Unicornuate uterus with a non-communicating rudimentary horn discovered during cesarean delivery: a case report

A 31-year-old primigravida at 32 weeks of gestation presented to our academic tertiary hospital with uterine contractions and preterm labor. She reported no underlying medical conditions or prior surgeries. There was no history of infertility, as she conceived spontaneously three months after marriage. Antenatal care included a course of corticosteroids for fetal lung maturation. On admission, her vital signs were stable, and physical examination was unremarkable. Per-vaginal examination revealed cervical dilation of approximately 3 cm. Routine obstetric ultrasonography demonstrated a fetus in breech presentation without additional abnormalities. Laboratory investigations were within normal limits. After obtaining informed consent, the patient was prepared for an emergent lower-segment cesarean section under regional anesthesia. A Pfannenstiel skin incision and a transverse lower-segment uterine incision were performed. A healthy male infant weighing 1800 g was delivered with Apgar scores of 7 and 9. The placenta was removed, and the uterus was closed in two layers. Estimated blood loss was within the expected range for routine cesarean delivery, and no intraoperative complications occurred. Incidentally, following uterine contraction and inspection of the adnexal structures, a left non-communicating rudimentary horn was identified, and the uterus appeared unicornuate (Fig. 1 ). Both ovaries and fallopian tubes were normal. Based on these findings, a diagnosis of unicornuate uterus with a non-communicating rudimentary horn, subtype A1b, was established. Figure 1. An intraoperative photograph demonstrates the unicornuate uterus (black arrow). The non-communicating left rudimentary horn is indicated by the red arrow, while the right and left adnexa are shown by the white arrows. An intraoperative photograph demonstrates the unicornuate uterus (black arrow). The non-communicating left rudimentary horn is indicated by the red arrow, while the right and left adnexa are shown by the white arrows. A postoperative ultrasonographic evaluation, performed 24 h later, confirmed the contracted unicornuate uterus with a decidual reaction in the endometrium and the left non-communicating rudimentary horn (Fig. 2 ). Evaluation of the urinary system revealed no anomalies other than mild bilateral hydronephrosis. Figure 2. Postoperative gynecologic ultrasound demonstrating the unicornuate uterus (black arrows) and the non-communicating left rudimentary horn (red arrows). Image A shows the sagittal view, and Image B shows the coronal view. Postoperative gynecologic ultrasound demonstrating the unicornuate uterus (black arrows) and the non-communicating left rudimentary horn (red arrows). Image A shows the sagittal view, and Image B shows the coronal view. The postoperative course was uneventful, and the patient was discharged in good condition 48 h after surgery. She was advised that future pregnancies should be monitored closely, given the increased risk of obstetric complications associated with a unicornuate uterus and its related reproductive challenges.

Congenital anomalies of the uterus, resulting from abnormal development of the Müllerian ducts during fetal life, are important contributors to gynecologic and obstetric morbidity. Collectively, these anomalies are termed Müllerian duct anomalies (MDAs) [ 1 ] . During embryogenesis, the bilateral Müllerian ducts normally extend caudally and medially to fuse, forming the uterus, cervix, and upper vagina. Failure of complete development of one Müllerian duct, combined with incomplete fusion with the contralateral duct, leads to the formation of a unicornuate uterus. This anomaly accounts for approximately 10% of all MDAs [ 2 , 3 ] . The estimated prevalence in the general population is 0.1% [ 4 ] . HIGHLIGHTS Unicornuate uterus with a non-communicating rudimentary horn is a rare Müllerian duct anomaly, often diagnosed incidentally during pregnancy or surgery. Preterm labor and breech presentation in this case reflect the known obstetric risks associated with a unicornuate uterus. Routine antenatal ultrasonography may fail to detect non-communicating rudimentary horns, underscoring diagnostic limitations. Intraoperative inspection during cesarean delivery provides a critical opportunity to identify previously unrecognized uterine anomalies. Early recognition of Müllerian anomalies enables appropriate counseling and optimized management in future pregnancies. HIGHLIGHTS Unicornuate uterus with a non-communicating rudimentary horn is a rare Müllerian duct anomaly, often diagnosed incidentally during pregnancy or surgery. Preterm labor and breech presentation in this case reflect the known