Uterine cystic adenomyoma arising from cesarean scar diverticulum: a case report and literature review

A 37-year-old woman, gravida 3 para 2 abortus 1, presented with prolonged menstrual bleeding and increased menstrual volume for over 5 years after her last cesarean delivery in 2019. She reported a menstrual period of 10–15 days and a cycle of 25–30 days. The patient didn’t experience fever and periodic abdominal pain. During the last decade, she underwent one medical abortion, two cesarean section deliveries, and one myomectomy. The current gynecological examination found a pelvic mass with a diameter of around 5 cm at the anterior uterus. Lab tests showed a negative pregnancy test and mild anemia, with a hemoglobin level of 96 g/L, and the cancer antigen 125, carbohydrate antigen 19 − 9, and human epididymis protein 4 were within normal limits. In 2021, the patient visited our hospital due to the prolonged menstruation. Transvaginal sonography (TVS) examination revealed a small cesarean scar diverticulum (CSD) at the anterior wall of lower uterine segment (LUS) (Fig.  1 A). She was recommended to monitor the symptoms without intervention. The current TVS in this visit in 2024 found a heterogeneously hypoechoic mass at the anterior LUS, with the size of 5 × 4 cm, which was measured by the largest dimensions of the length and width. Interestingly, the lesion was well-demarcated from the adjacent myometrium with the thickness of 8 mm. It penetrated the entire thickness of the uterine wall, protruded outside of the uterus, and established a direct communication with the endometrial cavity. Doppler ultrasound showed the ring-like blood flow signals surrounding the mass (Fig.  1 B, C). The sonographic appearances were not in favor of a typical CSD, which is normally characterized with thin muscles surrounding the niche. Overall, the origin of the mass at the site of the prior cesarean scar was primarily identified on TVS. While the specific pathology remained unclear, the sonographic features were not indicative of malignancy. This assessment was further supported by normal serum tumor marker levels. Following multidisciplinary discussion, we proceeded with a combined hysteroscopic and laparoscopic approach without preoperative MRI given the strong evidence for a benign lesion. Fig. 1 Presurgical TVS examinations. A A previous TVS in 2021 found a small CSD without existence of a mass (yellow arrow). B The presurgical TVS examination in 2024 showed a thick-wall (8 mm) and heterogeneously hypoechoic mass (yellow arrow) at the anterior LUS. The mass communicated with the uterine cavity and was well circumscribed from the myometrium, mostly protruding outside the uterus. C Doppler ultrasound showed the ring-like blood flow signals surrounding the mass (yellow arrow). M: mass, CX: cervix, UT: uterus Presurgical TVS examinations. A A previous TVS in 2021 found a small CSD without existence of a mass (yellow arrow). B The presurgical TVS examination in 2024 showed a thick-wall (8 mm) and heterogeneously hypoechoic mass (yellow arrow) at the anterior LUS. The mass communicated with the uterine cavity and was well circumscribed from the myometrium, mostly protruding outside the uterus. C Doppler ultrasound showed the ring-like blood flow signals surrounding the mass (yellow arrow). M: mass, CX: cervix, UT: uterus Hysteroscopic exploration revealed a normal cervix, uterine cavity, and bilateral fallopian tube ostia. A diverticulum of around 5 × 4 cm associated with the previous cesarean scar was identified, connected to the uterine cavity and filled with viscous chocolate-like fluid (Fig.  2 A). The bloody fluid was removed. Using a combination of hysteroscopic light source and laparoscopic camera, a positive transillumination test in the lower uterine segment confirmed the presence of the CSD (Fig.  2 B). Bilateral ovaries and fallopian tubes appeared normal. Subsequently, the overlying peritoneum was carefully dissected using an ultrasonic scalpel, exposing a protruding mass measuring approximately 5 × 4 cm. The lesion was well-demarcated from the adjacent myometrium and penetrated the entire thickness of the uterine wall, establishing a direct communication with the endometrial cavity. The lesion was excised intact, and the CSD in the uterine wall was subsequently