Beyond the scar: a retrospective analysis of a rare subtype of abdominal wall endometriosis with muscle fascia invasion and its surgical implications

A total of 21 female patients diagnosed with abdominal wall endometriosis (AWE) were included in the study. The mean age was 32.2 years (range, 20–48 years). Comorbid conditions were present in 19% ( n  = 4) of patients, including diabetes mellitus and rheumatoid arthritis, while the remaining 81% ( n  = 17) had no significant medical history. A history of cesarean section was recorded in all patients, with 52.4% ( n  = 11) having undergone one cesarean delivery, 38% ( n  = 8) two, and 9.6% ( n  = 2) three. The mean interval between the last cesarean section and diagnosis of AWE was 4.6 years (range, 1–10 years). The average duration of symptoms prior to diagnosis was 19.3 months (range, 6–72 months). Most patients (76.2%, n  = 16) reported a cyclic painful mass at or near the cesarean incision, correlating with the menstrual cycle. On physical examination, palpable masses were most commonly located in the right iliac region (47.6%, n  = 10), followed by the left iliac region (33.4%, n  = 7), and the suprapubic area (19%, n  = 4). The average size of the mass on palpation ranged from 1 to 5 cm (mean: 2.8 cm). Radiological evaluation revealed lesion sizes ranging from 9 to 48 mm, with a mean diameter of 26.2 mm. Pelvic endometriosis was not detected in any patient during gynecologic evaluation. All patients underwent surgical excision. Wide local excision alone was performed in 57.1% ( n  = 12) of cases, while 42.9% ( n  = 9) required additional excision of the abdominal muscle fascia due to intraoperative evidence of fascial invasion. Among the 9 patients with fascial invasion, primary fascial repair was performed in 44.4% ( n  = 4), while polypropylene mesh reinforcement was required in 55.6% ( n  = 5). Histopathological examination confirmed endometriosis in all excised specimens. The mean follow-up period was 22 months (range, 12–60 months). Recurrence was observed in one patient (4.8%) at 14 months postoperatively. This case was presumed to represent multifocal disease and was successfully managed with repeat wide local excision. No further recurrence was observed during follow-up. A statistically significant positive correlation was found between the time elapsed since cesarean section and the duration of symptoms ( p  < 0.05, r  = 0.579), indicating that symptoms tended to persist or worsen over time. Additionally, a strong correlation was noted between lesion size on physical examination and corresponding radiologic measurements ( p  < 0.001, r  = 0.923). These findings are detailed in Tables  1 and 2 . Table 1 Clinical data, diagnostic methods, treatment and post operative outcomes No Age (years) Number of C/S Time after C/S (years) Symptom duration (months) Cycle painfulmass Location Radiologic diameter (mm) Surgical treatment Muscle fascia repair Outcome Follow-up duration (months) 1 38 1 4 15 + RIF 31 EME - H 42 2 48 1 8 9 + RIF 25 EME - H 13 3 34 3 5 21 + LIF 33 EME + MFR PR H 14 4 34 2 2 11 - LIF 11 EME - H 12 5 36 1 5 30 + RIF 20 EME - H 54 6 40 1 6 15 - RIF 9 EME - H 20 7 25 1 3 14 + LIF 28 EME + MFR PR H 46 8 26 1 2 12 + RIF 35 EME + MFR MR H 34 9 20 1 6 25 + SR 29 EME - R 60 10 33 1 10 72 - RIF 16 EME - H 24 11 29 2 8 30 + SR 38 EME + MFR MR H 48 12 28 2 1 13 - LIF 18 EME - H 52 13 32 2 4 10 + RIF 23 EME + MFR PR H 12 14 35 2 5 8 - LIF 16 EME - H 16 15 29 2 3 6 + RIF 25 EME - H 14 16 26 1 3 14 + LIF 28 EME + MFR PR H 56 17 30 1 2 12 + RIF 45 EME + MFR MR H 36 18 41 2 8 30 + SR 48 EME + MFR MR H 48 19 34 2 1 13 + LIF 18 EME + MFR - H 52 20 26 1 6 25 + SR 27 EME - H 58 21 34 3 5 21 + RIF 27 EME + MFR PR H 14 C/S  Cesarean sections, RIF  Right iliac fossa, LIF  Left iliac fossa, SR  Suprapupic region, EME  Extended mass excision, MFR  Muscle fascia repair, PR  Primary repair, MR  Mesh repair, H  Healing, R  Recurrence Table 2 Clinical features associated with abdominal wall endometriosis Clinical features Age Number of C/S’s Time after C/S’s Symptomduration Dimension in palpation Radiologicdimension Number of C/S’s (n:21) r 0.189 p 0.413 Time after C/S’s (years) r 0.318 −0.131 p 0.16 0.571 Symptomduration (months) r −0.006 −0.143 0.579** p 0.979 0.538 0.006 Dimension in palpation (cm) r −0.337 −0.005 0.03 0.253 p 0.135 0.982 0.898 0.268 Radiologicdimension(mm) r −0.254 −0.056 0.079 0.26 0.923** p 0.267 0.809 0.732 0.254 0 Follow-up duration (months) r −0.422 −0.405 0.006 0.532* 0.23 0.278 p 0.057 0.069 0.981 0.013 0.316 0.223 Statistically significant correlation: * p  < 0.05, ** p  < 0.001  C/S  Cesarean sections Clinical data, diagnostic methods, treatment and post operative outcomes C/S  Cesarean sections, RIF  Right iliac fossa, LIF  Left iliac fossa, SR  Suprapupic region, EME  Extended mass excision, MFR  Muscle fascia repair, PR  Primary repair, MR  Mesh repair, H  Healing, R  Recurrence Clinical features associated with abdominal wall endometriosis Statistically significant correlation: * p  < 0.05, ** p  < 0.001  C/S  Cesarean sections

This retrospective case series was conducted at a tertiary care center and included patients who underwent surgery for abdominal wall endometriosis (AWE) between January 2016 and December 2020. A total of 21 patients met the inclusion criteria and were analyzed. This study was approved by the Scientific Research Ethics Committee of Sancaktepe Prof. Dr. Ilhan Varank Training and Research Hospital, Istanbul Health Sciences University (Approval No: 2021/151, Date: 26/05/2021) and was carried out in accordance with the principles outlined in the Declaration of Helsinki. Written informed consent was obtained from all participants regarding both their treatment and the scientific use of their anonymized data. The study was designed and reported in compliance with the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) checklist for observational research. Patients were eligible if they presented with a painful, palpable anterior abdominal wall mass, underwent surgical resection with histopathologically confirmed endometriosis, had available preoperative imaging, and were followed for a minimum of 12 months postoperatively. Patients were excluded if their histopathologic diagnosis was inconsistent with endometriosis, if endometriosis was limited to pelvic structures without abdominal wall involvement, or if their medical records were incomplete. Relevant data were retrieved from the hospital’s electronic medical records. Variables included patient age, comorbidities, number and timing of previous cesarean sections, duration and cyclicity of symptoms, lesion location, size of the lesion on physical examination and imaging, type of surgical procedure performed, involvement of the abdominal muscle fascia, method of fascial repair (primary or mesh), histopathologic findings, follow-up duration, and recurrence status. All 21 patients underwent ultrasonography as the initial imaging modality, while preoperative MRI was performed in 9 patients and CT in 4 patients, based on clinical suspicion of deep tissue involvement or possible malignancy. All patients underwent clinical examination and abdominal ultrasonography. In selected cases, magnetic resonance imaging (MRI) or computed tomography (CT) was performed for further evaluation. MRI typically demonstrated well-demarcated, hyperintense nodules on T1-weighted sequences with variable enhancement, while ultrasonography revealed hypoechoic or heterogeneous soft-tissue lesions adjacent to the cesarean scar. Representative ultrasonographic and MRI images are provided in Fig.  1 . In nine patients with radiologic suspicion of soft tissue malignancy, ultrasound-guided core needle biopsy was performed prior to surgery to confirm the diagnosis. Prior to referral, most patients had been managed symptomatically with nonsteroidal anti-inflammatory drugs (NSAIDs). A few had received empirical hormonal therapy; however, persistent or progressive symptoms necessitated surgical intervention. Gynecologic consultation was also obtained for each patient, and all cases were confirmed as isolated AWE without radiologic or laparoscopic evidence of concurrent pelvic endometriosis. Fig. 1 Imaging of abdominal wall endometriosis; a  Ultrasonography, b  Magnetic resonance imaging Imaging of abdominal wall endometriosis; a  Ultrasonography, b  Magnetic resonance imaging All patients underwent surgery according to a standardized