Diagnostic challenge: functional non-communicating rudimentary horn with ovarian endometriosis and ipsilateral renal agenesis

A 13-year-old nulliparous adolescent presented to our emergency department with a sudden onset of severe lower abdominal pain that had persisted for two days following physical exertion. The pain was accompanied by one day of nausea, vomiting, and febrile episodes. Notably, the patient reported no vaginal bleeding or discharge. On physical examination, she was febrile (38 °C). Abdominal examination revealed tenderness and guarding predominantly in the right lower quadrant, with no palpable mass. Rectal examination identified a 12 cm pelvic mass on the right side, which exhibited ill-defined borders, restricted mobility, and marked tenderness. The patient’s gynecological history was significant: menarche had occurred at age 10, with regular 30-day menstrual cycles of normal duration and flow. She reported that initial dysmenorrhea had progressively intensified during the first two post-menarchal years, but unexpectedly resolved one year prior to this acute presentation. Her last menstrual period had occurred 20 days before admission. Initial diagnostic evaluation included CT imaging performed at a peripheral hospital, which revealed multiple quasi-circular hypodense pelvic lesions, ascites in both abdominal and pelvic cavities, a non-dilated appendix with visualized fecaliths, and right renal agenesis with compensatory left renal hypertrophy. Subsequent transrectal ultrasonography at our institution demonstrated an 11.3 × 5.3 cm heterogeneous echogenic mass in the right pelvic region, along with an 8.1 × 3.5 cm complex fluid collection in the Douglas pouch containing dense echogenic foci. The uterus measured 3.7 × 3.1 cm with 0.8 cm endometrial thickness, and the left ovary appeared normal at 3.7 × 2.4 cm. The right ovary was poorly visualized. Laboratory investigations revealed leukocytosis (15.02 × 10⁹/L) with neutrophilic predominance (89.10%), alongside normal hematological, hepatic, and renal parameters. Tumor markers showed significant elevation: CA-125 4039 U/mL and CA19-9 558 U/mL. Other tumor markers including HCG, AFP, CEA, and HE4 were negative. The diagnostic approach evolved significantly at this stage. The emergency physician initially considered ovarian cyst torsion or rupture based on the clinical presentation and imaging findings. However, upon review by senior clinicians, attention was drawn to the unilateral renal agenesis observed on CT (Fig.  1 ). Given the established association between renal agenesis and Müllerian anomalies, further evaluation with MRI was pursued to assess for potential reproductive tract malformation. Fig. 1 Computed tomography (CT) images of the abdomen: ( A ) left compensatory renal hypertrophy and absence of the right kidney; ( B ) normal left unicornuate uterus; ( C ) right rudimentary horn of the uterus; ( D ) pelvic cysts Computed tomography (CT) images of the abdomen: ( A ) left compensatory renal hypertrophy and absence of the right kidney; ( B ) normal left unicornuate uterus; ( C ) right rudimentary horn of the uterus; ( D ) pelvic cysts Pelvic MRI revealed a bicornuate uterine configuration with right cervical narrowing forming a linear vaginal connection, raising strong suspicion of obstructive reproductive tract malformation. Multiple thin-walled cystic pelvic lesions demonstrated T1 hyperintensity and T2 mild hyperintensity, consistent with ovarian endometriomas (Fig.  2 ). Fig. 2 A Pelvic MRI coronal schematic views; ( B ) Pelvic MRI coronal plane images; ( C ) Pelvic MRI axial plane image. Red arrows: Right-sided rudimentary uterine horn; White arrows: Normal left unicornuate uterus. Patent communication between the left uterine cavity and vagina is visualized in panels B and D; Yellow boxes: Dilated fallopian tube and associated ovarian cyst A Pelvic MRI coronal schematic views; ( B ) Pelvic MRI coronal plane images; ( C ) Pelvic MRI axial plane image. Red arrows: Right-sided rudimentary uterine horn; White arrows: Normal left unicornuate uterus. Patent communication between the left uterine cavity and vagina is visualized in panels B and D; Yellow boxes: Dilated fallopian tube and associated ovarian cyst The patient underwent exploratory laparotomy, which disclosed hemosiderin deposition on the greater omentum and a 12 × 10 × 8 cm right ovarian endometrioma containing chocolate-colored fluid, extensively adherent to surrounding omental and abdominal wall structures. The ipsilateral fallopian tube appeared thickened and hemorrhagic with intraluminal blood clots. Critically, a 5 × 5 × 4 cm functional right uterine rudimentary horn containing hematometra was identified, connected to the left uterine corpus via a fibromuscular band, lacking discernible cervical or vaginal continuity. Ruptured chocolate-colored fluid was observed in the pelvic and abdominal cavities. The left adnexa remained anatomically intact despite extensive adhesion involving the right ovarian cyst, hematosalpinx, and ipsilateral pelvic structures (Fig.  3 ). Fig. 3 A  Intraoperative anatomical