Case Report PelvicPainandAdnexalMass:BeAwareofAccessoryand CavitatedUterineMass PooyaIranpour , 1 SaraHaseli , 1,2 PedramKeshavarz , 3 AmirrezaDehghanian , 4 andNedaKhalili 5 1 Medical Imaging Research Center, Shiraz University of Medical Sciences, Shiraz, Iran 2 Chronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran 3 Department of Diagnostic & Interventional Radiology of New Hospitals LTD, Tbilisi, Georgia 4 Department of Pathology, Shiraz University of Medical Sciences, Shiraz, Iran 5 School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Correspondence should be addressed to Sara Haseli; sarahaseli@gmail.com Received 24 November 2020; Revised 19 January 2021; Accepted 30 January 2021; Published 11 February 2021 Academic Editor: Michael S. Firstenberg Copyright © 2021 Pooya Iranpour et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Accessory and cavitated uterine mass (ACUM) is a rare form of Mullerian anomaly that usually presents in young females with chronic cyclic pelvic pain and/or dysmenorrhea. is clinical entity is often underdiagnosed as it may be mistaken for other differential diagnoses, such as pedunculated myoma or adnexal lesions. Imaging modalities, including ultrasonography and magnetic resonance imaging (MRI), accompanied with relevant and suspicious clinical findings are important tools in making acorrect diagnosis. To date, surgical excision of the mass remains the mainstay of treatment,which provides significant symptom relief. In this study, we present a female adolescent with chronic pelvic pain since menarche who underwent laparotomy with the presumed diagnosis of a left-sided ovarian mass. Retrospective evaluation of pelvic MR images demonstrated that the lesion was in fact an ACUM, which was further confirmed by histopathological examination. 1.Introduction Accessory and cavitated uterine mass (ACUM) is a rare newly described Mullerian anomaly, which generally pres- ents with chronic recurrent pelvic pain and/or severe dys- menorrhea in women younger than 30 years of age [1]. It is an accessory mass at the insertion of the round ligament that is lined by normal endometrium and has a dark-brown- colored fluid content [2, 3]. ACUMs are difficult to diagnose because of their broad differential diagnosis, which includes rudimentary and cavitated uterine horns such as those found in other uterine malformations (e.g., bicornuate uterus), adenomyosis with cystic or degenerated areas, degenerated leiomyomas, and essential and primary dysmenorrhea [4]. To the best of our knowledge, fewer than 60 cases of ACUM are reported in the literature at the time of writing this paper. In this case report, we describe a 14-year-old girl presenting with severe pelvic pain since her menarche. Pelvic magnetic resonance imaging (MRI) showed an apparent adnexal mass, but final histopathological examination was in favor of ACUM. 2.CasePresentation A 14-year-old girl presented with chronic recurrent pelvic pain since her menarche. Her pain aggravated monthly during her menstruation; however, she had a regular and normal menstrual flow. Her personal history and family history were not significant, and she had no previous sexual history. Different kinds of anti-inflammatory medications had been prescribed for her during the past two years. e patient had also received oral contraceptive pills (OCPs) for two months, but none of the medications had been sig- nificantly effective. On physical examination, she was a Hindawi Case Reports in Medicine Volume 2021, Article ID 6649663, 6 pages https://doi.org/10.1155/2021/6649663