CASE 18326 Published on 10.10.2023

Be aware of a rare cause of dysmenorrhoea: Accessory cavitating uterine mass (ACUM)


Genital (female) imaging

Case Type

Clinical Cases


Prajwal Dahal 1, Sabina Parajuli 2

1 Department of Radiology and Imaging, Grande International Hospital, Kathmandu, Nepal

2 Department of Pathology, Bir Hospital, Kathmandu, Nepal


14 years, female

Area of Interest Genital / Reproductive system female ; Imaging Technique MR, Ultrasound
Clinical History

A 14-year-old girl presented with cyclical pain and tenderness in the right iliac fossa during menstruation for 5 to 6 days since menarche.

Imaging Findings

Transabdominal ultrasonography (USG) (Figures 1a and 1b) showed a lesion measuring 2.4 x 2.2 cm in the right adnexa. The wall of the lesion had echogenicity and vascularity similar to myometrium. The central part of the lesion had echogenicity similar to the endometrial cavity. No communication of the central cavity of the lesion with the endometrial cavity was seen. A plain MRI pelvis was advised for further evaluation.

The MRI pelvis was done after 1 day (Figures 2a, 2b, 2c and 2d). A cavitating lesion was seen in the right side of the uterus just beneath the insertion of the round ligament. Contents of the lesion demonstrated layering in T2 weighted images. The dependent contents were T2 hypointense and the non-dependent contents were T2 hyperintense. In T1 weighted images, the contents demonstrated high signal. In T1 fat-saturated image, the high signal was not suppressed. The cavity of the lesion demonstrated diffusion restriction similar to the endometrial cavity. The cavity of the lesion did not show communication with the endometrial cavity or vagina. Bilateral ovaries and fallopian tubes were normal. The rest of the uterus was normal.



Accessory and cavitating uterine mass (ACUM) is a rare mullerian anomaly. It was first described by Oliver in 1912 as juvenile cystic adenomyosis and recently grouped as ACUM by Acién et al [1]. ACUM is defined as a non-communicating accessory cavitating mass in the uterus or broad ligament in the vicinity of the insertion of round ligament [2]. ACUM has a cavity lined by functional endometrium and surrounded by normal myometrium. The endometrium is sloughed off in each menstrual cycle. Due to lack of drainage, blood products accumulate in the cavity and pressure builds up resulting in pain and tenderness. The criteria for diagnosing ACUM are [3]:

  • An accessory cavitatory mass located under the round ligament. The cavity should not be communicating with the main endometrial cavity.
  • Normal uterus, fallopian tubes and ovaries.
  • Surgical case with pathologically proven accessory cavity lined by endometrial epithelium with glands and stroma.
  • Central cystic component containing blood products.
  • No adenomyosis in the rest of the uterus, although there could be tiny foci of adenomyosis in the myometrium of the accessory cavity.

Clinical Perspective

The typical patient is a young female with dysmenorrhoea and chronic pelvic pain. Pain begins after menarche in the location of the lesion and increases progressively. Pain is aggravated during menstruation. Sometimes, the patient may present with subfertility or infertility.

Imaging Perspective

In USG, ACUM appears as a cystic adnexal mass. The contents might have variable echogenicity. Occasionally, the endometrial lining of the cavity can be appreciated. The lesion is surrounded by normal myometrium. Hysteresalpingography (HSG) can be done to demonstrate normal fallopian tubes and to rule out another mullerian anomaly. Since our index case was an unmarried female, HSG was not performed. MRI is the investigation of choice for ACUM. On MRI, an accessory cavitatory mass is seen beneath the insertion of round ligament. The cavity contains blood products and does not communicate with the endometrial cavity. The blood products are usually hyperintense in T1-weighted images and show layering or shading in T2-weighted images [1]. The cavity is surrounded by normal myometrium.


Conservative treatment with analgesics is given initially. Surgical resection is required for definite treatment [4]. Fertility is preserved after surgical resection. Hormonal therapy with oral contraceptive pills and gonadotropin-releasing hormone can be used in those who want to avoid surgery. However, hormonal therapy is not the definitive treatment option. Sclerotherapy is the upcoming method of treatment [4].

Take Home Message / Teaching Points

  • ACUM is a rare mullerian anomaly in which there is an endometrium-lined accessory cavitatory mass surrounded by normal myometrium around the insertion of the round ligament. The cavity does not communicate with the endometrium. The cavity contains blood products.
  • The typical patient is a young female with dysmenorrhoea and chronic pelvic pain.
  • The radiologists may misdiagnose ACUM due to lack of familiarity with the condition.
  • Surgical resection is the treatment of choice.
Differential Diagnosis List
Accessory and cavitating uterine mass (ACUM)
Unicornuate uterus with obstructed rudimentary horn
Cystic degeneration of fibroid
Cystic degeneration of adenomyoma
Congenital myometrial cyst
Final Diagnosis
Accessory and cavitating uterine mass (ACUM)
Case information
DOI: 10.35100/eurorad/case.18326
ISSN: 1563-4086