Accessory Cavitated Uterine Malformation (ACUM): A Case Series

Accessory Cavitated Uterine Malformation (ACUM): A Case Series ABSTRACT Accessory Cavitated Uterine Malformation (ACUM) can be misdiagnosed as other uterine pathologies, such as Müllerian anomalies, adenomyosis, or fibroids. In the present case series, we report on data of eleven cases of ACUM. The mean age at diagnosis was 24.5 years. Nine patients presented with abdominal pain, one patient complained of infertility, and one patient was asymptomatic. One patient had a bilateral lesion. The average maximum lesion size was 26 mm. Ultrasound characteristics of the twelve lesions showed cystic lesions located in the uterine cornual region, containing ground glass or anechoic content. Imaging, particularly gynecological ultrasound, plays a fundamental role in identifying this condition. 1 Introduction Accessory Cavitated Uterine Malformation (ACUM), a non-communicating accessory uterine cavity, diagnosis has increased in recent years (Timmerman et al. 2024). The pathogenesis of ACUM is unknown, but it could be caused by the duplication and persistence of ductal Müllerian tissue in the critical area at the attachment level of the round ligament, possibly related to a gubernaculum dysfunction or abnormal traction (Rackow 2022; Zhu et al. 2025). However, ACUM has not been included in current classifications of Müllerian malformations (Grimbizis et al. 2013; Pfeifer et al. 2021). In fact, Acién's proposal was the first and only one to include ACUM as a gubernaculum anomaly (Acién and Acién 2011). ACUM is characterized by an isolated cavitated lesion located in the anterolateral myometrium, in the proximity of the round ligament. The cavity is lined by endometrial tissue and typically filled with hemorrhagic/menstrual fluid. The cavity is surrounded by a myometrial mantle with concentric orientation of myometrial fibers. They are typically associated with a normal uterine cavity (Zhu et al. 2025). ACUM symptoms usually begin between the ages of 13 and 17 years (Timmerman et al. 2024). This entity may present with typical and atypical symptoms. The most frequently reported symptoms are severe menstrual pain that can be central or ipsilateral to the side of the ACUM, and chronic pelvic pain. Other symptoms include dyspareunia and hypogastric pain (Zhu et al. 2025). Among typical presentations, NSAID-refractory dysmenorrhea is reported in approximately 70% of patients (Timmerman et al. 2024; Zhu et al. 2025). In spite of early symptoms, diagnosis is usually delayed, with a median age of 21.5 years at diagnosis (Timmerman et al. 2024). Severe refractory dysmenorrhea should raise suspicion of ACUM, and its diagnosis is based on gynecological ultrasound and magnetic resonance imaging (Zhu et al. 2025). The most common ultrasound findings include a smooth-walled cystic myometrial lesion with echogenic ground-glass content (Zhu et al. 2025). A formal consensus on ultrasonographic criteria for ACUM is currently lacking. Based on recent publications, a diagnosis of ACUM is generally supported by the following features: (1) An isolated cavitated lesion located in the anterolateral myometrium, close to the round ligament. (2) A cavity lined by endometrial tissue, typically containing hemorrhagic or menstrual fluid. (3) A surrounding myometrial mantle with concentric orientation of myometrial fibers. (4) Association with a normal uterine cavity, with no features suggestive of adenomyosis. (5) The lesion has avascular contents on color Doppler, but the myometrial mantle is vascularized similarly to the rest of the uterine myometrium (Acién and Acién 2021; Gupta et al. 2023; Naftalin et al. 2021; Takeuchi et al. 2010; Timmerman et al. 2024). Treatment of ACUM is predominantly surgical, relieving symptoms in 80% of the cases (Timmerman et al. 2024; Zhu et al. 2025). Medical treatment is reserved for selected cases, such as patients who refuse surgery or have manageable symptoms, and includes combined oral contraceptives, progestins, levonorgestrel-containing intrauterine devices, and GnRH analogues, although recurrence after discontinuation is common (Timmerman et al. 2024; Zhu et al. 2025). Emerging interventional methods, such as image-guided drainage and sclerotherapy, require further validation (Zhu et al. 2025). The prevalence of ACUM is unknown. Its recognition as a distinct entity is recent, and its diagnosis can be overlooked. To date, fewer than 130 cases have been reported in the English-language literature. 