Accessory cavitated uterine malformation: A rare mullerian anomaly-case report

Background: Accessory Cavitated Uterine Malformation (ACUM) is a rare Müllerian anomaly characterised by a non -communicating, endometrium -lined cavity within an otherwise normally formed uterus. Because external uterine morphology and menstrual flow often appear normal, ACUM is frequently misdiagnosed as endometriosis, juvenile cystic adenomyoma, or fibroid degeneration. Patients typically present with severe cyclic pelvic pain from adolescence, and symptoms often persist despite conventional medical therapy. Case Report: A 21 -year-old woman presented with progressively worsening dysmenorrhoea, recurrent lower abdominal pain, and irregular menstrual cycles. She had been treated elsewhere for one year as a presumed case of endometriosis, with only partial and temporary relief. On evaluation at our centre, ultrasonography revealed a well -defined hypoechoic lesion (2.3 × 2.6 cm) with a central anechoic cavity (10 × 8 mm) located in the left upper lateral myometrium. MRI findings supported a diagnosis of a cavitated myometrial lesion compatible with ACUM. In view of persistent symptoms despite prolonged medical therapy, surgical excision was performed. Gross pathology showed multiple soft -tissue fragments containing an intramyometrial cavity. Microscopy demonstrated an endometrial -lined cavity with haemosiderin-laden macrophages and a surrounding myometrial wall, confirming ACUM. Clinical presentation, imaging, and histopathology together established the diagnosis.

This case underscores the need to consider ACUM in young women with refractory dysmenorrhoea, abdominal pain, or symptoms unresponsive to endometriosis treatment. Early recognition with appropriate imaging and confirmatory histopathology facilitates timely surgical management, which remains curative and significantly improves quality of life.

Accessory cavitated uterine malformation, dysmenorrhoea, müllerian anomaly, intramyometrial cyst, case report

Accessory Cavitated Uterine Malformation (ACUM) is a rare Müllerian anomaly characterized by a non -communicating, endometrium -lined accessory cavity within an otherwise structurally normal uterus [1]. The lesion is typically located beneath the insertion of the round ligament, surrounded by a myometrial mantle, and separate from the main endometrial cavity [2]. Because of its rarity and non -obvious external uterine distortion, ACUM is frequently misdiagnosed as juvenile cystic adenomyoma, noncommunicating uterine horn, degen erating fibroid, or adenomyosis [2, 3]. Clinically, ACUM often presents in adolescents or young adults with severe, cyclical dysmenorrhoea or chronic pelvic pain, resistant to standard medical management [4, 5] . The accessory cavity contains functional endometrium, which undergoes cyclical menstruation; because there is no outflow, blood accumulates leading to progressive distension, intracystic hemorrhage, and haemosiderin deposition - correlating with the worsening pain over successive cycles [1, 3] . Imaging plays a pivotal role in preoperative diagnosis. Transvaginal or 3D ultrasonography may reveal a well -circumscribed intramyometrial cystic mass, while magnetic resonance im aging (MRI) is more definitive showing a myometrium -surrounded cavity with blood-product signal intensity, a normal uterine contour, and a separate normal endometrial cavity [5, 6]. Despite these imaging tools, diagnosis is often delayed because many clinicians are unaware of ACUM’s distinct entity [2, 7]. International Journal of Clinical Obstetrics and Gynaecology https://www.gynaecologyjournal.com ~ 189 ~ Because of recurrent pain and impact on quality of life, surgical excision (usually via minimally invasive laparoscopy) is considered the treatment of choice, often resulting in complete symptom relief while preserving uterine integrity [1, 4]. Hence, we report this case to emphasize the classical presentation, imaging and histopathological findings of ACUM in a 21 -year-old woman with progres sive, refractory dysmenorrhoea aiming to raise awareness among clinicians to consider ACUM in the differential diagnosis and ensure timely, fertility-sparing management. Case Presentation A 21 -year-old woman presented to us with a long -standing history of progressively worsening dysmenorrhoea. She additionally complained of recurrent lower abdominal pain and irregular menstrual cycles, a combination that had increasingly interfered with her daily routine. She had been treated elsewhere for one year for a provisional diagnosis of endometriosis, during which she received conservative and hormonal therapies but obtained only partial and short-lasting relief. The pain occurred with every menstrual cycle, typically beginning on day one and persisting through the first few days of menstruation. Despite the use of over -the-counter analgesics and antispasmodics, she experienced only minimal and temporary relief. The severity of pain resulted in recurrent hospital admissions, each episode characterised by sharp lower abdominal discomfort severe enough to restrict routine activities. She denied any history of heavy menstrual bleeding, intermenstrual spotting, or passage of clots. She had no known history of genitourinary infections, hormonal treatment prior to the past year, or previous pelvic surgery. No systemic symptoms such as fever, weight loss, or gastrointestinal disturbances were noted. Because her symptoms persisted despite prolonged treatment, she presented to our centre for further evaluation. We performed pelvic ultrasonography (USG) which revealed anteverted uterus of normal size and echotexture , without distortion of the main endometrial cavity. Within the left lateral myometrium of the upper uterine segment, a well -marginated hypoechoic lesion measuring 2.3 × 2.6 cm was identified. The lesion contained a central anechoic area of 10 × 8 mm, suggestive of fluid or haemorrhagic content, surrounded by a uniform hypoechoic rim approximately 8 mm thick, consistent with a myometrial envelope. The endometrial cavity was empty with a thickness of 7 mm, appropriate for the phase of the menstrual cycle. Both ovaries were normal in size and morphology with no adnexal masses or free fluid in the pouch of Douglas. (A) (B) International Journal of Clinical Obstetrics and Gynaecology https://www.gynaecologyjournal.com ~ 190 ~ (C) (D) (E) Fig 1: (A) to (E) Show ultrasound findings International Journal of Clinical Obstetrics and Gynaecology https://www.gynaecologyjournal.com ~ 191 ~ Based on these findings, the radiologist considered the lesion highly suggestive of an accessory cavitated uterine mass and recommended MRI for further evaluation. MRI was subsequently performed. Fig 2: MRI Findings In view of the typical imaging appearance along with her persistent symptoms despite prolonged medical therapy, surgical management was planned. International Journal of Clinical Obstetrics and Gynaecology https://www.gynaecologyjournal.com ~ 192 ~ Fig 3: Intra-operative images She underwent surgical excision of the suspected mass, and the tissue was submitted for histopathological evaluation. On gross examination, the specimen consisted of multiple soft -tissue fragments collectively measuring 4 × 2.5 × 1.5 cm. The cut surface revealed a small cavity -like structure filled with altered material. Microscopic evaluation showed a well -defined cavity lined by thin endometrial epithelium, confirming the presence of functioning endometrial tissue. The stroma contained haemosiderin-laden macrophages, indicative of repeated intracavitary bleeding. Surrounding the cavity were thick bundles of mature myometrial smooth muscle, sharply demarcating the accessory cavity from the main uterine cavity. No atypia, hyperplasia, or malignancy was noted. These features were consistent with an Accessory Cavitated Uterine Malformation (ACUM). Clinical symptoms, imaging findings, and definitive histopathology together confirmed ACUM as the cause of this patient’s refractory and progressively worsening dysmenorrhoea.

