Severe dysmenorrhea in young women is usually primary dysmenorrhea, but cases with poor response to medical treatment may be due to endometriosis, adenomyosis, or Müllerian duct anomaly [1]. Juvenile cystic adenomyoma is a rare variant of adenomyosis characterized by the presence of a large hemorrhagic cyst resulting from extensive menstrual bleeding in ectopic endometrial glands [2]. Especially in young women, it can present as a focal cystic mass with severe dysmenorrhea, abdominal cramps, and pelvic pain resistant to medical treatment [3]. Currently, this unique entity has been renamed as accessory cavitated uterine mass (ACUM) [4]. ACUM is suggested to be a new variety of Müllerian anomaly that is usually located at the level of the insertion of the round ligament and is related to dysfunction of the female gubernaculum [4]. Therefore, ACUM closely mimics the unicornuate uterus with obstructed cavitated rudimentary horn, and differential diagnosis might not be easy even with the use of pelvic ultrasonography, hysterosalpingography, and magnetic resonance imaging (MRI) [5]. Confirmation of both ostia using hysteroscopy can be helpful in making an accurate diagnosis. Herein, we report two cases of successful laparoscopic mass excision in young women who complained of severe dysmenorrhea, diagnosed as ACUM, with a brief review of the literature.

The typical feature of juvenile cystic adenomyoma or ACUM is early-onset severe dysmenorrhea, which usually starts soon after menarche and is refractory to medical treatments [6]. ACUM was first described by Acién et al. [4] in 2010 and was described as juvenile cystic adenomyosis [6,7]. The diagnostic criteria for ACUM are as follows: (1) an isolated accessory cavitated mass; (2) a normal uterus (endometrial lumen), fallopian tubes, and ovaries; (3) surgical evidence with an excised mass and pathological findings; (4) an accessory cavity lined with endometrial epithelium with glands and stroma; (5) chocolate-brown colored fluid content; and (6) no adenomyosis (if the uterus has been removed), although there could be small foci of adenomyosis in the myometrium adjacent to the accessory cavity [4].

Severe dysmenorrhea accompanied by a uterine mass usually suggests adenomyosis. Even though adenomyosis is usually a diffuse solid mass and develops in women in their forties, it can present as an adenomyoma, adenomyomatous polyps, and cystic adenomyomas [8]. Small cystic spaces, less than 0.5 cm in diameter, may be associated with adenomyosis. However, large adenomyotic cysts, referred to as cystic adenomyomas, are rare [9]. Juvenile cystic adenomyoma is defined as a solitary myometrial cyst measuring ≥1 cm, which is surrounded by hypertrophic endometrium, independent of the uterine lumen, and is present in women less than 30 years of age, in association with severe dysmenorrhea [10]. It is not common in late teenage. However, the youngest case known was a 13-year-old girl [11], and the case in the present study was 14 years old, only 2 years post menarche. To our knowledge, fewer than 40 cases, worldwide, have been reported in the literature [10,12,13]. We agree that most juvenile cystic adenomyomas might, in fact, be ACUMs because they present with similar clinical and histopathological characteristics [4]. When this lesion is considered a variant of adenomyosis, surgeons have to focus on en bloc resection with sufficient margins to reduce the risk of residual adenomyotic lesions in the surrounding myometrium. However, when it is considered a variant Müllerian anomaly, we can expect symptomatic relief only after the endometrial lesion of the cyst wall is eliminated. In our case, the surrounding myometrium did not contain adenomyotic lesions. The patients had complete symptomatic relief after resection of the endometrial lesion lining the cyst wall. However, the pathophysiology of this lesion still remains unclear and needs further study.

Cystic adenomyomas or ACUMs are mostly located in the lateral wall near the uterine round ligament attachment site. They mimic uterine anomalies such as a unicornuate uterus with a rudimentary horn, bicornuate uterus with a noncommunicating horn, and hematometra in uterine didelphys with a transvaginal septum. Additionally, the degenerated myoma and vesicouterine endometrioma are also considered as differential diagnoses [12]. ACUM is a cystic lesion that is independent of the normal endometrium, whereas hematometra and hematocolpos are present in the obstructing Müllerian anomaly [10]. Even with MRI, it can sometimes be difficult to differentiate it from a cavitated noncommunicating rudimentary uterine horn. In this situation, hysterosalpingography and hysteroscopy can be useful in distinguishing it from a uterine anomaly [5]. In our case, the patients were young and complained of unbearable severe dysmenorrhea that developed and progressively worsened from menarche. Therefore, obstructive Müllerian anomaly was first considered, and the interpretation of preoperative MRI was also a uterine anomaly with a noncommunicating horn. However, hysteroscopy showing a normal uterine cavity and ostia were helpful in making the differential diagnosis.

On pathological examination, ACUM is characterized by ectopic endometrial epithelium, glands, and/or stroma within the myometrium. A well-demarcated region of myometrial hyperplasia borders the endometrial tissue and appears as a thick-walled, well-circumscribed lesion within the uterine muscle [14,15].

Initial empirical treatment, including oral contraceptives and analgesia, can be attempted. However, ACUM is usually resistant to medical treatment, and surgical removal might be unavoidable. Laparoscopic excision has been attempted and has shown good postoperative results, comparable to those of exploratory laparotomy [10]. Other surgical approaches have been proposed, such as radiofrequency ablation under ultrasonography guidance [16], single incision with monopolar cautery [17], or the use of robotic surgery [18].

In the cases presented, ACUM was diagnosed in a 14-year-old adolescent girl and a 25-year-old young woman, both presenting with complaints of unbearable severe dysmenorrhea. Laparoscopic mass excision successfully resolved the dysmenorrhea. Early investigation of severe dysmenorrhea in young women can help with appropriate management and reduce the duration of symptoms.