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Detection of Cesarean Scars by Transvaginal Ultrasound

From the Department of Obstetrics and Gynecology, Harris Methodist Fort Worth Hospital, Arlington, Texas; and Department of Obstetrics and Gynecology, University of Iowa Hospitals and Clinics, University of Iowa, Iowa City, Iowa.

Address reprint requests to: Craig H. Syrop, MD, University of Iowa Hospitals and Clinics, Department of Obstetrics and Gynecology, Division of Reproductive Endocrinology, Iowa City, IA 52242-1080; E-mail: craig-syrop{at}uiowa.edu.

	ABSTRACT

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OBJECTIVE: To assess the ability of transvaginal ultrasound to detect cesarean scars and their defects in the nonpregnant state.

METHODS: Asymptomatic, parous volunteers underwent transvaginal ultrasound of the cervix, uterus, and adnexa. Uterine measurements, the presence or absence of a cesarean scar, and the presence of a scar defect, defined as fluid within the scar, were recorded. All subjects completed a self-report questionnaire regarding obstetric history. Sonographers and investigators were blinded to subject history.

RESULTS: A total of 70 subjects were enrolled. Of these, 38 women had a prior vaginal delivery and 32 women a prior cesarean delivery. One woman with a bicornuate uterus and three cesarean deliveries was excluded from data analysis. Real-time transvaginal ultrasound proved 100% sensitive (exact 95% confidence interval [CI] 88.8, 100) and 100% specific (exact 95% CI 90.7, 100). Stored image review had a sensitivity of 87% (exact 95% CI 70.2, 96.4) and a specificity of 100% (exact 95% CI 90.7, 100). Fluid was visualized within the scars of 13 of 31 subjects (42%) with a prior cesarean delivery. All 13 were found among the 23 subjects (56%) who had labored prior to cesarean delivery. Moreover, women with cesarean scar defects had a greater number of cesarean deliveries (P < .04) than women without scar defects.

CONCLUSION: Transvaginal ultrasound is highly accurate in detecting cesarean hysterotomy scars. Cesarean scar defect, defined by the presence of fluid within the incision site, was more common when labor preceded cesarean delivery and with multiple cesarean deliveries.

Cesarean scar defects have long been recognized in hysterosalpingograms as anterior out-pouchings.¹ The increasing use of transvaginal ultrasound and sonohysterography has allowed more frequent identification of these defects. Several investigators have reported an association between these defects and abnormal bleeding.^2–4 The ability of transvaginal ultrasound to detect cesarean scars remains unknown, as only symptomatic individuals were previously studied. This study investigated the ability of transvaginal ultrasound to detect cesarean scars and the prevalence of scar defects in asymptomatic, nonpregnant subjects. Prior studies have demonstrated that sonographic detection of fluid collections in the lower uterine segment are associated with histologically confirmed defects in the uterine scar.^2,3 Therefore, we defined a cesarean scar defect as the sonographic demonstration of fluid within the scar.

	MATERIALS AND METHODS

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This study was approved by the University of Iowa Institutional Review Board. Advertisements were placed in local newspapers, hospital newsletters, and the Gynecology Clinic. Two separate advertisements were titled: "Have you had one or more cesarean sections?" or, for the normal volunteers, "Have you had one or more vaginal deliveries?" Each subheading then stated: "Volunteers are invited for an ultrasound study of the cervix. If you have been pregnant and delivered, are between ages 18 and 40 and have delivered within the last five years, you can participate. Please contact . . . ." Subjects completed a brief questionnaire regarding obstetric history. Parous subjects without a history of cesarean delivery served as the control group. Each subject underwent a transvaginal ultrasound of the cervix, uterus, and adnexa (Sequoia 7–10 MHz, Acuson, Mountain View, CA) performed by one of two experienced sonographers blinded to the woman’s history. Women not taking exogenous hormones were scheduled for examination during cycle days 8–11. Detection of a cesarean scar by sonography begins with visualization of a hyperechoic, linear density through the stroma near the level of the internal os extending to the vesicouterine interface in the sagittal plane. Often the hyperechoic density spreads laterally. At times, a wedge-like defect (hyperechoic) is seen at the vesicouterine interface pointing toward the endocervical canal. Importantly, a scar defect will display a fluid collection along this line and in continuity with the endocervical canal.