2 Case Series Herein we present a retrospective case series of eleven patients diagnosed with ACUM in two institutions (six cases from Hospital Quironsalud, Málaga, Spain, and five cases from Centro CDA Endometriosis, Lima, Peru) between May 2024 and March 2025. All patients provided prior informed consent (IRB approval obtained). None of them had suspected ACUM in prior evaluations. Referral diagnoses were endometriosis, uterine fibroids, abdominal pain, ovarian tumor, uterine Müllerian anomaly and adenomyosis. The mean age at diagnosis was 24.5 years (range: 15–42 years). Five patients were Caucasian, five were Latina and one was of African. Nine patients were nulliparous and two were multiparous. Nine patients presented with abdominal pain (50% reporting severe dysmenorrhea and 33% reporting chronic non-cyclical pelvic pain), one patient complained infertility and one patient was asymptomatic. Four cases corresponded to the right side, six to the left, and one was bilateral. The average maximum lesion size was 26 mm. Ultrasound characteristics of the twelve lesions evaluated showed ten cystic lesions, containing ground glass content located in the uterine cornual region (Figures 1-3). In two patients, the lesions had anechoic content. Of particular interest is the use of 3D ultrasound, since this technique allows much better definition of the spatial relationship of the lesion with the uterine cavity (Figures 4 and 5). This is important for avoiding a misdiagnosis of Müllerian anomalies, such as a bicornuate uterus or unicornuate with rudiment cornu uterus (Zhu et al. 2025). All lesions were confirmed in MRI (Figure 6). Regarding treatment, two patients were prescribed analgesic treatment (NSAIDs), while eight patients received hormonal treatment (oral contraceptive). Four out of these ten women did not show symptoms improvement despite medical treatment, so surgery was decided upon in three of them. These patients underwent laparoscopic enucleation of the lesion with subsequent suturing of the uterine wall (Figure 7), achieving complete resolution of symptoms and confirming the histopathological diagnosis of the lesion. One patient underwent sclerotherapy with alcohol, with symptom relief. The asymptomatic patient remained untreated. 3 Discussion Our data agree with those reported in the literature regarding clinic, diagnosis and management of this entity (Timmerman et al. 2024; Zhu et al. 2025). However, it should be noted that we reported the first bilateral ACUM to date. ACUM might be underdiagnosed and it should be considered in the differential diagnosis of severe dysmenorrhea and pelvic pain in young women. In fact, in our case series, no patient was initially suspected of having ACUM. Imaging, particularly gynecological ultrasound plays a fundamental role in identifying this condition. Saline infusion sonohysterography and x-ray hysterosalpingography could have a role since these techniques could show the lesion as independent of the uterine cavity. However, to the best of our knowledge, there are no reports using these techniques for diagnosing ACUM. While surgery remains the treatment of choice, prospective studies are needed to define the long-term impact on fertility and patient quality of life. Author Contributions Conceptualization: Juan Luis Alcazar. Investigation: Luis Felipe Aravena, Colomba Spatafore, Arelana Balazs, Ignacio Brunel, Roberto Albinagorta. Draft writing: Juan Luis Alcazar. Draft reviewing. Rodrigo Orozco. Acknowledgments The authors have nothing to report. Funding The authors have nothing to report. Disclosure The authors have nothing to report. Ethics Statement IRB approval was obtained. Consent Patients gave informed consent for her data to be used anonymously for publishing this case series. Conflicts of Interest The authors declare no conflicts of interest. Data Availability Statement The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.