BACKGROUND Accessory cavitated uterine malformations, or mass (ACUM) is a Mullerian anomaly which increasingly recognized as a cause of severe dysmenorrhoea and pelvic pain. OBJECTIVE To know what ACUMs are and recognize their clinical presentation, able to diagnose an ACUM using ultrasound or MRI; and counsel patients with ACUMs on the different management options, including conservative, medical, and surgery. CONCLUSION AND WIDER IMPLICATION ACUMs are less rare than previously believed; hence ACUM diagnosis is essential in clinically suspicious cases via ultrasound and MRI, and intra-operative assessment of uterine morphology and laparoscopic surgical excision is the definitive treatment for ACUM.