obstetric risks associated with a unicornuate uterus. Routine antenatal ultrasonography may fail to detect non-communicating rudimentary horns, underscoring diagnostic limitations. Intraoperative inspection during cesarean delivery provides a critical opportunity to identify previously unrecognized uterine anomalies. Early recognition of Müllerian anomalies enables appropriate counseling and optimized management in future pregnancies. Clinical manifestations of a unicornuate uterus with a rudimentary horn vary considerably, ranging from asymptomatic presentations to menstrual dysfunction, dysmenorrhea, torsion of the rudimentary horn, and significant obstetric complications. Reported reproductive outcomes include infertility, recurrent first- and second-trimester miscarriages, preterm birth, fetal growth restriction, and malpresentation [ 5 ] . Pregnancy may also occur within the rudimentary horn, a rare but serious event associated with a high risk of uterine rupture and an estimated maternal mortality rate of 0.5% [ 6 ] . Accurate diagnosis relies on imaging modalities such as ultrasonography, hysterosalpingography, hysteroscopy, laparoscopy, and magnetic resonance imaging (MRI), which are critical for delineating uterine anatomy and guiding management [ 7 ] . Here, we present the case of a woman with a previously undiagnosed unicornuate uterus and a non-communicating rudimentary horn, who conceived spontaneously, experienced preterm labor at 32 weeks of gestation, and delivered a healthy infant via cesarean section. This case report has been prepared in accordance with the SCARE criteria [ 8 ] .

Congenital uterine abnormalities, collectively referred to as MDAs, result from abnormal formation, fusion, or resorption of the Müllerian (paramesonephric) ducts during fetal development. Their prevalence is estimated to be 3–5% in the general population, although true rates vary due to differences in clinical presentation and diagnostic methods [ 9 ] . MDAs have a polygenic and multifactorial etiology involving complex genetic and environmental interactions, and most affected individuals have a normal 46,XX karyotype [ 10 ] . Failure of one Müllerian duct to fully develop and elongate results in a unicornuate uterus, one of the MDAs most strongly associated with infertility. In this condition, the ipsilateral Müllerian structures may undergo complete agenesis, although, more commonly, a rudimentary uterine horn is present [ 1 , 11 ] . According to the 2021 American Society for Reproductive Medicine classification – an updated version of the earlier American Fertility Society system – unicornuate uterus is subdivided into four variants [ 12 ] (Fig. 3 ): Rudimentary horn with functional endometrium (A1) Communicating subtype (A1a ): The endometrial cavity of the rudimentary horn communicates with the main uterine cavity. Non-communicating subtype (A1b ): No communication exists between the rudimentary horn and the unicornuate uterus. Atrophic uterine remnant or non-cavity horn (A2 ): a small, non-functional remnant that may be attached to or separate from the unicornuate uterus. No-horn subtype (B ): complete absence of the ipsilateral rudimentary horn and Fallopian tube. Figure 3. American Society for Reproductive Medicine 2021 classification system for Müllerian anomalies. The diagram illustrates the updated categories and subtypes. Rudimentary horn with functional endometrium (A1) Communicating subtype (A1a ): The endometrial cavity of the rudimentary horn communicates with the main uterine cavity. Non-communicating subtype (A1b ): No communication exists between the rudimentary horn and the unicornuate uterus. Communicating subtype (A1a ): The endometrial cavity of the rudimentary horn communicates with the main uterine cavity. Non-communicating subtype (A1b ): No communication exists between the rudimentary horn and the unicornuate uterus. Atrophic uterine remnant or non-cavity horn (A2 ): a small, non-functional remnant that may be attached to or separate from the unicornuate uterus. No-horn subtype (B ): complete absence of the ipsilateral rudimentary horn and Fallopian tube. American Society for Reproductive Medicine 2021 classification system for Müllerian anomalies. The diagram illustrates the updated categories and subtypes. Rudimentary horns are identified in approximately 74% of unicornuate uteri, and among these, 70–90% are non-communicating horns (A1b), as observed in our patient [ 11 , 12 ] . The clinical course of a unicornuate uterus is asymptomatic in many patients, which contributes to its frequent incidental diagnosis. When symptomatic, the anomaly is often identified during evaluation for infertility, endometriosis, hematometra, dysmenorrhea, torsion of a rudimentary horn, or obstetric complications such as