Why do niches develop in Caesarean uterine scars? Hypotheses on the aetiology of niche development

Caesarean section (CS) results in the occurrence of the phenomenon 'niche'. A 'niche' describes the presence of a hypoechoic area within the myometrium of the lower uterine segment, reflecting a discontinuation of the myometrium at the site of a previous CS. Using gel or saline instillation sonohysterography, a niche is identified in the scar in more than half of the women who had had a CS, most with the uterus closed in one single layer, without closure of the peritoneum. An incompletely healed scar is a long-term complication of the CS and is associated with more gynaecological symptoms than is commonly acknowledged. Approximately 30% of women with a niche report spotting at 6-12 months after their CS. Other reported symptoms in women with a niche are dysmenorrhoea, chronic pelvic pain and dyspareunia. Given the association between a niche and gynaecological symptoms, obstetric complications and potentially with subfertility, it is important to elucidate the aetiology of niche development after CS in order to develop preventive strategies. Based on current published data and our observations during sonographic, hysteroscopic and laparoscopic evaluations of niches we postulate some hypotheses on niche development. Possible factors that could play a role in niche development include a very low incision through cervical tissue, inadequate suturing technique during closure of the uterine scar, surgical interventions that increase adhesion formation or patient-related factors that impair wound healing or increase inflammation or adhesion formation.

Prenatal examination of the area and morphology of the atrioventricular valves using four-dimensional ultrasound in normal and abnormal hearts

OBJECTIVE

Our aim is to evaluate the feasibility to examine the morphology and area of the atrioventricular (AV) valves in normal fetuses and fetuses with cardiac defects using spatiotemporal image correlation (STIC).

METHODS

Atrioventricular valves were analyzed longitudinally in STIC volumes of 74 normal fetuses between the 15th and 36th week of pregnancy. The valve area was measured in a rendered view in diastole, the number of valve leaflets in systole. Longitudinal data analysis was performed using linear mixed models. Fifty fetuses with cardiac defects were examined.

RESULTS

Examination of 355 STIC volumes of normal fetuses showed in 82.5% sufficient quality. The tricuspid valve leaflets were seen in 200 (68.3%) volumes and the mitral valve leaflets in 219 (74.7%) volumes. The tricuspid valve showed in 61.1% a round, 29.0% rectangle, and 8.9% elliptical shape and the mitral valve in 60.1% round, 28.0% rectangle, and 10.9% elliptical. Regression analysis revealed a positive relationship of the valve area with gestational age (p < 0.0001). Most heart defects with stenosis showed an area below the 5th percentile.

CONCLUSION

Prenatal examination of the morphology and area of the AV valves using four-dimensional ultrasound is feasible. A rectangular valve opening is normal, which was visualized in about one third of the normal fetuses.

Differential insertion of the atrioventricular valves: measurement protocol to detect various congenital heart defects

OBJECTIVES

The objectives of this study were to develop reference values for the distance between the atrioventricular valves, called differential insertion of the atrioventricular valves (DIAVV), in normal fetuses using four-dimensional ultrasound with spatio-temporal image correlation and to explore if DIAVV measurement can differentiate between normal hearts and hearts with cardiac defects.

METHODS

The DIAVV was analysed longitudinally following a measurement protocol in 74 fetuses between 15 and 36 weeks gestational age. The DIAVV was measured in an apical four-chamber view of the heart in end-diastole. Furthermore, the DIAVV was measured in 70 fetuses with cardiac defects.

RESULTS

In total, 337 normal and 70 abnormal spatio-temporal image correlation volumes were examined. Longitudinal regression analysis revealed a positive relationship of the DIAVV with gestational age and fetal biometry (p < 0.0001). The DIAVV of fetuses with double outlet right ventricle, truncus arteriosus, atrioventricular septal defects, Ebstein and tetralogy of Fallot all differed from normal fetuses (p < 0.05).

CONCLUSION

Measurement of the DIAVV is a promising tool; however, a well-defined measurement protocol should be followed to accomplish the correct plane and exact moment in the cardiac cycle. This study presents new nomograms following this measurement protocol and reports an abnormal DIAVV in a wide spectrum of congenital heart disease.

Reliability of fetal cardiac volumetry using spatiotemporal image correlation: assessment of in-vivo and in-vitro measurements

OBJECTIVE

To assess the reliability of measurement of fetal cardiac ventricular volume, stroke volume, and ejection fraction with four-dimensional ultrasound using spatiotemporal image correlation (STIC).

METHODS

Volume datasets were collected from two sources: 24 from fetuses over a range of gestational ages and 12 from a miniature balloon model. Datasets were analyzed by three observers, repeatedly in 12 fetal datasets and all balloon datasets. Volume calculations were obtained by manually tracing multiple parallel slices (three-dimensional (3D) slice method). Measurement error was assessed by calculating standard errors of measurement (SEM) and coefficients of variation (CV). Reliability was assessed by calculating interobserver and intraobserver intraclass correlation coefficients (ICC).