Nabothian cysts are commonly seen in the stroma of the cervix. They vary in size, are round, anechoic, extremely thin-walled, and are most often adjacent to the endocervical canal closer to the external os. Potential differentiation of a stromal nabothian cyst from a scar defect should rest upon location (anterior surface) and knowledge of the pathophysiology of nabothian cysts. Because nabothian cysts occur as a result of reparative changes and obstruction of the endocervical glands, one would not expect sonographic visualization of fluid extending from the endocervical canal through the stroma and into the cystic collection of a nabothian cyst.

Cesarean scars were recorded as either present or absent. Cesarean scar defects were measured in two dimensions in the sagittal plane (anterior–posterior and cephalad–caudal) and transversely in the coronal plane. The maximal diameter in the sagittal view was used for comparison. The frequency of scar identification, as well as the presence of fluid within the scar ("scar defect"), was recorded and later compared with self-reported obstetric history. Photo documentation included a cervical view with presence or absence of a cesarean delivery scar and presence or absence of fluid within the scar (Figure 1). Additional images of endometrial stripe thickness, presence or absence of polyps or myomas, and ovarian volumes were recorded. All stored ultrasound images were reviewed independently by a single investigator (CHS), who was also blinded to patient history and sonographer assessments. Each subject was assigned a study number on entry. Data obtained from the questionnaires and from ultrasound were entered separately.

View larger version (118K): [in this window] [in a new window]   Figure 1. (Top) Fluid in a subtle cesarean scar defect after cesarean delivery. Down arrow indicates scar defect; up arrow indicates endocervical canal. (Bottom) Fluid in a large cesarean scar defect (nonstudy). Down arrow indicates scar defect; up arrow indicates endocervical canal; left arrow indicates anterior cervix. Armstrong. Ultrasound of Cesarean Scars. Obstet Gynecol 2003.

	RESULTS

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A total of 70 parous women were enrolled in the study. Of these, 32 subjects had experienced a cesarean delivery; 38 women with a history of only vaginal deliveries acted as controls. Twenty-three subjects had one prior cesarean delivery, five had two prior cesarean deliveries, and three had three or more cesarean deliveries. Only one subject had four or more cesarean deliveries. One patient with a bicornuate uterus had one cesarean delivery on the left and two on the right. Although scars were correctly identified on both sides, her data is excluded from statistical analysis for lack of independence. There was no significant difference in age, onset of menarche, cycle length, or parity between the two groups (Table 1). Using real-time ultrasound, sonographers identified cesarean scars in 100% of women with prior cesarean deliveries, and no women in the control group were classified incorrectly. The sensitivity (exact 95% confidence interval [CI] 88.8, 100) and specificity (exact 95% CI 90.7, 100) was 100% for real-time transvaginal ultrasonography.

Of 31 subjects, 13 (42%) demonstrated a cesarean scar defect as evidenced by fluid within the hysterotomy site. Only subjects who experienced labor prior to their cesarean delivery showed evidence of a cesarean scar defect (P = .01) (Table 2). Moreover, women with cesarean scar defects had a greater number of cesarean deliveries (P < .04). All defects measured less than 10 mm in maximal sagittal diameter.

	DISCUSSION

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That same year, Thurmond et al, in a retrospective study, reported that 9 of 310 women who presented for sonohysterography for abnormal bleeding demonstrated gaps in the anterior lower uterine segment myometrium at the expected site of the prior cesarean scar.³ Defects measured 8–17 mm in maximal diameter and were difficult to discern by transvaginal ultrasound alone. Two of the nine women ultimately underwent hysterectomy. Pathology revealed an evagination lined with normal endometrium.

More recently, Monteagudo et al reported a prospective observational study of 44 symptomatic women who underwent sonohysterography for a gynecologic indication (75% abnormal bleeding).⁴ All women had had at least one previous cesarean delivery. A triangular anechoic filling defect in the anterior wall of the uterus between the corpus and the cervix at the expected site of the cesarean scar was seen in all women. They called this defect a uterine "niche." Overall, the niches measured 6.2 ± 3.6 mm (mean and standard deviation). The largest niche was 11.5 mm deep, and the smallest was 2.5 mm. They found no correlation between the number of cesarean deliveries and the size of the niche. They were only able to identify a niche in 14 of the 44 women by ultrasound alone but stated that this improved over time as they gained experience.

