Accessory cavitated uterine malformation in a perimenopausal woman: Case report and literature review

Abstract

Accessory cavitated uterine malformation is a rare congenital anomaly of Müllerian duct development that typically affects younger women of reproductive age. The most common symptoms include chronic cyclic pelvic pain and severe dysmenorrhea, although diagnosis is frequently delayed owing to its rarity, multiple differential diagnoses, and low patient awareness. This report describes the case of a perimenopausal woman with accessory cavitated uterine malformation. The patient exhibited a palpable mass in the right lower abdomen without notable chronic pelvic pain or dysmenorrhea. It was initially misdiagnosed as an adnexal cyst in the right region based on ultrasound imaging, and laparoscopic exploration revealed a mass in the uterine corpus, leading to a revised diagnosis of accessory cavitated uterine malformation, which was confirmed through intraoperative findings and histopathological examination. The postoperative outcomes were favorable. This case underscores the diagnostic challenges of accessory cavitated uterine malformation, given the limited research on its pathogenesis and the absence of distinctive diagnostic markers. Imaging and histopathology are essential for an accurate diagnosis. Surgical intervention, especially laparoscopy, remains the preferred treatment, with excision typically resulting in a favorable postoperative prognosis.

Introduction

Accessory cavitated uterine malformation (ACUM) is an uncommon congenital anomaly of the Müllerian duct. ACUM was first described by Cullen in 1908, who classified it as an adenomyoma. ¹ Since then, various terms have been used to describe this condition. In 2010, Acien et al. ² reviewed its clinical characteristics and proposed the term “ACUM” to better define it. ACUM typically presents as a noncommunicating accessory mass within the myometrium or broad ligament, often near the insertion of the round ligament. ACUMs are cystic lesions lined by functional endometrial tissue.

Patients with ACUM generally have a normally developed uterus, fallopian tubes, and ovaries. However, they often experience progressively worsening dysmenorrhea without other specific symptoms, leading to frequent misdiagnosis, most commonly as cystic adenomyosis.^2,3 Due to the limited understanding of ACUM, it is frequently misdiagnosed or diagnosed late, resulting in prolonged symptoms of dysmenorrhea, pelvic pain, and lower abdominal pain, all of which significantly impact the quality of life.

Recently proposed theories suggest that ACUM may be associated with either the persistent presence of Müllerian duct tissue near the round ligament attachment or dysfunction of the gubernaculum, which ultimately forms the round ligament.^3,4 Periodic bleeding causes blood accumulation within the closed ACUM cavity, leading to increased intraluminal pressure and the accompanying clinical symptoms.

In this study, we reviewed a case of ACUM, which was found in a perimenopausal woman and treated at the Affiliated Hospital of Shandong Second Medical University in Weifang, Shandong, China. Additionally, we examined the relevant literature to enhance diagnostic and therapeutic approaches for ACUM.

Case report

A 45-year-old woman presented with a palpable mass in her right lower abdomen that had been present for approximately 1 month. The mass measured approximately 10 cm in diameter and was mobile and nontender upon palpation. She reported regular menstrual cycles since menarche at the age of 14 years, with a cycle length of 30 days, menstrual duration of 5–7 days, moderate blood flow of reddish color, and no significant dysmenorrhea. Her obstetric history included four spontaneous conceptions, two of which culminated in cesarean deliveries and two in medical abortions due to unintended pregnancies. The patient denied any history of mental illness, genetic disorders, or familial diseases.

Concerned about the nature of the mass, she sought medical evaluation at our hospital for the first time in October 2023, where a bimanual examination revealed a cystic mass of approximately 10 cm in diameter on the right anterior side of the uterus, with defined borders, limited mobility, and mild tenderness on pressure. A transvaginal color Doppler ultrasound was subsequently performed, showing a cystic echo measuring approximately 11.4 × 5.7 × 5.8 cm in the right adnexal region, with septations visible within the cyst (Figure 1). Color Doppler flow imaging with pulse wave analysis showed no abnormal blood flow or spectral pattern. Based on ultrasound findings, the mass was classified as The Ovarian-Adnexal Reporting and Data System (O-RADS) grade 3. ⁵

Figure 1.

Representative transvaginal ultrasound of a 45-year-old woman in this case. (a) A cystic echo was observed in the right adnexal region, with clear borders, regular morphology, and poor acoustic transparency, displaying a ground-glass appearance, and potential septations inside and (b) The anechoic area is closely associated with the right wall of the uterus.