surgical protocol routinely followed in our center for abdominal wall endometriosis. This protocol included the following steps: Preoperative imaging and clinical evaluation to determine lesion location and assess fascial involvement. Preoperative ultrasound-guided skin marking in non-palpable cases. Wide local excision of the lesion, including the cesarean scar and at least 1 cm of surrounding healthy tissue. Intraoperative assessment for fascial invasion based on macroscopic signs such as firm adherence to underlying muscle, discoloration, and distortion of normal fascial planes. Extension of resection to include the fascia of the rectus abdominis and/or external oblique muscles in cases of confirmed invasion. Fascial repair using primary closure for defects < 3 cm, and reinforcement with synthetic polypropylene mesh (Prolene ® ) in the sublay position for larger or structurally weak defects. Preoperative imaging and clinical evaluation to determine lesion location and assess fascial involvement. Preoperative ultrasound-guided skin marking in non-palpable cases. Wide local excision of the lesion, including the cesarean scar and at least 1 cm of surrounding healthy tissue. Intraoperative assessment for fascial invasion based on macroscopic signs such as firm adherence to underlying muscle, discoloration, and distortion of normal fascial planes. Extension of resection to include the fascia of the rectus abdominis and/or external oblique muscles in cases of confirmed invasion. Fascial repair using primary closure for defects < 3 cm, and reinforcement with synthetic polypropylene mesh (Prolene ® ) in the sublay position for larger or structurally weak defects. Fascial invasion was further confirmed by histopathologic examination demonstrating ectopic endometrial glands and stroma within the fascial tissue. Intraoperative images including fascial defect exposure and repair techniques are shown in Fig.  2 . Fig. 2 Abdominal wall endometriosis; a Extended excision, b Fascia defect Abdominal wall endometriosis; a Extended excision, b Fascia defect Excised specimens were fixed in 10% buffered formalin, embedded in paraffin blocks, and sectioned into 5-micron slices. Hematoxylin and eosin (H&E) staining was performed on all samples. Diagnosis was confirmed by the presence of ectopic endometrial glands and stroma on microscopic examination. Figure  3 demonstrates representative macroscopic and microscopic images. Fig. 3 Abdominal wall endometriosis; a Macroscopy, b Microscopy (H&E x100) Abdominal wall endometriosis; a Macroscopy, b Microscopy (H&E x100) Patients were followed up at 1, 3, 6, and 12 months after surgery, and annually thereafter. Clinical evaluation during each visit focused on symptom recurrence, postoperative complications, and overall recovery. The mean follow-up duration was 22 months, ranging from 12 to 60 months. All statistical analyses were performed using IBM SPSS Statistics for Windows, Version 22.0 (IBM Corp., Armonk, NY, USA). The Kolmogorov–Smirnov test was used to assess the normality of distribution for continuous variables such as age, lesion size (palpation and radiologic), and symptom duration. As most variables were non-normally distributed, descriptive statistics were reported as median and interquartile range (IQR). Between-group comparisons (e.g., fascia invasion vs. no invasion) for continuous variables such as lesion size were analyzed using the Mann–Whitney U test. Chi-square or Fisher’s Exact test was used to assess associations between categorical variables such as the presence of cyclic pain and fascia involvement. The Spearman’s rank correlation coefficient was used to examine relationships between continuous variables, including the correlation between lesion size on palpation and radiologic measurement, and between time since cesarean section and symptom duration. A p-value of < 0.05 was considered statistically significant. Prior to data analysis, a power calculation was performed using G*Power 3.1 software. Based on a medium effect size (Cohen’s d = 0.80), an alpha error of 0.05, and a power of 80%, a minimum sample size of 8 patients was deemed sufficient. The inclusion of 21 patients ensured adequate statistical power [ 11 ].

