A case of müllerianchoristoma in rectovaginal septum：Developmental Endocervicosis and Developmental Endometriosis –MüllerianosisYaqi Fang1#,Jun Li2#,Fang Zhang1,Yunqian Chen1,Zhongfeng Liu1*1Department of Ultrasound, Yantai Affiliated Hospital of Binzhou Medical University, Yantai, Shandong 264100, China.2Department of Radiology, Yantai Affiliated Hospital of Binzhou Medical University, Yantai, Shandong 264100, China.#These authors contributed equally to this study.*Corresponding author: Zhongfeng Liu, No. 717, Jinbu Street, Department of Ultrasound, Yantai Affiliated Hospital of Binzhou Medical University, Yantai, Shandong 264100, China. Email: [email protected] reportThe presence of Müllerian choristoma in the rectovaginal septum, which containing developmental endocervicosis and developmental endometriosis (müllerianosis), has not been documented in any literature.In this case, we present a patient with heterotopic endocervical tissue and endometrium in the rectovaginal septum. Ultrasound and MRI revealed a lesion within the rectovaginal septum. The final microscopic diagnosis and immunohistochemistry confirmed müllerianosis: developmental endocervicosis and developmental endometriosis. We conclude that our patient has a benign müllerianchoristoma (müllerianosis) with a lesion similar to those previously described by Marwan Habiba[1] and Ronald E.Batt et al[2], except for its location. To our knowledge,this is the first documented case of müllerianchoristoma inrectovaginal septum.Müllerianosis may be defined as an organoid structure of embryonic origin that incorporated within other normal organs during organogenesis[3]. A 36-year-old patient, gravida 1 para 1, has been experiencing bloody stool and constipation for the past two years.A transvaginal scan was performed using a head scanning probe. The ultrasound examination revealed an echo reflection in the intrauterine cavity that resembled an endometrial polyp, as well as endometriosis-like echoes in the right ovary. Furthermore, the scan detected a pelvic effusion and an uneven high echo clump in the rectovaginal septum.The transvaginal biplane ultrasound transducer was used to scan the lesions in the rectovaginal septum. A hyperechoic structure resembling ’Pleurotus eryngii’ was detected in the rectovaginal septum (Fig.1). This structure measured approximately 4.98cm in length and consisted of a ’pileus’ and a ’stipe’. The ’pileus’ was positioned leaning forward and in close proximity to the middle part of the posterior vaginal wall (about 0.27cm away from the posterior vaginal wall), while its hollow ’stipe’ tilted backward and downward, opening between the anocutaneous line and the rear of the perineum. The ’pileus’ is surrounded by a hyperechoic cyst wall, which is about 0.1cm thick. The interior of the ’pileus’ contains multiple polyp-like structures with slightly hyperechoic reflections.The area between the ’pileus’ and the hyperecho cyst wall is filled with an anechoic zone with poor sound transmission. Multiple thin-walled anechoic areas with distinct boundariesare scattered in the ’pileus’.The polypoid echo and the muscle fascicle-like ’stipe’ echo extend towards the front of the external opening of the anal canal. CDFI reveals that both the polypoid echo and the ’stipe’ echo exhibit rich blood flow signals(Fig.2). One of these vessels is connectedto thevessels surrounding the anal canal.After injecting sterile ultrasound gel, an increase in the presence of small bubble anechoic areas can be observed between the ’pileus’ and the polyp-like echo.A double-lumen urethral catheter was inserted through the end opening of the ’stipe’,while simultaneously inserting a catheter into the anal canal. The opening of the lesion was found to be approximately 0.2cm away from the front of the external opening of the anal canal (Fig.3).MRI revealedabnormal signals in the rectum,consistent with pelvic endometriosis. Electronic colonoscopy detected a 2cm submucosal bulge in the rectum, located approximately 4cm away from the anus.The bulge was palpable and could be moved upon touch. After administering general anesthesia, it was observed that the polypoid mass had prolapsed between the rear of the perineal body and the anal skin line. The lesion was able to recover to its original