repaired (Fig.  2 C). Fig. 2 The combination of hysteroscopic and laparoscopic operation. A Hysteroscopy showed a diverticulum after removing the blood. B Simultaneous use of hysteroscopy and laparoscopy identified the presence of a huge CSD. C The mass was removed and the CSD was repaired (yellow arrow) The combination of hysteroscopic and laparoscopic operation. A Hysteroscopy showed a diverticulum after removing the blood. B Simultaneous use of hysteroscopy and laparoscopy identified the presence of a huge CSD. C The mass was removed and the CSD was repaired (yellow arrow) Postoperative pathology revealed multiple endometrium tissues in the myometrium accompanied by diffuse smooth muscular hyperplasia (Fig.  3 ), which were in accordance with uterine cystic adenomyoma (UCA). The final clinical diagnosis was a CSD accompanied by UCA. The patient’s menstrual condition improved after surgery. Fig. 3 Postoperative pathology. A - B Pathological findings showed the mass consisted of cystic adenomyosis lesions (yellow arrow) and smooth muscle hyperplasia (yellow arrowhead). C The significant smooth muscle hyperplasia (yellow arrowhead) at the outer layer of the CSD, in favor of the sonographic appearances of thick wall Postoperative pathology. A - B Pathological findings showed the mass consisted of cystic adenomyosis lesions (yellow arrow) and smooth muscle hyperplasia (yellow arrowhead). C The significant smooth muscle hyperplasia (yellow arrowhead) at the outer layer of the CSD, in favor of the sonographic appearances of thick wall

Uterine diverticulum refers to an outpouching or sac-like protrusion of the uterine wall. It is also known as “uterine defect”, “uterine dehiscence”, “isthmocele”, “niche”, “pouch,” or “sacculation” in the literatures. Uterine diverticulum can be classified into congenital- and secondary- uterine diverticulum. Congenital uterine diverticulum is a rare anomaly characterized by a localized outpouching of the uterine wall that is present at birth. It is typically caused by abnormal embryological development of the Müllerian ducts. Secondary uterine diverticulum refers to an acquired outpouching of the uterine wall. The most common subtype is CSD, but it can also occur after other pelvic surgeries, such as myomectomy [ 3 , 4 ]. According to the European Niche Taskforce in 2019, CSD is defined as an indentation at the site of previous cesarean section scar with a depth of at least 2 mm measured by TVS [ 5 ]. On ultrasound, CSD appears as an anechoic or hypoechoic structure at the site of the previous cesarean section. Histologically, the CSD consists of smooth muscles and endometrium, which connects to the uterine cavity. Possible factors that could contribute to the CSD development include a very low incision, inadequate suturing technique during closure of the uterine scar, surgical interventions that increase inflammatory microenvironment, and patient-related factors that affect wound healing [ 6 ]. CSD can cause abnormal uterine bleeding, chronic pelvic pain, cesarean scar pregnancy, and infertility, but CSD-associated pelvic mass is very rare. In this study, we reported an extreme rare case of UCA arising from CSD. UCA is an uncommon variant of adenomyoma characterized with a circumscribed cavitated endometrial gland and stroma within the myometrium. The cysts contain chocolate-like fluid, usually greater than 10 mm in diameter [ 7 ]. This distinguishes it from a simple adenomyoma or adenomyosis, which typically do not present with cystic components. UCA can also be classified as congenital UCA and secondary UCA. The congenital UCA is associated with abnormal embryological development of the Müllerian ducts. In this case report, the patient didn’t have any adenomyoma at her TVS examination in 2021 while was found a UCA in 2024 after multiple uterine operations. We presume that UCA arising from CSD might result from the incomplete wound healing after operations rather than Müllerian ducts anomalies. Furthermore, the patient’s uterus retropositon could also increase the tension at the scar and impair incision healing, promoting the formation of CSD. Suturing technique affected the wound healing as well. According to latest research, the chronic inflammatory microenvironment at the wound site should also be taken into consideration. The