* Service de Gynécologie-Obstétrique, Hôpital Félix Guyon, Saint-Denis de La Réunion, France.

** Inner Vision Women's Ultrasound, Nashville, Tennessee, USA.

Introduction

Ultrasound evaluation of the lower uterine segment in pregnant women with a previous cesarean section is an important part of the prenatal ultrasound examination. It requires special attention in case of an attempted vaginal birth after cesarean section. Uterine rupture is a serious, life threatening condition to both mother and fetus.The use of ultrasound to evaluate the thickness of the myometrium of the uterine scar helps to forewarn  this potential risk. Failing of scarring means that only 1/3 of the surface layers of myometrium is healed and 2/3 of deeper myometrium layer remain dehiscent. The ultrasound demonstrates the uterine scar length, depth and wideness of the notch between two edges of the scar defect. According to studies1-2, the risk of uterine rupture during the trials of labor, is related to the degree of the thinning of the lower uterine segment. The technique of the uterine scar thickness measurement varies. Some studies measure only the thickness of the myometrium and some the full lower uterine segment thickness. The Montreal study suggested, that the combination of single-layer closure and full lower uterine segment thickness under 2.3 mm is related to a very high risk of uterine rupture.

A 35-year-old G5 P4, was referred to our antenatal unit at 29 weeks of gestation for the ultrasound finding of the uterine scar dehiscence. Patient  had a history of 4 cesarean sections. The amount of the amniotic fluid was normal. The fetus did not show any signs of the growth restriction. The first trimester screening and triple test were both normal, as well as the ultrasound scan performed at 24 weeks of gestation. On the ultrasound, we could see a very thin uterine scar with the typical notch in the myometrium. A herniation of the amniotic sac appeared through the scar dehiscence, during the contraction.

The patient was admited to the hospital and tocolytic therapy was initiated.

Patient delivered via elective cesarean section at 36 weeks of gestation. During the surgery, we found a very thin uterine scar with complete dehiscence of the myometrium. The only layer which covered the scar was perimetrium through which we clearly saw the baby's head. A tubal ligation was performed during the surgery to prevent any following pregnancy and a risk of the uterine rupture.

Images 1,2: Images show a uterine scar defect. Arrow indicates a notch in the myometrium which is caused by a dehiscent myometrium. Note an apparent thinning of the uterine wall on the image 2.

Images 3,4: Images show uterine scar during the contraction, note the herniation of the uterine scar.

Case report #2

This is a case of a 32-year-old G4P3 with a history of 3 cesarean sections. Patient was referred for the ultrasound scan due to a cervical incompetence. We scanned her at 27 weeks and found a notch in the myometrium at the level of the uterine scar.

We saw a complete dehiscence of the myometrium during the contraction. Patient was hospitalized due to a risk of premature labor and started on tocolytic therapy. She was at 31 weeks of gestation at the time we prepared this article.

Images 5,6,7: Images show myometrial notch.

Images 8,9: Images taken during the uterine contraction showing the dehiscent myometrium, the width of the defect measuring 20.9 mm.

Case report #3

This is a case of 27-year-old G3P2 who had 2 previous cesarean sections. There was a myometrial notch seen on the anterior uterine wall. The thickness of the muscular layer was 4.1 mm. The patient delivered at term via cesarean section. There was a remarkable thinning of the uterine scar but not a complete dehiscence.

Images 10-13: Images showing a defect of the uterine scar.

Case report #4

This is a case of 29-year-old G3P2 who had 2 previous cesarean sections. The ultrasound examination at 30 weeks showed a notch in the myometrium. The thickness of the muscular layer was 2.1 mm.  The subsequent ultrasound perfomed at 26 weeks showed the similar finding. The patient had a preterm delivery via cesarean section at 30 weeks of gestation. There was a very thin uterine scar, which confirmed our ultrasound finding.

Images 14,15: 23 weeks of gestation, arrow indicates the notch.

Images 16,17: 26 weeks of gestation, the thickness of the myometrium is only 2 mm.

Case report #5

This is a case of a 32-year-old G5P4 who had 4 previous cesarean sections. We performed the ultrasound examination at 31 weeks. There was a wide defect of the myometrium. The thickness of the myometrium was only 1,5 mm. Patient delivered at 38 weeks via cesarean section. The surgeon reported that there was a complete dehiscence at the level of the uterine scar, it was covered only with thin, see-through layer of perimetrium.

Images 18-21: Ultrasound images show the defect of the anterior uterine wall, the width of the defect is 14.4 mm.

References:

1. Cheung VYT, Constantinescu OC, Ahluwalia BS. Lower uterine segment in patients with previous cesarean delivery. J Ultrasound Med 2004; 23:1441-1447.