Our study investigated the ability of transvaginal ultrasound to detect cesarean scars and their defects in asymptomatic women. When self-reported obstetric history was correlated with ultrasound findings, prolonged labor prior to cesarean delivery and multiple cesarean deliveries were associated with scar defects. Study design did not allow confirmation of the patients’ history, as many of the participants had delivered elsewhere and their medical record was not available to us. Our inability to confirm labor prior to cesarean delivery and the type of cesarean scar, low transverse or vertical, is a weakness of the study.

The sizes of the defects in our study group were smaller than those reported by others. Comparing sizes between studies is difficult because of the many variables affecting size, including the measurement technique, which was different in each study. Our smaller size may reflect our study population, in that small defects may be asymptomatic, whereas larger defects may cause abnormal bleeding. The defect seen on transvaginal ultrasound alone may appear smaller than the defect seen on sonohysterography once saline has distended the defect. It is also possible that visualization of defects may vary by menstrual cycle phase or use of exogenous hormones. Although we did not control for hormonal therapy, we did schedule ultrasound examinations between cycle days 8 and 11.

Do these cesarean scar defects have any obstetric significance? The scarred lower uterine segment has become one of the most controversial subjects in obstetrics as a public health effort to reduce the cesarean delivery rate confronts our better understanding of risk with a vaginal birth after cesarean. The scarred lower uterine segment is the most common reason for cesarean delivery. A recent, large, population-based retrospective review reported a uterine rupture rate ranging from 5.2 per 1000 with the spontaneous onset of labor to 24.5 per 1000 with the induction of labor with prostaglandins.⁵

In 1996, Rozenberg et al published a prospective, observational study of 642 women with a previous cesarean delivery undergoing ultrasound measurement of the lower uterine segment thickness between 36 and 38 weeks’ gestation.⁶ Their objective was to evaluate the relationship between lower uterine thickness and risk of uterine rupture or dehiscence. The managing obstetrician was blinded to the measurement. They found an overall frequency of defective scars of 4.0% (15 ruptures and 10 dehiscences). The frequency of defects rose significantly as the thickness decreased. Using a cutoff value of 3.5 mm, a sensitivity of 88%, a specificity of 73.2%, a positive predictive value of 11.8%, and a negative predictive value of 99.3% were achieved.

It is becoming increasingly clear that cesarean scar defects may be a cause of abnormal bleeding; however, their clinical significance in asymptomatic women remains unclear. Do they represent a weakened area of the scar? Are they a result of a single-layer closure as opposed to a more traditional two-layer closure? Are they a result of including endometrium in the incision closure? Are they normal variants that only become symptomatic and potentially harmful as they increase in size? Can we make any inferences from a sonographic defect in the nonpregnant state to an obstetric population at risk for uterine rupture during a trial of labor? Can ultrasound individualize the risk of a woman desiring a trial of labor after cesarean? Unfortunately, our current knowledge base does not allow us to draw extensive conclusions, but it does pose some intriguing questions. Transvaginal ultrasound holds promise as a useful tool for trying to answer these important clinical questions in prospective trials.

	Footnotes

 
PII S0029-7844(02)02450-X

Received April 22, 2002. Received in revised form June 21, 2002. Accepted July 18, 2002.

	REFERENCES

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1. Thurmond AS. The cervix and uterus. In: Thurmond AS, Jones MK, Cohen DJ, eds. Gynecologic, obstetric, and breast radiology. Cambridge, UK: Blackwell Science, 1996: 49.

2. Erickson SS, Van Voorhis BJ. Intermenstrual bleeding secondary to cesarean scar diverticuli: Report of three cases. Obstet Gynecol 1999;93:802–5.[Abstract/Free Full Text]

3. Thurmond A, Harvey W, Smith S. Cesarean scar as a cause of abnormal vaginal bleeding: Diagnosis by sonohysterography. J Ultrasound Med 1999;18:13–6.[Abstract]

4. Monteagudo A, Carreno C, Timor-Tritsch IE. Saline infusion sonohysterography in nonpregnant women with previous cesarean delivery: The "niche" in the scar. J Ultrasound Med 2001;20:1105–15.[Abstract]

5. Lydon-Rochelle M, Holt VL, Easterling TR, Martin DP. Risk of uterine rupture during labor among women with a prior cesarean delivery. N Engl J Med 2001;345:3–8.[Abstract/Free Full Text]

6. Rozenberg P, Goffinet F, Phillippe HJ, Nisand I. Ultrasonographic measurement of lower uterine segment to assess risk of defects of scarred uterus. Lancet 1996;347: 281–4.[Medline]

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