Unicornuate uterus is associated with appr. 90% non-communicating rudimentary horn (2). In the uterus with rudimentary horns, the rudimentary part is usually located on the right side. The reason for this is that the left müllerian canal moves caudally than right part (4). In our case too, the rudimentary horn was located on the the right. The rudimentary horn, which is not connected to the cavity-containing uterus, can cause retrograde menstruation, causing hemosalpinx and endometriosis from the same-sided fallopian tubes (5). In our case, endometriotic foci were observed on the pouch of Douglas and peritoneum. The majority of rudimentary horn pregnancy patients were admitted to the hospital -between the gestational weeks of 10th and 20th- with acute abdominal pain as a result of uterine rupture (6). In our case too, rudimentary horn pregnancy could not be diagnosed during routine follow-up and routine second-trimester ultrasonoghraphic scan, and the patient was admitted to the hospital with acute abdominal pain at 26th gestational weeks. The rudimentary horn was diagnosed by comparing the pre-operative and pre-pregnancy MRI scans, and the diagnosis was confirmed during the surgical procedure.
The rudimentary horn is hard to identify, especially if not suspected, and may be misdiagnosed as pelvic mass or cervix (7). When pregnancy develops in a rudimentary horn, the absence of continuity between the gestational sac’s lumen and the cervical canal on ultrasound is an important finding (8).
MRI allows accurate classification of unicornuate uterus. At MRI, the small, curved unicornuate uterus is typically displaced off midline. This appearance is named "Banana" configuration. It has normal myometrial zonal anatomy, with normal endometrial-to-myometrial width and ratio. The appearance of the rudimentary horn varies by subtype. If there is no endometrium present, zonal anatomy is absent and the entire horn may demonstrate diffuse low signal intensity. A rudimentary horn without endometrium and the absent rudimentary horn subtype present minimal risk and do not usually require surgical intervention. However, the presence of endometrium in a rudimentary horn is an important finding and should be reported. A non-communicating rudimentary horn with endometrium may manifest as a large uterine mass, endometriosis, and ectopic pregnancy. If endometrial tissue is present, there may be preserved zonal anatomy. After gadolinium injection; dominant and rudimentary horns show normal myometrial enhancement (9).
In our case, in pre-pregnancy ultrasound and MRI examinations; the rudimentary horn was followed with misdiagnosis as myoma. When we re-evaluated the old MRI images, rudimentary horn and zonal anatomy were clearly observed, especially in the coronal FS T2WI sequence (Fig. 2D). During pregnancy follow-ups, it was not noticed that the gestational sac was not continuous with the cervical canal on ultrasound. Preoperative MRI images revealed that the gestational sac was located separately from the normal uterine cavity (Fig. 1).
During surgery, same-sided salpingectomy -to avoid following ectopic pregnancies-, excising of the rudimentary horn is recommended. Oophorectomy is not recommended. Laparoscopy can be performed in non-ruptured cases (10). However laparotomy was preferred because our patient was with ruptured-rudimentary horn, was in an advanced gestational week, and was hemodynamically unstable. In addition, this anomaly is highly associated with - mostly same sided- urinary tract abnormalities (incidence found to be 36 percent) (11). The incidence of major renal anomalies associated with incomplete uterine duplication with non-communicating rudimentary horn varies between 31% and 100%. The most common anomaly is renal agenesis on the same side with non-communicating rudimentary horn, while the same-sided pelvic kidney is 2nd most common one. In our case, no urinary tract anomalies were found.