During a 3-h laparoscopic exploration, a bulging mass was observed on the right side of the uterine corpus, located between the right round ligament and the fallopian tube, extending toward the lower portion of the broad ligament (Figure 2(a)). The mass measured approximately 11 cm in diameter. The overlying myometrial layer was incised via monopolar cautery, revealing the mass with a smooth surface (Figure 2(b)), which was carefully dissected using hemostatic forceps and monopolar cautery. During dissection, the cyst ruptured, releasing a thin, chocolate-colored fluid (Figure 2(c)), which was thoroughly aspirated. Intraoperative frozen-section analysis of the specimen (Figure 2(d)) indicated that the mass was consistent with adenomyosis with cystic changes. The cyst cavity and uterine incision were meticulously sutured post-extraction. The ovaries and fallopian tubes on both sides were of normal size and morphology (Figure 2(a), (e), (f)).

Figure 2.

Intraoperative findings. (a) The cyst was located between the right round ligament and the oviduct, extending to the lower end of the broad ligament. (b) The right ovary appeared normal in morphology. (c) The mass had a smooth surface. (d) The complete cystic specimen was sent for intraoperative frozen-section analysis. (e) The cyst ruptured spontaneously during the surgery, releasing chocolate-like fluid and (f) the uterus returned to its normal condition after the cyst was excised. CY: cyst; UT: uterus; OV: ovary; OD: oviduct; RL: round ligament.

Histopathological examination revealed that the inner cavity was lined with endometrial epithelium, with both glands and stromal tissue present (Figure 3). Based on these laparoscopic and histopathological findings, a final diagnosis of ACUM was made. Until the time of preparing this case report, the patient has been monitored for 11 months postoperatively, showing regular menstrual cycles and no recurrence of the mass, as confirmed via transvaginal ultrasound. Additionally, the patient was satisfied with the treatment.

Figure 3.

Histopathological examination imaging. (a) The cyst appears relatively large under low magnification and (b, c) smooth muscle tissue is observed within the cyst wall, and endometrial-like tissue, including glands and stroma (red arrows), is visible on the inner side of the cyst wall. SMT: smooth muscle tissue.

Written informed consent was obtained from the patient for treatment, use of clinical data for research, and publication of individual medical details and accompanying images. We have deidentified all patient details in the report. This study conforms to the Case Report (CARE) guidelines. ⁶

Discussion

ACUM is a clinically elusive obstructive congenital anomaly characterized by a normally developed, functional uterus with an accessory cavity lined with endometrial tissue. ⁷ Due to its rarity, most available studies are individual case reports, and ACUM remains poorly understood, contributing to frequent misdiagnosis and the inability to accurately determine its incidence. The case reported by Oliver published in 1912 is retrospectively regarded the earliest confirmed case of ACUM. ⁸ Oliver described a globular, closed cystic cavity with thick walls, containing chocolate-colored fluid and tissue resembling the stroma of normal endometrium.

It was not until 2010 that Acien formally distinguished ACUM as a separate entity. By comparing ACUM with true uterine adenomyomas, Acien et al. concluded that although they exhibit some similarities, ACUM has distinct characteristics and likely originates from Müllerian duct developmental anomalies. ² Before this classification, ACUM was described using various terms, such as juvenile or isolated cystic adenomyoma, uterus-like mass, accessory uterine cavity, and adenomyotic cyst or cystic adenomyosis. ⁹

Pathogenesis

Three primary theories have been proposed to explain the histogenesis of ACUM: (a) the congenital anomaly theory; (b) the heterotopia theory; and (c) the metaplasia theory. ¹⁰ The congenital anomaly theory is the most widely accepted and can be divided into theories of Müllerian duct malformations and round ligament dysplasia. ² According to this theory, residual Müllerian duct tissue may develop into structures resembling the primary uterus or its appendages, potentially giving rise to ACUM. However, in numerous reported cases, ACUM was situated at or near the attachment site of the round ligament at the uterine horn. This anatomical observation has led to the hypothesis that ACUM formation may be linked to abnormal round ligament attachment or dysfunction of the female gubernaculum during embryonic development.^3,4

