although uterine rotation due to a myoma is a rare complication of pregnancy 1 , obstetricians should be alerted to avoid making an incorrect uterine incision during cesarean section . a 35-year - old woman ( gravida 1 , para 0 ) was referred to our hospital for delivery because her pregnancy was complicated by a left - sided myoma that measured 15  cm in diameter during ultrasonography .
the patient 's medical history included renal artery aneurysm , primary aldosteronism , and chronic hypertension . to determine the anatomical relationship between the uterus and the myoma , we performed magnetic resonance imaging ( mri ) at 30  weeks ' gestation ( fig.1a ) .
mri revealed that the myoma was intramural and located on the left side . notwithstanding the myoma ,
the pregnancy had not been complicated by abdominal pain , placental abruption , fetal growth restriction , or preterm labor and birth .
fetal growth was determined to be appropriate for the gestational age , and no major anomalies were revealed by ultrasound . because of breech presentation , the patient was scheduled to undergo an elective cesarean section .
owing to her chronic hypertension , the cesarean section was scheduled for 37  weeks ' gestation .
( a ) magnetic resonance imaging revealed an intramural myoma on the left side ( its greatest dimension is not shown in this figure ) ; however , imaging did not reveal the degree of uterine rotation .
( b ) midline laparotomy showed multiple large vessels pressing on the uterus . from the first abdominal incision
prior to delivery , the obstetrician was unable to accurately understand the anatomical relationship between the myoma and the intra - abdominally placed uterus .
therefore , the abdominal incision was extended vertically around the umbilicus , and the uterus was brought outside the abdominal cavity ( fig.2a ) . as a result , we were able to evaluate the spatial relationship between the tumor and the uterus .
we then located the vessels belonging to the utero - ovarian ligament and the uterine parametrium ; they were facing front because the myoma had rotated the uterus 90. a vertical uterine incision was made to open the uterus ( fig.2b ) .
intraoperative bleeding was 1600  ml . we managed the section successfully , and the patient delivered a healthy male infant , weighing 2538 g with apgar scores of 4 and 9 at 1 and 5  min , respectively .
the neonate had no feeding - related complications ; he gained sufficient weight and was discharged with his mother .
six months after delivery , the patient 's myoma had decreased to approximately 11  cm in size . ( a ) by bringing the uterus outside the abdominal cavity during the cesarean section , we were able to determine that the uterus was rotated 90 by the myoma , and the right side of the uterus was anteriorly directed .
in this figure , the rotation has been corrected ; the white arrow denotes the area shown in figure1b .
( b ) because a low transverse uterine incision was not feasible , a vertical uterine incision was made . at the time of incision
, we monitored the surgical margin between the incision and the myoma to ensure that the myoma was maintained in order to prevent hemorrhage .
the distance between the incision and myoma usually shortens because of postdelivery uterine contraction . in summary , if the obstetrician has difficulty in confidently identifying the anatomical landmarks required to properly orient the uterine incision during a cesarean section , he or she should bring the patient 's uterus outside the abdomen .
if an ill - placed uterine incision is made to deliver the child , massive intraoperative hemorrhaging can result .
the authors declare that they have no conflicts of interest or funding disclosures related to this study .
 key clinical messagein pregnancies complicated by large myomas , obstetricians may face difficulties during cesarean section if they fail to notice the rotation of the uterus and could make an incorrect uterine incision 
 . this error might cause massive intraoperative hemorrhage . 
 obstetricians must exercise extreme caution during cesarean sections complicated by large myomas . 
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