ectopic pregnancy, spontaneous abortion, preterm delivery, malpresentation, and fetal growth restriction. For this reason, pregnancies in women with a unicornuate uterus are considered high risk [ 13 , 14 ] . Pregnancy within a rudimentary horn is extremely rare, with an estimated incidence of 1 in 76 000 to 1 in 160 000 pregnancies. It carries a high risk of uterine rupture – often before 20 weeks – and a maternal mortality rate of about 0.5%, regardless of horn subtype [ 15 , 16 ] . Although our patient did not have a rudimentary horn pregnancy, the presence of a non-communicating horn highlights the potential for such life-threatening complications. The patient conceived spontaneously, had no history of infertility or miscarriage, and presented with preterm labor at 32 weeks. Cesarean delivery was performed for breech presentation in accordance with American College of Obstetricians and Gynecologists recommendations to reduce neonatal morbidity and mortality [ 17 ] . The unicornuate uterus with a non-communicating rudimentary horn was discovered incidentally during intraoperative inspection. Antenatal two-dimensional ultrasonography did not identify the anomaly, highlighting the limitations of routine imaging in detecting Müllerian anomalies, particularly non-communicating horns. Although MRI provides superior diagnostic accuracy, it is not routinely performed during pregnancy without clinical suspicion; therefore, only standard antenatal ultrasound was indicated, which explains the missed prenatal diagnosis. Because the genital and urinary tracts share embryologic origins, renal and ureteral anomalies occur in approximately 30–50% of patients with MDAs. Reported abnormalities include unilateral renal agenesis, renal hypoplasia, horseshoe or pelvic kidney, and ureteral duplication. Spinal malformations, such as wedge or rudimentary vertebrae, are described in 10–12% of cases [ 5 , 18 ] . In our patient, no major urinary tract anomaly was identified, aside from mild bilateral hydronephrosis with preserved corticomedullary differentiation. Early diagnosis of MDAs is often missed because clinical manifestations may be subtle or absent, and clinician awareness is limited. Several imaging modalities can assist in evaluation. Transvaginal ultrasonography is commonly used in initial or emergency settings, and three-dimensional ultrasound improves diagnostic accuracy [ 19 ] . However, ultrasound has low sensitivity for detecting a rudimentary horn pregnancy – reported at 29–33% – and sensitivity decreases with advancing maternal age [ 20 ] . MRI remains the gold standard for diagnosing MDAs because it provides detailed visualization of both the uterine cavity and external contours, although its use may be limited by cost and availability. Even so, MRI can occasionally miss a unicornuate uterus or rudimentary horn due to variable pelvic positioning. When diagnostic uncertainty persists, additional modalities such as hysterosalpingography, hysteroscopy, or laparoscopy may offer complementary information [ 21 , 22 ] . Surgical excision of a rudimentary horn, performed via laparotomy or laparoscopy, remains debated. Although removal may prevent complications such as torsion or potential neoplastic transformation, it carries risks, including uterine injury and postoperative adhesions, which may affect future fertility and pregnancy outcomes. For these reasons, excision is generally recommended in cases of rudimentary horn pregnancy, where the risk of uterine rupture necessitates prompt surgical management [ 19 , 23 ] . In our case, surgical removal of the rudimentary horn was not performed because the patient had no symptoms such as cyclic pain or infertility, and the horn was discovered incidentally during a cesarean delivery. Although endometrium was present, there were no clinical indications for immediate excision, so conservative management was appropriate. In the present case, the patient recovered well and was discharged in good condition. She was advised to undergo close antenatal monitoring in future pregnancies to reduce the risk of complications associated with a unicornuate uterus and its associated reproductive challenges.

MDAs, including unicornuate uterus, may still allow normal obstetric outcomes despite their association with significant reproductive risks such as malpresentation and preterm birth, both of which were observed in this case. This report highlights the importance of meticulous intraoperative assessment during cesarean delivery, as congenital uterine anomalies may remain undiagnosed until incidentally encountered. Consistent vigilance in evaluating the adnexa supports timely identification of such anomalies, enables appropriate counseling, and informs optimal management in future obstetric and gynecologic care.