Clinical manifestation

Patient demographics

Available case reports indicate that ACUM typically occurs during the childbearing age, with no documented cases among premenarcheal or postmenopausal individuals. In the cohort studied by Takeuchi et al., ¹¹ none of the nine ACUM patients were older than 30 years, whereas Naftalin et al. ¹² reported a median age of 29.2 years among 20 ACUM cases. Dekkiche et al. ⁹ found a mean age of 22 years, with a range of 17–35 years, across nine ACUM patients. A recent case report from China described a patient who first presented at the age of 37 years and was diagnosed and treated at 47 years, during the perimenopausal period, suggesting a significant diagnostic delay. The current case, diagnosed at 45 years, is notably older than most reported cases, potentially providing new insights into the onset and progression of ACUM in older patients. This rarely reported age of onset may provide valuable insight into future research on ACUM timing and presentation.

Lesion characteristics

In a study encompassing 20 ACUM cases, ¹² the mean external diameter of ACUM lesions was reported to be 22.8 mm (95% confidence interval (CI): 20.9–24.8 mm), while the mean internal diameter was 14.1 mm (95% CI: 12.2–16.1 mm). More recently, a 2023 study summarized data from 88 ACUM patients, showing an increased mean lesion size of approximately 3.4 cm. ⁹ Consistent with these findings, Fei et al. ¹³ reported a mean maximal diameter of 3.0 ± 1.0 cm across 11 ACUM cases in 2024. Additionally, a study analyzing 109 cases found that ACUM lesion size tends to increase with patient age, likely due to accumulative intracapsular bleeding associated with menstrual flow. ¹⁴ In our case report, the cyst diameter measured approximately 11 cm, significantly exceeding the documented ones in existing literature and partially validating this finding.

Location of the cyst

In a review of 133 reported ACUM cases with detailed location information, the cyst was detected on the left side in 60 cases (45.11%) and on the right side in 66 cases (49.62%), with rare cases presenting centrally. ⁹ The cystic mass can extend toward the round ligament or broad ligament. In exceptionally sporadic occurrences, they have been documented outside the uterus, such as in the mesoappendix, left uterosacral ligament with adhesion to the sigmoid colon, and in the left lower lumbar region near the jejunum and descending colon.^15–17 However, as these lesions were not accessory to the uterus, they cannot be classified as ACUM.

Clinical symptoms

Severe dysmenorrhea and chronic pelvic pain are the most prevalent symptoms of ACUM and often serve as the primary motivators for patients to seek medical attention. These symptoms can manifest before, during, or after menstruation ¹⁸ and are typically localized to the side where the lesion is present. The cyclic bleeding associated with ACUM, along with the resultant accumulation of pressure within the enclosed cystic space, is considered the primary contributing factor to the pain experienced by patients. ¹⁹ However, these symptoms are common and nonspecific among women of childbearing age, which frequently leads to a lack of self-awareness regarding the necessity for medical intervention. Consequently, gynecologists may misdiagnose or underdiagnose the condition, further complicating the patient’s situation and delaying appropriate treatment.

In the population of older reproductive-age women, ACUM was frequently subject to diagnostic delays and misdiagnosis, although it is not a common disorder. These patients do not present with typical symptoms of ACUM, such as dysmenorrhea or chronic pelvic pain, potentially due to the following factors: (a) alterations in neurosensory thresholds resulting from pregnancy and childbirth in multiparous women or (b) natural intracavity decompression in nulliparous women. However, current limitations—including the low global incidence of confirmed cases, their dispersed geographical distribution, and incomplete collection of pain perception-related medical histories—prevent the identification of supporting evidence for these hypotheses in the existing literature. Our patient had an extremely large cyst and never manifested the abovementioned typical symptoms, which support our hypothesis stated in (a). Future research could include the documentation of factors such as increased pain tolerance in women of advanced reproductive age, thereby contributing to a more comprehensive understanding of ACUM.

A summary of the abovementioned information is shown in Table 1.

Table 1.

Comparison of classical and atypical cases in terms of presentations.