position.During laparoscopic exploration of the pelvic cavity, multiple scattered endometriosis lesions were observed within the pelvic cavity.A sinus was detected between the rectum and vagina during the digital rectal examination. The sinus was located 1cm away from the anal verge. Based on these findings, the patient was diagnosed with pelvic endometriosis.Histological sections (Fig.4) of the specimen revealed two types of epithelial components in the examined polypoid tissue: squamous epithelium and glandular epithelium, consistent with the characteristics of Mullerian epithelium. Immunohistochemical examinations found that the epithelial cells exhibited diffuse expression of PAX-8, and both their histomorphology and immunomarkers were consistent with those of cervical glandular epithelium. Immunohistochemistry analysis also revealed SMA expression. The glandular cells in the cyst wall exhibited a higher proportion of cell nucleus, which were pen-shaped and located at the bottom of the cells, resembling Mullerian epithelium.The positive expression of CD10 in immunohistochemistry supported that these glands and the interstitium shared similar characteristics with the endometrium.The histological analysis and immunohistochemical examinations revealed the presence of ectopic endocervixand endometrium within the soft tissues.Based on this,we concluded that this case was müllerianosiscontaining developmental endocervicosis and developmental endometriosis.DISCUSSIONEndometriosis is a prevalent benign illness defined by the presence of endometrial glands and stroma outside of the uterine cavity, primarilyon the ovary, pelvic peritoneum, and rectovaginal septum[4].This case strongly supports the theory ofFour DevelopmentalMüllerian Diseases proposed by Ronald E. Batt et al[2].According to this theory, developmental adenomyosis, endometriosis, endosalpingiosis, and endocervicosis are referred to as the 4 developmentalmüllerian diseases[2]. In this case, the lesion was found in the rectovaginal septum, with no direct communications with the endocervix, endometrium, or endosalpinx.Immunohistochemistry analysis also revealed SMAexpression. Bundles of differentiated smooth muscle tissue were observed surrounding the cervical stromal cells and cyst wall-like structures,suggesting that epithelial cells induce the simultaneous development of surrounding smooth muscle during the formation of ectopic tissue. Additionally, epithelial cells contribute to the development of smooth muscle tissue during embryonic development.These findings support that this is a developmental (embryonic origin) müllerian disease rather than an acquired müllerian disease.Our hypothesis is that the hyperechoic cyst wall surrounding the ’pileus’ is comparable to the concept of ’peritoneal pocket’described by Batt R E in 1990[5] and 2007[3] . The term ’peritoneal pocket’ was proposed to represent an organoid structure, where the floor of this structure could be grasped and turned inside out for excision. In this case, a similar eversion state was observed.The cells in the cyst wall surrounding the ’pileus’ exhibit characteristics of Mullerian epithelium. The presence of bloody stool and constipation can be attributed to the developmental endometriosis of the cyst wall. This condition is influenced by hormones and undergoes periodic shedding and bleeding. The blood passes through the tube that opens between the anocutaneous line and the perineal body, leading to the presence of bloody stool. Additionally, constipation can be caused by straining to defecate and the presence of everted multiple polyps that block the external anal opening.In this case, müllerianosis lesion is located in the lower-middle part of the rectovaginal septum at the end of the midline of the human body, which is consistent with the distribution of lesions described by Batt RE[2, 6],Hattori H[7], Andronik IshkhanKalayjyan[8], Pansera[9],Buerger[10],Xueyan Chen[11],and others.Based on Ludwig’s theory[12], Batt R.E predicted that no cases of endocervicoticchoristomas will be found above the diaphragm[6]. Conversely, it is predicted that no cases of endosalpingiosischoristomas will be found below the pelvic diaphragm.Whether this prediction can be established requires the discovery of new cases for verification.