Unruptured ectopic pregnancy in a noncommunicating rudimentary horn of a unicornuate uterus: a rare case report

A 25-year-old nulliparous female, married for 6 months, with no previous obstetrical, gynecological, or surgical history, presented to the emergency department after 9 weeks of amenorrhea with a new-onset acute pelvic pain. On physical examination, the patient was hemodynamically stable with blood pressure 100/70 mmHg, heart rate 96 bpm, and a body temperature of 36.9; her abdomen was soft but with tenderness over the left lower pelvic quadrant. On vaginal examination, the single cervical os was closed, with no vaginal bleeding. On bimanual examination, cervical motion tenderness was present. Urination and defecation were normal. The patient was admitted, and her transvaginal and transabdominal sonography was performed, which showed an empty uterus with decidual reaction in the endometrium. There was a well-defined gestational sac which contained a viable embryo of 8 4/7 weeks according to Crown-Rump Length (CRL) with cardiac activity in the left adnexal region, surrounded by a wall similar with its echogenicity to the myometrium (Figs 1 and 2 ). There was no free fluid in the peritoneal cavity, and no visual communication between the gestational sac and cervical canal was observed, leading to a presumptive diagnosis of pregnancy in a left rudimentary horn. Figure 1. The gestational sac containing the fetus with cardiac activity. Figure 2. The rudimentary horn with the gestational sac inside (red arrow) and the empty uterus (blue arrow). The gestational sac containing the fetus with cardiac activity. The rudimentary horn with the gestational sac inside (red arrow) and the empty uterus (blue arrow). Laboratory tests showed normal leucocytes’ count (WBCs) 6.2 × 10 3 mm 3 , normal level of hemoglobin 12.3 mg/dL, and elevated B-HCG > 50 000 mIU/mL. Informed consent was obtained, then an urgent diagnostic mini-laparotomy was performed, both fallopian tubes and ovaries were normal, a hemi-uterus with a left rudimentary non-ruptured pregnancy was found. There was no blood in the abdomen, and no endometriosis lesions were found (Figs 3 and 4 ). We removed the rudimentary horn with ipsilateral salpingectomy, and the left ovary was preserved. There was minimal blood loss, with no intra- or post-operative complications. Figure 3. The rudimentary horn on the left side connected to the uterus with a band of connective tissue (blue arrow). The ovaries on both sides are normal (red arrows). Figure 4. The gestational sac (blue arrow) and the left fallopian tube (black arrow). The rudimentary horn on the left side connected to the uterus with a band of connective tissue (blue arrow). The ovaries on both sides are normal (red arrows). The gestational sac (blue arrow) and the left fallopian tube (black arrow). The patient was examined for abnormalities in the urinary system; no deformation was found except mild bilateral hydronephrosis (Fig. 5 ). The period after the surgery was uneventful, and the patient was discharged the day after surgery in good general condition. Histopathology confirmed pregnancy in the rudimentary horn. Figure 5. The right and left kidneys, mild bilateral hydronephrosis. The right and left kidneys, mild bilateral hydronephrosis.