	Classical case	Atypical case
Patients’ age	Childbearing age range	Premenarcheal or postmenopausal
Lesion characteristics	<4 cm	≥4 cm
Clinical symptoms	Severe dysmenorrhea and chronic pelvic pain	Light or no specific symptoms

Auxiliary examinations

Imaging plays a crucial role in the early and accurate diagnosis of ACUM. Transvaginal ultrasonography has emerged as the first-line modality due to its convenience, accuracy, noninvasive nature, and cost-effectiveness. Key ultrasound characteristics of ACUM include the following:^14,20,21 (a) a cystic mass resembling endometriomas situated in the uterine myometrium and separated from the ovary; (b) enclosed fluid within the mass exhibiting ground-glass echogenicity, surrounded by the myometrial mantle; (c) blood flow signals detected at the periphery but not within the lumen; (d) typical localization in the myometrium of the lateral uterine wall, particularly at the attachment site of the round ligament; and (e) a normally developed uterus and both adnexa. Although conventional two-dimensional ultrasound may be limited in identifying specific types of Müllerian duct anomalies, ²² it effectively delineates the size, location, and vascularity of the lesion while also providing a comprehensive view of the pelvic anatomy to exclude other sources of pelvic pain with clear causes, such as adenomyosis, endometriosis, and various genital tract malformations. Three-dimensional ultrasound further enhances visualization of uterine-like structures in the accessory cavity and confirms the normal morphology of the uterine cavity and bilateral fallopian tubes.^20,21

Magnetic resonance imaging (MRI) can complement ultrasound findings in diagnosing ACUM. MRI offers precise localization, morphological characterization of the lesion, and assessment of the mass concerning the entire pelvis, thereby informing surgical approaches and strategies. A hyperintense signal on T1- and T2-weighted sequences indicates hemorrhagic content, while hypointensity of the surrounding tissue on T2-weighted imaging reflects the presence of fibrous tissue. Additionally, a liquid–liquid level within the cyst suggests hemorrhagic content of varying ages. The cyst wall is typically lined with endometrial tissue, which can exhibit slightly hyperintense signals on T2-weighted imaging. ²³ In the presented case, the accessory uterine cavity was initially misdiagnosed as a right adnexal cyst due to ultrasound findings indicating cystic echoes in that region. The exploratory laparoscopy was undertaken based on a straightforward evaluation without the benefit of MRI, which ultimately revealed the ultrasound misdiagnosis during surgery.

Therefore, to reduce the likelihood of misdiagnosis and diagnostic delays, imaging and laparoscopic consideration are routinely recommended for women presenting with unexplained adnexal masses, regardless of age or symptom severity.

Diagnostic criteria

The current diagnostic criteria for ACUM are widely accepted and include the following: ²⁴

1. Presence of an isolated accessory cavitated mass, typically situated beneath the round ligament.

2. Normally developed uterus (including the uterine cavity) with regular anatomical structure of the fallopian tubes and ovaries.

3. The presence of menstrual fluid within the cavity.

4. Lining of the inner cavity with endometrial epithelium, including the presence of glands and mesenchymal stroma, as confirmed via postoperative pathology.

5. Absence of adenomyosis in the uterine body in cases where a hysterectomy has been performed, although small foci adjacent to the mass should still be considered.

6. Confirmation through intraoperative and general postoperative pathological examinations consistent with ACUM.

Although the majority of cases conform to these criteria, some exceptions have been documented. Notably, there have been instances where two ACUMs were found in a single patient, a case where ACUM coexisted with another Müllerian anomaly, and another involving an accessory rudimentary tube attached to the mass. ³ As they do not meet the accepted diagnostic criteria of ACUMs, it is more likely that they represent misdiagnoses.

ACUMs are frequently misdiagnosed as cystic adenomyosis, a subtype of focal adenomyosis arising from the invasion of the endometrial basal layer into the myometrium. ²⁵ Adenomyosis predominantly affects older reproductive-age women (median age: 38–42 years), presenting with severe dysmenorrhea and a history of pregnancy or uterine procedures. ²⁶ MRI further distinguishes adenomyosis through T1-hyperintense/T2-hypointense cystic components surrounded by adenomyotic tissue. ²⁷ Emerging evidence highlights the diagnostic value of immunohistochemistry for differentiating ACUM from adenomyotic cysts.

In the case discussed, the patient did not report significant dysmenorrhea or prior pelvic pain but presented with a palpable lower abdominal mass. Initial ultrasound suggested that the mass originated from the right adnexal region. However, the lack of MRI results required to further assess the mass’s location and characteristics led to a laparoscopic discovery of the mass on the right side of the uterus, exemplifying a case of ultrasound misdiagnosis.