In this study, we evaluated the clinical presentation, diagnostic process, surgical approach, and outcomes of patients with abdominal wall endometriosis, with a specific focus on muscle fascia involvement and reconstructive strategies. This study adds to the existing literature by presenting detailed data on fascia invasion, radiologic–clinical correlation, and decision-making in abdominal wall reconstruction, which remain insufficiently reported in prior case series. Our findings contribute to the limited body of literature on this rare but increasingly recognized form of extrapelvic endometriosis, particularly in the context of post-cesarean presentations. AWE most commonly occurs as a secondary form of endometriosis following gynecologic surgery, especially cesarean delivery. This aligns with the mechanical transplantation theory, which postulates that endometrial tissue is directly implanted into the abdominal wall during surgery [ 1 , 12 – 14 ]. Consistent with this mechanism, all patients in our series had a history of cesarean section, further reinforcing the well-established causal link. Although endometriosis is traditionally associated with pelvic involvement, isolated abdominal wall cases can occur independently. According to this theory, endometrial cells introduced during uterine incision may implant directly into the abdominal fascia or subcutaneous tissue, leading to localized disease without pelvic extension. Although pelvic endometriosis has been reported in approximately 12% of AWE cases in previous studies, none of the patients in our cohort demonstrated radiologic or gynecologic evidence of pelvic involvement [ 15 ]. This discrepancy may reflect referral patterns, the isolated nature of post-cesarean implantation, and the absence of symptoms prompting advanced pelvic imaging in this population. In our series, no patients had radiologic or laparoscopic evidence of concurrent pelvic endometriosis, a finding supported by other studies reporting isolated AWE following obstetric interventions [ 7 , 13 , 14 ]. The majority of our patients (76.2%) presented with cyclic pain and a palpable mass at the incision site, which is consistent with the classical clinical presentation of AWE. However, a significant subset (23.8%) exhibited atypical or non-cyclic symptoms. This observation aligns with previous reports suggesting that up to one-quarter of AWE cases may lack classic cyclicity, thus potentially delaying diagnosis [ 16 – 18 ]. These findings underscore the need for heightened clinical suspicion, especially in women with relevant surgical histories and nonspecific abdominal wall symptoms. A particularly notable aspect of this study is the high rate (42.9%) of abdominal muscle fascia invasion observed intraoperatively. This is higher than most published series, such as that by Sedhain et al. [ 19 ], which reported fascial involvement in approximately 29% of cases. In addition, when compared with the classification proposed by Wu et al. (Type I: 13.62%, Type II: 56.68%, Type III: 29.7%), our findings appear most consistent with Type II lesions, although the proportion in our study is slightly lower than their reported rate. This variation may be explained by institutional referral patterns, the small sample size, and the inclusion of patients with earlier-stage lesions [ 15 ]. The presence of fascia invasion significantly affects surgical planning, necessitating not only wider resection margins but also durable abdominal wall reconstruction. In our series, polypropylene mesh was used in patients with fascial defects ≥ 3 cm or compromised wall strength, based on our institutional protocol and supported by more recent literature [ 20 – 22 ]. Because subgroup numbers were small, mesh use should be interpreted as an institutional decision-making preference rather than a statistically derived result, and no comparative conclusions can be drawn regarding superiority of repair methods. No hernia formation was reported during a mean follow-up period of 22 months, supporting the safety of this approach. We also found a strong correlation between physical examination and radiologic measurements of lesion size ( r = 0.923, p < 0.001), suggesting that, in experienced hands, clinical assessment remains a valuable diagnostic tool. However, in 42.9% of cases, radiologic features mimicked soft tissue malignancy, prompting preoperative biopsy. Suspicious findings included irregular or ill-defined lesion margins, heterogeneous signal intensity on MRI, and apparent invasion of adjacent muscle or fascia. These features can overlap with soft tissue sarcoma or malignant transformation of endometriosis, although the latter is extremely rare. Although all lesions in this study were histopathologically confirmed as abdominal wall endometriosis, differential diagnoses such as desmoid tumors, lipomas, granulomas, and soft tissue sarcomas may present with similar clinical features. Regarding the relatively high proportion of suspicious cases (42.9%), this likely reflects a conservative diagnostic approach by radiologists rather than true suspicion of malignancy. In ambiguous cases, preoperative biopsy remains essential to exclude malignant transformation, which has been rarely reported in AWE, most commonly as clear cell or endometrioid carcinoma [ 23 , 24 ]. The average diagnostic delay in our study was 19.3 months, comparable to existing literature. Lukac et al. [ 25 ] highlighted that AWE is frequently misdiagnosed as benign conditions such as lipoma, sebaceous cyst, granuloma, or hernia, leading