increased smooth muscle proliferation [ 8 ] and elevated inflammatory cytokines, such as IL-1α, IL-1β, IL-6, IL-8, SDF-1α, and TNF-α, might be associated with the activation of fibroblast, and the proliferation and migration of endometrium [ 9 ]. However, the etiology and pathogenesis of a mass occurring at CSD need further investigation. Additionally, a few cases of a pelvic mass arising from CSD, which are likely to cause misdiagnosis, have been reported in recent years, including abscess [ 10 – 12 ], endometriosis cyst [ 13 , 14 ], and fibroid [ 15 ]. Endometrial adenosarcoma [ 16 ] and high-grade endometrial stromal sarcoma [ 17 ] with a size of 5 mm and 10 mm have also been found at CSD. In 2022 and 2023, UCA arising from CSD were reported respectively [ 18 , 19 ]. To our best knowledge, our case is the third documentation of CSD accompanied by UCA. The details of mass-forming lesions arising from congenital uterine diverticulum (14 cases) and CSD (10 cases) were summarized in Fig.  4 ; Tables  1 and 2 . Fig. 4 Diseases distribution of congenital uterine diverticulum- ( A ) and CSD- ( B ) associated uterine diverticulum Diseases distribution of congenital uterine diverticulum- ( A ) and CSD- ( B ) associated uterine diverticulum Table 1 Characteristics of congenital uterine diverticulum presenting as pelvic mass (es). G: gravidity; P: parity; /: not mentioned; ?: unclear Study Age Clinical presentation G/ P Uterine surgery Mass site Mass size (cm) Primary diagnosis Final diagnosis Treatment Outcome Bennet 1937 [ 20 ] 24 Lower abdominal pain 0/0 No Right lateral uterine wall 2.5 × 2 × 1.5 Fallopian pregnancy Acute uterine diverticulitis Total abdominal hysterectomy Premenstrual pain Engle 1984 [ 21 ] 34 Abdominal pain, postmenstrual bleeding 0/0 No Posterior uterine wall 7.5 / Infected uterine diverticulum Total abdominal hysterectomy / Seoud 2002 [ 22 ] 31 Menorrhagia, primary infertility 0/0 No Cervix 5 / Congenital cervical diverticulum Ovarian hyperstimulation and intrauterine insemination Pregnancy Umezaki 2004 [ 23 ] 41 Abdominal distension, vaginal bleeding, frequent urinary, fever 4/3 Induced abortion Posterior uterine wall 20 Infected degenerate leiomyoma Infected cervical diverticulum Laparotomy / Coronado 2008 [ 24 ] 29 Menorrhagia, intermenstrual spotting 0/0 No Left cervix 5.9 × 5.4 / Uterine cervical diverticulum Diverticulum excision Asymptomatic Rajiah 2009 [ 25 ] 20 Asymptomatic 1/0 No Left posterior cervix 6.5 Bicornuate uterus Congenital uterine diverticulum Cesarean delivery without repairing the diverticulum Asymptomatic Chufal 2012 [ 26 ] 45 Severe lower abdominal pain 2/2 No Left uterine isthmus 18 × 16 × 10 Twisted ovarian cyst Uterine cervical diverticulum Total abdominal hysterectomy / Tanha 2018 [ 27 ] 37 Menorrhagia, secondary infertility 1/1 No Between internal and external cervix OS 3.5 × 2.2 Asherman’s syndrome Uterine cervical diverticulum Drainage of blood clot / Noguchi 2019 [ 28 ] 37 Abdominal distension and pain 0/0 No Cervix An adult head-sized A fibroid at bicornuate uterus A leiomyoma at uterine cervical diverticulum Fibroid resection and cervicoplasty Asymptomatic Gojayev 2019 [ 29 ] 30 Multiple pelvic infection 2/1 Cesarean delivery Cervix 11 × 7 × 14 Uterine hematometra; pelvic abscess; degenerative leiomyoma Congenital uterine cervical diverticulum Removal of pelvic mass Asymptomatic Tanaka 2020 [ 30 ] 32 Infertility 0/0 No Right cervix 5 A cyst unrelated to infertility Congenial uterine diverticulum Diverticulum resection Pregnancy and vaginal delivery Akashi 2021 [ 31 ] 25 Uterine anomaly 1/0 No Posterior uterine isthmus 18 Leiomyoma Leiomyoma at uterine diverticulum Laparotomy Asymptomatic De 2023 [ 32 ] 44 Abdominopelvic mass, pelvic pain, intermenstrual bleeding ?