findings; ( B ) Postoperative gross specimen. Yellow arrows: Rudimentary uterine horn with functional endometrium; Green arrows: Dilated fallopian tube; Red arrows: Ovarian endometrioma. A  Intraoperative anatomical findings; ( B ) Postoperative gross specimen. Yellow arrows: Rudimentary uterine horn with functional endometrium; Green arrows: Dilated fallopian tube; Red arrows: Ovarian endometrioma. Surgical intervention included adhesiolysis followed by right ovarian cystectomy, excision of the rudimentary uterine horn with ipsilateral salpingectomy, and partial adherent omentectomy. Histopathological examination confirmed an endometriotic ovarian cyst and functional endometrial tissue within the resected uterine horn. Postoperative recovery was uncomplicated. At two-month follow-up, the patient reported complete resolution of dysmenorrhea and restoration of regular menses. CA-125 and CA19-9 levels normalized during subsequent surveillance (Scheme 1 ). Scheme 1 Clinical Timeline of Diagnosis and Treatment Clinical Timeline of Diagnosis and Treatment

In evaluating women presenting with acute abdominal pain to emergency departments, clinicians must meticulously assess subtle clinical indicators, including potential urinary tract anomalies, while systematically evaluating for concurrent Müllerian malformations. Detailed menstrual history documentation combined with pelvic MRI emerges as an indispensable diagnostic paradigm, providing critical insights into reproductive organ architecture that enables the formulation of tailored surgical strategies while mitigating procedural risks.

Female genital tract malformations primarily stem from abnormalities in the development, fusion, and canalization of the paramesonephric duct, also known as the Müllerian ducts, which originates from invaginations of the coelomic epithelium. The specific manifestation of the malformation is determined by the precise point at which the developmental process was disrupted by internal and external factors [ 4 ]. A rudimentary horn uterus results from a developmental disorder of the paramesonephric duct on one side, with an incidence rate in the general female population ranging from 1 in 4000 to 1 in 1000 [ 5 ]. This particular type accounts for a prevalence of 2.4% to 13.7% of all uterine abnormalities [ 6 ]. In 1979, Buttram VC of the American Society of Reproductive Medicine (ASRM) categorized this malformation into three types based on the characteristics of the rudimentary horn, including communication or lack thereof, presence or absence of a cavity. Subsequently, ASRM introduced an additional type IV (Fig. 4 ) [ 7 , 8 ]. This classification system enhances precise interdisciplinary communication and facilitates appropriate clinical management. The patient under consideration falls into Type II, characterized by functional endometrium in the absence of communication with the unicornuate uterus. The European Society of Human Reproduction and Embryology and the European Society for Gynecologic Endoscopy (ESHRE/ESGE) classification system provides another widely recognized framework for categorizing uterine anomalies. This system further stratifies rudimentary horns into two distinct subtypes based on the presence of functional endometrial tissue within the rudimentary structure [ 9 ]. In the present case, the patient’s anatomical findings align with the U4a classification due to the confirmed presence of functional endometrium within the rudimentary horn. Fig. 4 The American Society of Reproductive Medicine 1988: ( A ) represents a functional residual horn that communicates with the unicornuate uterus; ( B ) depicts a functional residual horn that does not communicate with the unicornuate uterus; ( C ) indicates residual cornua with nonfunctional endometrium; ( D ) shows absence of any residual horn The American Society of Reproductive Medicine 1988: ( A ) represents a functional residual horn that communicates with the unicornuate uterus; ( B ) depicts a functional residual horn that does not communicate with the unicornuate uterus; ( C ) indicates residual cornua with nonfunctional endometrium; ( D ) shows absence of any residual horn The various subtypes demonstrate distinct clinical profiles, potentially presenting with a spectrum of manifestations ranging from asymptomatic status to dysmenorrhea, acute/chronic pelvic pain, and ectopic pregnancies. Differential diagnosis for such presentations should include other pelvic pathologies, such as ovarian cysts, tubo-ovarian abscesses, ectopic pregnancies, and other Müllerian anomalies, which require comprehensive imaging (e.g., MRI) and clinical evaluation to avoid misdiagnosis. Type II rudimentary horn anomalies necessitate emergent surgical intervention due to their characteristic endometrial functionality. This functional endometrium predisposes patients to hematometra formation from menstrual blood retention and elevates the risks of rudimentary horn pregnancies. Definitive management involves complete excision of the anomalous structure, achievable through either minimally invasive laparoscopic techniques or