to prolonged symptom duration. Our findings support the need for increased awareness among both surgeons and gynecologists, particularly in the evaluation of post-cesarean abdominal wall masses. Only one patient (4.8%) experienced recurrence during follow-up, which was successfully managed with re-excision. This patient had originally undergone wide excision without overt fascial involvement, but recurrent symptoms developed 14 months postoperatively. Repeat imaging and surgical exploration revealed a small residual lesion in the subfascial plane, which was completely excised. No further recurrence was observed, suggesting possible multifocal disease or incomplete initial excision. This low recurrence rate supports the efficacy of our surgical strategy, which involved wide excision with at least a 1 cm margin of healthy tissue. Previous studies have identified inadequate surgical margins as a major risk factor for recurrence, and our results are consistent with this observation [ 8 , 26 ]. The strengths of our study include the exclusive inclusion of histopathologically confirmed cases, standardized surgical protocols, and a focus on long-term follow-up. Additionally, our analysis of fascia involvement and repair techniques adds clinically relevant data to a topic with limited coverage in current literature. Moreover, the study offers practical surgical insights by clarifying criteria for wide excision and mesh reinforcement, which may aid clinical decision-making in centers treating similar cases. Despite its contributions, our study has several limitations that must be acknowledged. First, the retrospective design inherently introduces the potential for selection and information bias. Clinical and radiologic assessments were performed based on existing medical records, and certain subjective variables, such as pain intensity or quality-of-life outcomes, could not be systematically evaluated. Second, the relatively small sample size may limit the statistical power of subgroup analyses, particularly regarding fascia involvement and recurrence. Third, the absence of a control group—such as patients managed conservatively or with medical therapy—precludes comparative evaluation of treatment modalities. Additionally, as a single-center study conducted in a tertiary care facility, our findings may reflect a referral bias and may not be generalizable to all healthcare settings. Finally, no long-term functional or aesthetic outcomes were systematically assessed, which limits conclusions regarding abdominal wall strength, cosmesis, and patient satisfaction after reconstruction. In conclusion, although rare, abdominal wall endometriosis should be considered in the differential diagnosis of anterior abdominal wall masses in women with a history of cesarean section. Diagnosis relies on a combination of clinical assessment, imaging, and histopathologic confirmation when necessary. Surgical treatment should consist of wide local excision, and in cases of fascial invasion, appropriate reconstruction—potentially involving mesh reinforcement according to defect size and institutional practice—should be planned. A multidisciplinary and preemptive surgical strategy appears to reduce recurrence and optimize long-term outcomes. The findings of this study highlight the importance of preoperative assessment, standardized excision criteria, and tailored reconstruction, thereby contributing novel and practical data to the growing evidence base on the surgical management of AWE.

Endometriosis is a chronic, estrogen-dependent inflammatory condition affecting approximately 10–15% of women of reproductive age, commonly involving pelvic organs but occasionally presenting in extrapelvic locations with diverse clinical challenges [ 1 , 2 ]. Extragenital endometriosis is a rare variant, most frequently reported in the gastrointestinal tract, urinary system, skin, and abdominal wall [ 3 , 4 ]. Abdominal wall endometriosis (AWE), particularly following cesarean section, manifests as a painful mass at or near the surgical scar. Its reported incidence ranges from 0.03% to 1.7% of all endometriosis cases [ 5 , 6 ]. The most frequently proposed pathophysiological mechanism for AWE involves secondary implantation of endometrial cells during obstetric or gynecologic procedures, such as cesarean delivery. These cells may be mechanically transferred to the surgical site and subsequently proliferate within the abdominal wall tissue [ 7 , 8 ]. However, in some cases, AWE invades the fascia of abdominal muscles, posing considerable surgical challenges. The extent of excision, repair of fascial defects, and the use of mesh remain controversial, as standardized surgical protocols have not yet been established [ 9 , 10 ]. Although current literature on AWE remains limited, recent studies have explored its diagnostic features through radiologic imaging, surgical techniques, and recurrence rates [ 5 , 8 ]. Nevertheless, data regarding muscle fascia involvement and its implications for surgical management and recurrence risk are still scarce. Long-term outcomes following fascial excision and mesh repair in AWE cases with muscle involvement remain unclear. This study aims to evaluate patients diagnosed with AWE who underwent surgical treatment following cesarean delivery, with particular emphasis on abdominal muscle fascia involvement, surgical approaches used, and long-term postoperative outcomes. By doing so, we aim to contribute meaningful data to the limited literature on the management of this rare but clinically significant entity.