The embryology of uterus bicornis with a rudimentary horn is a consequence of the failure of progression of one of the two Müllerian ducts between the sixth and ninth week of gestation. This rudimentary horn may have a cavity with endometrial lining of the uterus, and thus can serve as a site of implantation during pregnancy [1] [2] . Pregnancy in a rudimentary horn usually results in its rupture which can lead to a life-threatening heavy bleeding. That is an extremely rare condition 10-fold less common than abdominal pregnancy [3] . We describe a clinical case of a rupture of the rudimentary horn which occurred at 25 weeks of amenorrhea.

An unmarried 19-year-old primigravida was referred to our service for persistent abdominal and pelvic pain. During this pregnancy, she had never attended any antenatal care service. Clinical examination showed a stable gene- ral condition with blood pressure 100/60 mm Hg and pulse at 88 beats/min. The abdomen was slightly distended and sensitive with dullness in both flanks. Vaginal examination disclosed a single softened closed cervix without bleeding. The first ultrasound examination was performed and suspected an abdominal pregnancy of 25 weeks with fetal death. There were no signs of peritoneal effusion. During hospitalization, she presented peritoneal effusion syndrome with signs of shock. The patient was taken for emergent laparotomy, which revealed 300 ml of blood and a deceased but morphologically normal fetus weighing 610 free in the abdominal cavity. After inspection, we discovered a rupture of the upper surface of a rudimentary left horn of a uterus bicornis unicollis. The left fallopian tube and the left ovary appeared normal and were connected on this rudimentary horn. The rudimentary horn was removed by clamping, ligating and cutting its attachment to the right horn. The postoperative course was uneventful and the patient was able to leave the hospital on post-operative day 7 (Figure 1 and Figure 2).

Mauriceau described the first case of uterine rupture during pregnancy in a rudimentary horn in 1669 [4] . This report is the first case documented in our department at the Teaching Hospital of Cocody. According to 47 studies of 570,000 women, the incidence of uterine malformations is 0.5%, and of these, 5% are horned uterus [1] . The incidence of rudimentary horn pregnancy is estimated at 1/100,000 to 1/140,000 [2] . Ten percent of these rudimentary horns

communicate with the main uterine horn and 35% have a cavity [1] . There is a slight predominance of the rudimentary horn at the right side potentially related to the more caudal location of the left Müllerian duct [4] . The implantation of the egg in the aplastic horn is usually the result of transperitoneal migration of a spermatozoid to the rudimentary horn. Since the elasticity of the horn is limited, the risk of its rupture during pregnancy is high. This can occur early in the second trimester [5] .

Diagnosis of pregnancy in a uterine horn is difficult owing to the non-specific nature of the symptoms, mainly severe abdominal pain in the second trimester. The differential diagnosis might include ectopic, corneal or isthmic pregnancy [6] . It is associated with intraperitoneal hemorrhage, which can be revealed by ultrasound examination. Rupture frequently leads to emergency surgery, at which point a diagnosis is typically established [7] . Laparoscopy may be a reasonable approach in uncertain circumstances. Earlier detection of uterine malformations by ultrasound or magnetic resonance imaging (MRI) examination may be useful to prevent this devastating obstetrical accident which can lead to maternal mortality [8] .

When uterus bicornis with rudimentary horn is discovered incidentally without pregnancy, the rudimentary horn should be excised when possible. This procedure can be performed using a laparoscopic approach [9] [10] . If pregnancy in a rudimentary horn is diagnosed in the first trimester, it may be reasonable to continue the pregnancy with ultrasound monitoring close to a term of 28 weeks to allow for fetal lung maturation. Surgical intervention can be performed when the estimated fetal mass is greater than 1000 grams or if the thickness of the myometrium at any point of the wall is less than 5 mm [5] .

Fewer than 5% of cases are recognized before laparotomy must be performed for hemorrhagic shock [11] . These pregnancies are also at risk of placenta accreta and percreta, probably because of the poor quality of the endometrium and low decidualization [11] [12] . In a series of 7 pregnancies implanted in the uterine rudimentary horn, Heinonen [13] noticed three cases of placenta accreta (43%), which was also favored by pathological examination of our case. In settings with limited access to health care resources, this condition could lead to maternal death.

Early diagnosis of a rudimentary horn pregnancy is usually accidental. Ultrasound examination may be a useful tool to detect these pregnancies in the first trimester. Abdominal pain occurring in the second trimester of pregnancy without identified cause should alert the clinician to this condition, and ultrasound examination will diagnose an intraperitoneal hemorrhage. Undiagnosed, this condition evolves towards uterine rupture and requires emergency surgery with excision of the rudimentary horn.

The patient had given her consent for the reported case to be published.

Didier, K.A., Roland, A.C., Joachim, K., Dénis, E.N., KakouChales, Alice, D.F., Victor, K.S. and Firmin, K. (2017) Rupture of a Rudimentary Uterine Horn: A Case Report. Open Journal of Obstetrics and Gynecology, 7, 748-752. https://doi.org/10.4236/ojog.2017.77076