traditional laparotomy [ 10 ].In this case, laparotomy was preferred over laparoscopy due to the initial diagnostic uncertainty, the large size of the lesion, and the challenges associated with specimen retrieval and complete excision via minimally invasive approaches, which could increase the risk of incomplete removal or intraoperative complications. During embryogenesis, the urinary and reproductive systems share a common developmental origin, both arising from the mesodermal urogenital ridge. From the fourth gestational week, the mesonephric duct initiates urinary system formation while concurrently inducing paramesonephric duct development. Bilateral paramesonephric ducts subsequently undergo progressive fusion and differentiation from the sixth week onward, establishing the foundation for female reproductive organogenesis. This shared embryological origin explains the frequent coexistence of Müllerian duct anomalies with renal malformations. Genetic studies have identified potential candidate genes (e.g., HNF1B, WNT4) that may contribute to both renal and Müllerian abnormalities, suggesting shared genetic pathways in their development [ 11 ].Current evidence indicates that approximately 30% of women with paramesonephric duct defects demonstrate ipsilateral urinary tract abnormalities, rising to 40% in those with rudimentary uterine horns. Associated renal anomalies encompass horseshoe kidney, duplex collecting systems, pelvic kidney, ectopic ureteral insertion, and renal agenesis [ 12 , 13 ]. The strong association between unilateral renal agenesis and ipsilateral Müllerian anomalies supports the embryological interdependence of these systems. These pathophysiological correlations necessitate routine urinary system evaluation in suspected Müllerian anomalies to prevent iatrogenic surgical complications. Conversely, identified urinary tract malformations should prompt thorough reproductive tract assessment, as demonstrated in our emergency case [ 14 ]. Initial imaging studies failed to detect genital anomalies, leading to provisional diagnoses of ovarian cyst torsion or rupture. However, recognition of ipsilateral renal agenesis prompted advanced MRI evaluation, ultimately revealing the underlying rudimentary uterine horn with coexisting ovarian endometrioma. Studies have shown that girls with congenital contralateral solitary functioning kidney have a high risk (11–30%) of associated Müllerian duct anomalies. However, screening for asymptomatic Müllerian duct anomalies is not yet routine, often delaying detection until menstrual or fertility issues arise. Therefore, early diagnosis with MRI can prevent complications such as endometriosis, infertility, and miscarriage [ 15 ].Romanski found that even well-defined types of Müllerian duct anomalies may exhibit unusual anatomical variations. This study reports three unusual cases of unilateral Müllerian duct obstruction in adolescent females: Cases I and II are variants of OHVIRA syndrome (obstructed hemivagina with ipsilateral renal anomaly), and Case III is a variant of Robert’s uterus [ 16 ]. Cruciat reported a rare case of Müllerian duct anomaly (MDA) in a 30-year-old female, presenting with a right unicornuate uterus with a left non-communicating functional rudimentary horn (ESHRE/ESGE classification U4a). Following initial incomplete surgery, the patient developed severe secondary dysmenorrhea and abdominal wall endometriosis, with the formation of a spontaneous fistula [ 17 ].Müllerian duct anomalies often lead to gynecological and obstetric complications, such as endometriosis, chronic pelvic pain, and pregnancy complications. In this study, the patient presented with unilateral renal agenesis, progressive dysmenorrhea, MRI suggesting multiple pelvic cysts, and surgical exploration revealed ovarian endometriosis. For such cases, early diagnosis and intervention are beneficial for improving long-term prognosis. In Type II rudimentary horn anomalies, mechanical obstruction of menstrual outflow precipitates retrograde menstruation, resulting in hematometra, hematosalpinx, and endometriosis - defined by ectopic implantation of endometrial glands and stroma [ 18 ]. Current evidence demonstrates a substantially elevated endometriosis prevalence ranging from 21% to 31.8% in this population, with Fedele’s seminal work reporting 55% prevalence among obstructive Müllerian anomalies compared to non-obstructive counterparts, thereby supporting Sampson’s retrograde menstruation hypothesis [ 19 – 21 ]. Contemporary systematic reviews have corroborated this association, demonstrating that nearly half (47%) of patients with obstructive anomalies develop endometriosis, compared to 19% with non-obstructive anomalies [ 22 ].Nevertheless, the persistent occurrence of endometriosis in non-obstructive anomalies and post-surgical cases following obstruction correction continues to fuel scientific debate, prompting exploration of alternative etiopathogenic mechanisms, including coelomic metaplasia (first documented by Meyer in 1924) [ 23 ], Müllerian remnant persistence, and immune dysregulation. Recent