In retrospect, the clinical course of this patient closely fits the pattern now recognised as characteristic of Accessory Cavitated Uterine Malformation (ACUM), a Müllerian anomaly that predominantly affects adolescents and young women. What initially appeared to be refractory d ysmenorrhoea and abdominal pain symptoms for which she had already been treated as presumed endometriosis for nearly a year —ultimately reflected the presence of a concealed, functioning accessory uterine cavity. This delay in diagnosis is not surprising, as Timmerman International Journal of Clinical Obstetrics and Gynaecology https://www.gynaecologyjournal.com ~ 193 ~ et al . (2024) [8] describe similar cases where ACUM manifests early in reproductive life with severe cyclic pelvic pain that responds poorly to conventional analgesics. Hu et al. (2024) [9] also reported that many young patients undergo prolonged treatment for dysmenorrhoea or endometriosis before the underlying anomaly is identified. Our experience aligns with these observations, reinforcing the need to consider ACUM in the differential diagnosis of persistent, unexplained pelvic pain in young women. The imaging features in our case were highly illustrative. The well-defined intramyometrial cystic lesion with a central cavity on ultrasound closely resembled descriptions by Gupta et al . (2023) [2], who noted similar lesions located near the round ligament insertion. The MRI characteristics, including the presence of haemorrhagic content within a thick myometrial wall, matched the findings reported by Shen et al . (2025) [11]. Despite this, ACUM is still frequently overlooked. Thakur et al. (2025)¹² noted that many cases are initially misinterpreted as adenomyosis, juvenile cystic adenomyoma, or cystic degeneration of fibroids differentials that were also considered in our patient before deeper evaluation. Zhang et al . (2025) [4] highlighted this diagnostic uncertainty, emphasising that young women with disproportionate pelvic pain warrant targeted imaging to avoid misdiagnosis. Histopathology in our case provided definitive clarity. The presence of endometrial epithelium lining the cavity, haemosiderin-laden macrophages, and a sharply demarcated myometrial envelope was entirely in keeping with the diagnostic criteria proposed by Zhu L et al. (2025) [13]. Similar microscopic findings have been highlighted by Mondal and Bhave (2023) [7] and Ferreira et al . (2025) [14], who emphasised that recurrent intracavitary bleeding is central to symptom generation. The histological picture in our patient strongly supports this mechanism, explaining her progressively worsening cyclical pain despite treatment. Surgical excision proved to be the definitive therapeutic intervention. Our outcome aligns with published evidence: Hu et al. (2024) [9] reported excellent symptom resolution following laparoscopic removal of ACUM lesions, while Vidyasagara et al. (2025) [15] observed complete relief in similar cases. Rackow (2022) [1] has also stressed that early surgical management prevents prolonged morbidity and preserves normal uterine architecture, particularly important for future fertility. From this experience, it is evident that ACUM remains an underdiagnosed yet significant cause of severe dysmenorrhoea and pelvic pain in young women. This case underscores the importance of maintaining clinical suspicion especially when symptoms persist despite standard therapy fo r conditions like endometriosis and highlights the value of combining careful imaging interpretation with histopathological confirmation to reach an accurate diagnosis and offer effective, timely treatment.

Accessory Cavitated Uterine Malformation remains an under - recognised cause of severe pelvic pain in young women, and this case clearly illustrates how easily it can be mistaken for more common conditions such as endometriosis. Our patient had been treated for almost a year without meaningful improvement, and it was only when we correlated her persistent symptoms with focused imaging and later histopathology that the correct diagnosis became evident. Surgical excision proved curative, with complete relief of her long -standing pain. This experience reinforces the importance of keeping ACUM in mind when evaluating young women with refractory dysmenorrhoea or unexplained abdominal pain, as timely diagnosis can prevent prolonged suffering and significantly improve quality of life. Conflict of Interest: None. Funding: None. Ethical Approval: Obtained. Consent: Written consent secured.

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