A unicornuate uterus is one of the Müllerian anomalies, representing 10% of these abnormalities [ 1 ] . It results from incomplete development of one of the Müllerian ducts and an incomplete fusion with the contralateral side [ 2 , 3 ] . Its prevalence in the general population is 0.1% [ 4 ] . The incidence of pregnancy occurring in a rudimentary horn of the unicornuate uterus is very rare, ranging from 1 in 76 000–160 000 pregnancies [ 5 ] , and is associated with life-threatening complications, such as uterine rupture with massive hemoperitoneum that occur at 10–15 weeks of gestation in most cases [ 6 ] . Therefore, a high index of suspicion is needed to make an earlier diagnosis using the prenatal ultrasonography, which will help in decreasing maternal morbidity and mortality. HIGHLIGHTS Unicornuate uterus with a rudimentary horn is type 2 of Müllerian duct anomalies. Pregnancy in the rudimentary horn of the unicornuate uterus is an uncommon presentation of an ectopic pregnancy. Timely diagnosis and management of ectopic pregnancy in the rudimentary horn is crucial in preventing its catastrophic complications and reducing maternal morbidity and mortality. Unicornuate uterus with a rudimentary horn is type 2 of Müllerian duct anomalies. Pregnancy in the rudimentary horn of the unicornuate uterus is an uncommon presentation of an ectopic pregnancy. Timely diagnosis and management of ectopic pregnancy in the rudimentary horn is crucial in preventing its catastrophic complications and reducing maternal morbidity and mortality. Here, we present a clinical case of a patient, who presented to our academic tertiary hospital (University Hospital of Obstetrics and Gynecology in Damascus), with an undiagnosed unicornuate uterus and an unruptured ectopic pregnancy in its rudimentary horn. The work has been reported in line with the SCARE criteria [ 7 ] .

Congenital uterine abnormalities, which are known as Müllerian duct anomalies (MDAs), arise from the abnormal formation, confluence, or resorption of the mesonephric (Müllerian) ducts during fetal life. The incidence of MDAs in the general population is estimated to be between 3% and 5% [ 1 ] . The etiology of these abnormalities is thought to be polygenic and multifactorial. The karyotype of patients is normal in most cases (46, XX) [ 8 ] . Failure of one Müllerian duct to develop and elongate results in a unicornuate uterus. This anomaly, which represents approximately 10% of MDAs, is the most contributing one to infertility [ 1 ] . With a unicornuate uterus, ipsilateral Müllerian structures are undergoing agenesis or, more frequently, a rudimentary uterine horn is identified [ 9 ] . Unicornuate uterus can be further subdivided into four variants according to the American Society of Reproductive Medicine (ASRM) classification 2021 (Fig. 6 ) [ 10 ] : Rudimentary horn with functional endometrium (A1) has two subtypes: Communicating subtype, in which the endometrial cavity of a rudimentary horn is in open communication with the uterus (A1a). Noncommunicating subtype, in which no open communication exists between the endometrial cavity of a rudimentary horn and uterus (A1b). Atrophic uterine remnant or no-cavity (A2) can be associated with the unicornuate uterus or distal from it. No-horn subtype, in which the ipsilateral fallopian tube (rudimentary horn) is absent (B). Figure 6. Classification of unicornuate uterus according to ASRM. Rudimentary horn with functional endometrium (A1) has two subtypes: Communicating subtype, in which the endometrial cavity of a rudimentary horn is in open communication with the uterus (A1a). Noncommunicating subtype, in which no open communication exists between the endometrial cavity of a rudimentary horn and uterus (A1b). Communicating subtype, in which the endometrial cavity of a rudimentary horn is in open communication with the uterus (A1a). Noncommunicating subtype, in which no open communication exists between the endometrial cavity of a rudimentary horn and uterus (A1b). Atrophic uterine remnant or no-cavity (A2) can be associated with the unicornuate uterus or distal from it. No-horn subtype, in which the ipsilateral fallopian tube (rudimentary horn) is absent (B). Classification of unicornuate uterus according to ASRM. Rudimentary horns are found in 74% of unicornuate uteri, and 70–90% of them are non-communicating horns (A1b) [ 11 , 12 ] . Unicornuate uterus is usually detected during the investigations of infertility, endometriosis, hematometra, dysmenorrhea, torsion of rudimentary horn, and obstetrical complications, like: spontaneous abortion, preterm delivery, malpresentation, fetal-growth restriction [ 13 ] . Pregnancy may also occur in the rudimentary horn, which is associated with a high rate of uterine rupture (typically prior to 20 weeks), and associated with a 0.5% maternal mortality rate regardless of its subtype [ 6 ] . In noncommunicating horns, this ectopic pregnancy seems to be occurred by transmigration of peritoneal sperm or fertilized ovum from the contralateral fallopian tube [ 14 ] . It has been described that rudimentary horn pregnancies are extremely rare and reported at 1:76 000–1:160 000 pregnancies [ 5 ] . Because of the closely related development of the genital and urinary tract, about 40–60% of the MDAs present with renal and ureteral abnormalities [ 11 , 15 ] . However, our case was not complicated with urinary system malformation, except for mild bilateral hydronephrosis that did not affect corticomedullary differentiation. Early diagnosis of MDAs can be easily missed due to a lack of awareness. So that various imaging modalities can be used as diagnostic tools. Ultrasonography, especially the transvaginal one, is frequently used in emergency or initial evaluations. Three-dimensional ultrasonography further increases the accuracy of diagnosis [ 16 ] . Nevertheless, the ultrasound sensitivity for diagnosis of rudimentary horn pregnancy ranges from 29% to 33% only, and decreases with advanced maternal age [ 11 , 17 ] . It would be helpful to use the three-sonographic criteria suggested by Tsafrir and his associates for the diagnosis of rudimentary horn pregnancy [ 18 ] : Pseudo pattern of asymmetrical bicornuate uterus. Absent visual continuity between the cervical canal and the lumen of pregnant horn. The presence of myometrium surrounding the gestational sac. Pseudo pattern of asymmetrical bicornuate uterus. Absent visual continuity between the cervical canal and the lumen of pregnant horn. The presence of myometrium surrounding the gestational sac. Sometimes, color Doppler ultrasonography reveals a vascular pedicle between the unicornuate uterus and the gestational sac in the rudimentary horn. Magnetic resonance imaging (MRI), though limited by expense and availability, remains the gold standard for diagnosing MDAs as it provides clear delineation of both the uterine cavity and its external contours. However, the diagnosis is sometimes missed even with MRI, because of the changeable position of unicornuate uterus and rudimentary horn. Hysterosalpingogram, hysteroscopy, and laparoscopy can be useful diagnostic tools [ 16 , 19 ] . In the case of this patient, the diagnosis of a rudimentary horn pregnancy was missed in the first antenatal ultrasound scan at 6 weeks of gestation. The ectopic pregnancy was only suspected when the patient presented to us with left iliac fossa tenderness, and ultrasonography using Tsafrir criteria was performed. Emergency mini-laparotomy confirmed the unruptured horn pregnancy. The surgical approach consists of the total excision of the symptomatic rudimentary horn and the removal of the ipsilateral fallopian tube in order to avoid the risk of a further ectopic tubal pregnancy. This could be easily performed by either laparotomy or laparoscopy, especially when the rudimentary horn is separated from the uterus [ 20 ] . It is also expected that this removal would prevent torsion of the rudimentary horn and neoplastic diseases [ 19 ] . In our case, we resected the rudimentary horn with its fallopian tube by laparotomy. The patient was discharged in good condition, with recommendations to prevent pregnancy for at least 6 months, and a C-section as a preferred mode of delivery in her next pregnancy. Due to a lack of evidence about delivery mode preferences after rudimentary horn excision, more research should be done. It is recommended not to delay surgery once the diagnosis of an unruptured ectopic pregnancy in a rudimentary horn is made because of the catastrophic complications that could happen [ 21 ] . In the case of confirmed rudimentary horn pregnancies with early gestational age, laparoscopic surgery, systemic methotrexate administration, or feticide with intracardiac potassium chloride have been recommended as alternatives to laparotomy [ 22 ] .

Pregnancy in a rudimentary uterine horn is an extremely rare condition, requiring a precise diagnosis and urgent intervention to prevent its serious complications, such as torsion, rupture, and massive hemoperitoneum. This case highlights the importance of increased awareness about Mullerian anomalies and their radiological features amongst healthcare providers, helping them in early detection and making appropriate decisions to reduce morbidity and mortality and maintain women’s health.