopy should be employed.

A combination of diagnostic modalities used during preconception assessment can enhance the detection rate of cesarean scar endometriosis and enable timely surgical management of the identified pathology.

The mainstay of diagnosis remains histopathological examination. Histological evaluation of excised scar tissue should be mandatory as histological confirmation of endometriosis allows clinicians to initiate targeted therapy aimed at reducing the risk of recurrence.

In conclusion, further clinical and morphological research is necessary to establish clear diagnostic criteria and to elucidate the etiopathogenic mechanisms underlying this rare but clinically significant condition.