meta-analyses confirming a 4.7-fold increased risk of endometriosis in obstructive versus non-obstructive anomalies [ 22 ]. Also, the patient in this case developed a 12 cm ovarian endometrioma within merely three years post-menarche, demonstrating an accelerated growth trajectory. Simultaneously, the strict unilateral predilection manifests exclusively on the rudimentary horn side while the contra-lateral ovary, sparing the same pelvic microenvironment [ 24 ]. Current consensus suggests no single theory fully elucidates endometriosis pathogenesis, underscoring the need for continued investigation. Another noteworthy aspect in our case is the significantly elevated levels of CA-125 and CA19-9. It is well established that these tumor markers may be increased in a range of conditions, including inflammatory processes, benign tumors, and malignant neoplasms. Based on clinical experience, a CA-125 level as high as 4039 U/mL is often associated with widespread metastasis in cases of malignancy. However, in this patient, no evidence of distant metastasis was observed apart from pelvic lesions. Therefore, the condition was interpreted as a benign disease exacerbated by acute inflammatory stimulation. The definitive histopathological examination subsequently confirmed the absence of malignancy. Endometriosis associated with congenital reproductive tract anomalies typically manifests earlier, predominantly affecting adolescents and young women (< 21 years). Recent cohort studies of adolescents with obstructive anomalies report endometriosis prevalence up to 46%, with cervical agenesis carrying the highest risk (100%), followed by non-communicating rudimentary horns (75%) and OHVIRA syndrome (43.5%) [ 25 ].Current diagnostic and therapeutic paradigms for this subgroup remain controversial. The revised American Fertility Society (R-AFS) classification remains the predominant staging system, with Heinonen’s observations suggesting predominantly Stage I endometriosis in obstructive anomalies. Audebert’s findings indicate potential spontaneous regression post-obstruction correction without adjuvant therapy. Our case presented Stage III disease (R-AFS score 12), managed surgically without postoperative medical intervention. Updated clinical guidelines recommend initiating pelvic ultrasound screening during early puberty (following breast development) for girls with congenital renal anomalies, with MRI confirmation for suspected cases to enable early intervention and prevent endometriosis progression [ 15 ]. Another question warranting further investigation is the necessity of adjuvant pharmacotherapy. For adolescent endometriosis management, clinical guidelines recommend adapting adult protocols while considering pubertal developmental status. Combined hormonal contraceptives and progestins should be the initial choice for long-term medical management of endometriosis [ 26 , 27 ]. Current recommendations emphasize individualized therapeutic strategies [ 28 , 29 ]. Gonadotropin-releasing hormone agonists (GnRH-a) represent the most widely employed medical intervention, permissible for patients ≥ 16 years with mandatory add-back therapy to mitigate hypoestrogenic bone loss. This case report has several limitations. First, it is based on a single patient, limiting the generalizability of the findings. Second, the follow-up period was relatively short, and long-term outcomes, such as endometriosis recurrence, fertility issues, and the impact of surgical intervention, require further monitoring. Third, while we have highlighted the association between Müllerian anomalies and endometriosis, the precise pathogenic mechanisms remain incompletely elucidated, particularly for non-obstructive anomalies where the endometriosis risk remains elevated despite absent mechanical obstruction [ 30 ]. Future multi-center studies with larger cohorts and extended follow-up are needed to validate these observations and refine management strategies for similar cases.

Common gynecological emergencies include pedicle torsion of ovarian cyst, ovarian cyst rupture, and acute pelvic inflammatory disease. Rare cases, such as obstructive genital tract malformations, also exist. However, these rare cases are often overlooked by emergency physicians due to their low incidence and lack of awareness, leading to potential misdiagnosis or delayed diagnosis [ 1 ]. The incidence of non-communicating functional rudimentary uterine horn is 1/100,000, and its rarity is compounded when presenting with concomitant ovarian endometriosis and ipsilateral renal agenesis [ 2 ]. To date, fewer than 10 such cases have been reported in global literature, and only 3 documented cases had ovarian endometrioma larger than 10 centimeter(cm) [ 3 ]. Here, for expanding the rare case database and equipping clinicians with a critical diagnostic anchor, we present a case involving a non-communicating functional rudimentary uterine horn complicated by hematometra, hematosalpinx, and ovarian endometriosis, manifesting as dysmenorrhea and acute abdominal pain. The diagnosis was aided by the presence of unilateral renal absence.