The discussion above reveals that even women of advanced reproductive age or perimenopausal women may have undiagnosed ACUM due to unknown factors such as elevated pain thresholds. Therefore, age alone cannot exclude the possibility of ACUM in patients with pelvic cysts, as demonstrated in this case. We speculate that the ultrasound misdiagnosis in our case may stem from the following two factors: (a) the cyst’s large size obscured precise anatomical localization and (b) the sonographers likely underestimated ACUM probability based on the patient’s perimenopausal age—an assumption-driven bias. As previously proposed, implementing routine imaging evaluations across all age groups would substantially enhance detection rates, especially among older women, enabling timely intervention.

Treatment

Reported treatment options for ACUM include surgical intervention, sclerotherapy, and pharmacological management. As indicated in the literature, nonsteroidal anti-inflammatory drugs, oral contraceptives, gonadotropin-releasing hormone agonists, and levonorgestrel intrauterine devices are frequently employed in the treatment of ACUM. However, the efficacy of these medications in alleviating symptoms is often limited, and symptoms may recur following cessation of treatment.^11,14

Currently, laparoscopic excision is recognized as the most common and effective treatment for ACUM. In cases of smaller ACUM, the challenge of precise localization can complicate surgical procedures, making it crucial to accurately assess the relationship of the ACUM with the myometrium during preoperative evaluations. ²⁸ Some researchers have proposed that utilizing the International Federation of Gynecology and Obstetrics (FIGO) classification for uterine leiomyomas to characterize the location of ACUM within the myometrium may allow surgeons to more accurately predict the depth of myometrial penetration needed for complete lesion excision. ²³ Alternative surgical techniques, including ultrasound-guided radiofrequency ablation, drainage, and robotic-assisted surgery, have also been documented. For patients without fertility considerations, hysterectomy remains a viable option.^14,29

Ethanol sclerotherapy has been employed in several cases, with the earliest documented cases published by Naftalin et al. ¹² and the method first elaborated in the work of Merviel et al. ³⁰ in 2020. This procedure involves draining intracapsular fluid from the ACUM lumen, followed by the injection of an equal volume of 96% ethanol, which is retained for 15 min before being drained. The intention is to destroy the normal endometrial lining within the ACUM, thereby reducing menstrual fluid accumulation within the cyst. The patient experienced immediate symptom relief after the procedure and reported no recurrence of symptoms during a 2-year follow-up. Timmerman et al. ¹⁴ summarized seven cases of ethanol sclerotherapy; of these, three indicated persistent symptoms, and two required laparoscopic lesion excision following the diagnosis of ACUM. Nonetheless, the limited use of this method, small sample sizes, and unclear details regarding treatment protocols (such as ethanol concentration, dosage, and retention duration) highlight the need for further studies and refinement of techniques. In our case, the patient inadvertently received the most effective treatment—laparoscopic surgery—which resulted in a favorable prognosis.

It is noteworthy that ACUM has been categorized under “complex anomalies” in the 2021 edition of the American Society for Reproductive Medicine (ASRM) classification of Müllerian duct anomalies. ³¹ There is an urgent need to standardize terminology in this field to prevent overlapping classifications, which can enhance the understanding and awareness of this condition among gynecologists. Increased recognition will facilitate early diagnosis and treatment of this overlooked anomaly, ultimately promoting women’s health and well-being.

Conclusion

ACUM is a rare Müllerian duct anomaly characterized by dysmenorrhea and pelvic pain as its primary symptoms. The pathogenesis of ACUM remains unclear, emphasizing the necessity for further research. Ultrasound and MRI play pivotal roles as auxiliary examinations, with the key diagnostic criteria including the absence of adenomyosis and the presence of a well-developed uterus and structurally normal adnexa. Surgical resection is recognized as the most common and effective treatment, offering good prognoses for affected patients. Additionally, postoperative pathology can further substantiate the diagnosis of ACUM.

Consent to participate

Written informed consent was obtained from the patient for the use of her personal clinical data for scientific research.

Consent for publication

Written informed consent for the publication of individual medical details and accompanying images was obtained from the participant.

Data availability

All data generated or analyzed during this study are included in this published article and its supplementary information files. Further inquiries can be directed to the corresponding author on reasonable request.

Ethical considerations

All patient information was collected and handled in compliance with ethical standards and was approved by the Ethics Committee of Affiliated Hospital of Shandong Second Medical University.

ORCID iD

Yuan Zhang https://orcid.org/0009-0008-9123-8853