A 19-year-old virgo intacta student from Sandakan, Sabah presented with severe pelvic pain and dysmenorrhea since menarche at the age of 13. Symptoms were not alleviated with COC or NSAID and she needed frequent visits the ED for NSAID or opioid injections. Ultrasound findings were not conclusive. Hence MRI was performed which showed a bulky uterus with a well-defined rounded non communicating cavitated mass measuring 3.6x 3.7×4 cm within the left myometrium which is hypointense on T1 and T2.  It has central hyperintense cavity on T1 and T2 which may represent haemorrhagic content or proteinaceous fluid. The main uterine cavity has a normal trigone shape with normal fundus and bilateral cornua visualised. Both tubes and ovaries are normal. Impression given by the radiologist was possible accessory and cavitated uterine mass (ACUM).   

Diagnostic hysteroscopy and laparoscopy was performed which showed a normal endo-cervical canal and normal uterine cavity with both ostia seen. There was no endometrial abnormality. The uterus had a vague globular mass located near the insertion of the left round ligament. Both Fallopian tubes and ovaries appeared normal.  Vasopressin was injected into the myometrium to reduce the bleeding.  A transverse incision was made on the anterior uterine surface over the swelling with the Harmonic Scalpel (Ethicon©).  Approximately 5 ml of a thick, chocolate coloured material spilled out during the dissection. Excision, however, was not technically easy as the limits of the mass was ambiguous. The uterine cavity was spared during dissection. The uterine and broad ligament defects were reconstructed with the coated Vicryl 1 (Ethicin®) and V-Loc™ 1 Barbed sutures. The specimen was placed in an endo-bag and retrieved from the peritoneal cavity through a 10mm trocar. The patient was discharged 2 days after surgery. She did not experience dysmenorrhea in her next cycle when she came for follow-up. A repeat hysteroscopy was performed 8 weeks later which showed the uterine cavity to be normal, no defects with bilateral ostia seen.

Macroscopic examination of the lesion showed a 3 cm irregular greyish white nodular mass with a blood filled cyst of 2 cm diameter. The HPE showed a cystic cavity lines by endometrial glands and stroma which confirmed the diagnosis of ACUM.  There were no adenomyotic foci surrounding the myometrial tissue in the excised specimen.

Conclusion: ACUM is a rare Mullerian anomaly. Early diagnosis and surgical intervention removing the mass can shorten the suffering of the patient.