/4 No Cervix 18 × 15 × 9 Uterine fibroid Cervical fibroid, diverticulitis Panhysteroctomy / Nishiuchi 2024 [ 33 ] 40s Lower abdominal pain, fever 3/2 No Anterior uterine wall 13.2 × 12 × 15.5 Endometriotic cyst of ovary with infection Congenital uterine diverticulum Total hysterectomy / Characteristics of congenital uterine diverticulum presenting as pelvic mass (es). G: gravidity; P: parity; /: not mentioned; ?: unclear Engle 1984 [ 21 ] Seoud 2002 [ 22 ] Coronado 2008 [ 24 ] Rajiah 2009 [ 25 ] Chufal 2012 [ 26 ] Tanha 2018 [ 27 ] Menorrhagia, secondary infertility Gojayev 2019 [ 29 ] Tanaka 2020 [ 30 ] Akashi 2021 [ 31 ] De 2023 [ 32 ] Nishiuchi 2024 [ 33 ] Endometriotic cyst of ovary with infection Table 2 Characteristics of mass-forming lesion arising from CSD. G: gravidity; P: parity; /: not mentioned Study Age Clinical presentation G/ P Uterine surgery Mass site Mass size (cm) Primary diagnosis Final diagnosis Treatment Outcome Garcia 2009 [ 10 ] 36 Hypogastric pain 1/1 Cesarean delivery Anterior uterine wall 24 × 19 × 30 / CSD abscess Antibiotics, abscess aspiration, hysterolaparoscopic fulguration Asymptomatic Ou 2011 [ 11 ] 41 Intermittent fever, lower abdominal pain 2/2 Two cesarean deliveries Lower anterior uterine wall 5 × 6 × 9 An infected uterine tumor with possibility of malignant change An infected CSD Total abdominal hysterectomy Asymptomatic Taguchi 2012 [ 12 ] 44 Abdominal pain, fever, and uterine bleeding 1/1 Cesarean delivery Lower anterior uterine segment 12 × 10 × 10 Cesarean scar abscess Cesarean scar abscess Total abdominal hysterectomy / Masuda 2015 [ 34 ] 43 Secondary infertility, postmenstrual brown discharge 2/1 Cesarean delivery Right anterior uterine / Diverticular hernia CSD Hysteroscopically removed CSD Postmenstrual discharge stopped; cesarean delivery at 37 weeks Chen 2021 [ 13 ] 40 Menorrhagia 4/2 Two cesarean deliveries Isthmus Two masses: 3 and 5 / Plantation of endometriotic lesions at the CSD Removal of masses Menstrual condition improved Lee 2022 [ 35 ] 45 Heavy vaginal bleeding 4/2 Two cesarean deliveries Anterior wall of the lower uterine segment 0.5 × 0.5 / High-grade endometrial stromal sarcoma at CSD Hysterectomy with bilateral salpingo-oophorectomy, aortic and pelvic lymph nodes dissection + hormonal therapy / Xu 2022 [ 14 ] 40 Menstrual irregularity / Two cesarean deliveries Anterior uterine wall 8.06 × 6.23 × 3.66 / Endometriosis cysts at CSD Resection of the endometriotic cyst Recurrence-free Sethupathy 2023 [ 15 ] 46 Dysmenorrhea, menorrhagia, intermenstrual bleeding / Two cesarean deliveries Right lateral site of the cesarean scar 7.3 × 3.4 / CSD with degenerated broad ligament fibroid Incision and repair of the CSD / Teodor 2024 [ 36 ] 35 Acute pelvic pain / Two cesarean deliveries Vesicouterine pouch 4 Uterovesical/uteroperitoneal fistula; pelvic abscess; bladder endometriosis CSD abscess Total hysterectomy, bilateral salpingectomy and partial cystectomy Asymptomatic Han 2024 [ 16 ] 44 Irregular vaginal bleeding / Cesarean delivery Junction of the corpus uteri and cervix 1.2 × 0.9 × 1.3 / Endometrial adenosarcoma Hysterectomy and salpingo- oophorectomy Recurrence-free Characteristics of mass-forming lesion arising from CSD. G: gravidity; P: parity; /: not mentioned Garcia 2009 [ 10 ] Ou 2011 [ 11 ] Taguchi 2012 [ 12 ] Masuda 2015 [ 34 ] Chen 2021 [ 13 ] Lee 2022 [ 35 ] Xu 2022 [ 14 ] Sethupathy 2023 [ 15 ] Teodor 2024 [ 36 ] Han 2024 [ 16 ] Hysterectomy and salpingo- oophorectomy Both congenital uterine diverticulum- and CSD-associated pelvic masses can present with lower abdominal pain, dysmenorrhea, menorrhagia, abnormal uterine bleeding. The presence of uterine surgery history, particularly a cesarean section scar, is very helpful for differential diagnosis. However, in Table  1 , a woman with a history of cesarean delivery presented with a pelvic mass arising from congenital cervical diverticulum. It reminds gynecologists that identifying the correct origin site of the mass(es) is of great significance. Medical imaging, such as TVS and MRI, can help confirm the mass site and evaluate its relationship with surrounding tissues. A mass at CSD should locate at the anterior wall of LUS, while in congenital uterine diverticulum cases, the masses usually occur at the isthmus and cervix, which are anatomically weak sites to develop a diverticulum. However, there could occur masses in different types and sizes, which causes a diagnostic dilemma. As shown in Tables  1 and 2 , uterine diverticulum could present as pelvic mass and be pre-surgically misdiagnosed as fallopian pregnancy, infected degenerate leiomyoma, bicornuate uterus, twisted ovarian cyst, Asherman’s syndrome, uterine hematometra, endometriotic cyst of ovary with infection, and uterovesical/uteroperitoneal fistula. In most cases, hysteroscopy and laparoscopy was crucial for final diagnosis. In addition, the immunohistochemical marker CD10 can be beneficial to identify the origin of uterine diverticula. The epithelial lining of mesonephric remnants and the resulting lesions exhibit CD10 positive, while the cervical and endometrial lining epithelium show negative staining, with the stroma demonstrating positive CD10 expression [ 37 ]. Accurate diagnosis plays an important role for proper management of uterine diverticulum. TVS and MRI are utilized as powerful tools to clarify the location of the mass, its relationship with the diverticulum, and the possible types (infection/benignity/malignancy). The connecting channel to uterine cavity and location at anterior LUS found by TVS or MRI, and the history of cesarean deliveries are useful clues for diagnosis. The gynecologists should be aware that CSD can have scar defects of unusual shapes and features, as well as complicated with mass-forming lesions. Additionally, the likelihood of malignancy from a mass even with very small size cannot be excluded. In previous publications [ 16 , 17 ], a mass of around 5 mm and a mass of 12 mm were proven to be high-grade endometrial stromal sarcoma and endometrial adenosarcoma, respectively. The decision to treat CSD-associated mass depends on factors like symptoms, pregnancy plans, mass type and size. For asymptomatic cases with no pregnancy plans, conservative management through clinical observation is often recommended. For symptomatic patients, surgery, including hysteroscopic approach, laparoscopic approach, vaginal approach, and laparotomy, will often improve virginal bleeding and subfertility. Some cases with the malignant mass, surgery combining other therapies (e.g., chemotherapy and radiotherapy) may be needed. Each approach carries specific risks, such as infections, bowel/bladder injury, hemorrhage, and reoccurrence. The choice of treatment depends on individual circumstances and preferences. In summary, this work presented a rare case of CSD-associated UCA and extended our contribution by conducting a comprehensive review of 24 studies documenting various mass-forming pathologies at the CSD site. This synthesis allows us to present a broader perspective on the etiology, pathological mechanisms, and differential diagnosis of masses arising in cesarean scars, providing an educational resource that enhances clinical awareness, outlines a strategic approach for differential diagnosis, and underscores the need for individualized therapy based on patient presentation and reproductive plans.

In patients with a prior cesarean section, a mass in the lower uterine segment, especially with a cavity connection, should raise suspicion for a cesarean scar diverticulum (CSD)-associated lesion. When transvaginal ultrasound is inclusive, pelvic MRI serves as a diagnostic adjunct. For management, the combined hysteroscopic-laparoscopic approach allows for precise excision of the mass and concurrent repair of the CSD defect in a single procedure. Future efforts should focus on refining the classification of these masses and standardizing management procedures to optimize symptomatic and reproductive outcomes.

The broadly rising cesarean section delivery rate, evaluated as 25–50% [ 1 ], has increased the possibility of cesarean scar diverticulum (CSD), which grows to 61% after one cesarean section and up to 100% after at least three times cesarean section [ 1 , 2 ]. CSD is characterized by a discontinuity or defect of myometrium at the previous cesarean section scar. In a subgroup, it can cause a series of gynecological, reproductive, and obstetrical symptoms, such as abnormal uterine bleeding, pelvic pain, infertility, and CSD pregnancy. The pelvic masses arising from CSD have rarely been documented. In this setting, mass-forming lesions associated with CSD are challenging for accurate diagnosis and further effective management. Herein, this article will present an extremely rare case of a cystic adenomyoma arising from CSD and review a series of rare cases, including abscess, leiomyoma, endometriosis cyst, endometrial adenosarcoma, and high-grade endometrial stromal sarcoma, that occur at CSD. This study aims to deepen the understanding of the early identification, differential diagnosis, and treatments of mass-forming lesions associated with CSD.