RESULTS

Measurement errors of balloon volumes were small and reliability was good (SEM <or= 0.07 mL, ICC 0.98-1.00). Fetal ventricle volume measurement error ranged from 0.09 to 0.20 mL and CV from 14.6 to 28.3%. Ventricular volume reliabilities for intra- and interobserver comparisons were greater than or equal to 0.94 and 0.75, respectively. Fetal stroke volume measurement error (SEM 0.17 mL), CV (21.9%) and reliability were measured (intraobserver ICC: left ventricle stroke volume (LVSV), 0.93 vs. right ventricle stroke volume (RVSV), 0.88; interobserver ICC: LVSV, 0.75 vs. RVSV, 0.86). The measurement error decreased with increasing operator experience. The reliability of ejection fraction calculations was poor (ICC < 0.7) for intra- and interobserver comparisons.

CONCLUSIONS

Volume measurements obtained with STIC and 3D slice methods using a balloon model were reliable. In the fetus, measurement errors decreased with increasing operator experience, and reliability was better for stroke volume than for ejection fraction.

Validation of volume measurements for fetal echocardiography using four-dimensional ultrasound imaging and spatiotemporal image correlation

OBJECTIVES

To assess the accuracy and reliability of four-dimensional (4D) ultrasound imaging using spatiotemporal image correlation (STIC) employing three different techniques to measure volumes in vitro.

METHODS

Customized miniature balloons attached to a pump system were used to mimic fetal cardiac chambers. After the balloon model had been immersed in a bath filled with viscous gel, 4D datasets were acquired and three methods were used for volume analysis: three dimensional (3D) slice method, Virtual Organ Computer-aided AnaLysis (VOCAL) and VOCAL combined with inversion mode. Accuracy and measurement error were measured as the difference between the volume measurements and the actual volumes. Intraobserver reliability was assessed by computing coefficients of variation (CV) and intraclass correlation (ICC).

RESULTS

Measurement of 76 different volumes, ranging from 0.30 to 4.95 mL, resulted in a total of 912 measurements. The 3D slice method had a mean error of -3.3%, the inversion method underestimated the volumes with a mean error of -6.1%, and VOCAL had a mean error of -2.9%. The 3D slice method had the best agreement (95% limits of agreement (LOA), -11.2 to 4.7%), followed by VOCAL (95% LOA, -14.1 to 8.3%); the inversion mode demonstrated the worst agreement (95% LOA, -21.4 to 9.2%). All three methods were reliable with CV < 10% and ICC > 0.95.

CONCLUSIONS

4D ultrasonography with STIC is a feasible and accurate method for calculating volumes of 0.30 mL upwards. In an in-vitro model the 3D slice method proved accurate, was the least time consuming, had the best reliability and had the smallest LOA. This method may prove useful when applied to in-vivo investigations.

Fetal cardiac function assessed with four-dimensional ultrasound imaging using spatiotemporal image correlation

OBJECTIVES

The goal of this study was to use spatiotemporal image correlation (STIC) to provide reference values for left and right ventricle volumes, and indices of fetal cardiac function.

METHODS

In this prospective longitudinal study, STIC volumes were acquired periodically from 12 weeks of gestation onwards. The STIC volumes were frozen in end-systole and end-diastole, and volumetric data were measured by manual tracing and summation of multiple slices. These ventricle volumes were used to calculate stroke volume, ejection fraction and cardiac output.

RESULTS

Some 202 STIC volumes of 63 fetuses were included in the analysis. Mean left and right ventricle stroke volume increased from 0.02 mL at 12 weeks to 1.41 mL and 1.46 mL, respectively, at 30 weeks, while the mean right to left stroke volume ratio remained stable at around 1.2. Mean left and right ventricle cardiac output increased from 2.40 mL/min and 2.60 mL/min at 12 weeks to 197.74 mL/min and 204.81 mL/min, respectively, at 30 weeks. Both left and right mean ejection fraction remained constant at around 0.45 with advancing gestational age. Bland-Altman analysis showed a coefficient of variation for measured stroke volume of 13.7%.

CONCLUSIONS

This study establishes reference values for fetal cardiac volumes and indices for fetal cardiac function from 12 to 30 weeks of gestation using STIC. STIC seems to overcome many of the pitfalls of conventional ultrasound methods and has the potential to become the method of choice.

A systematic analysis of the feasibility of four-dimensional ultrasound imaging using spatiotemporal image correlation in routine fetal echocardiography

OBJECTIVES

To investigate the feasibility of incorporating spatiotemporal image correlation (STIC) into a tertiary fetal echocardiography program.

METHODS

During the study period all pregnant women fitting our inclusion criteria were enrolled consecutively. Four sonographers participated in the study, one of whom had substantial previous experience of STIC volume acquisition and three of whom did not. STIC volumes were acquired within the time slot allocated for the usual examination and all attempts were recorded. STIC volumes were assessed on acquisition conditions, the quality (as defined by a checklist of cardiac structures that could be visualized), and the rendering abilities. Furthermore, possible learning effects and the influence of experience with STIC on volume acquisition were studied.

RESULTS

STIC volume acquisition was successful in 75.7% (112/148) of cases in which it was attempted. The more experienced sonographer had a higher success rate in STIC volume acquisition (experienced vs. less experienced, 88.4% vs. 70.5%, P = 0.02). Of all analyzed STIC volumes, 64.8% were of high or sufficient quality. STIC volume quality and rendering ability correlated strongly with the acquisition conditions. High-quality STIC volumes successfully rendered the intracardiac septa in 84.6% of cases. The coronal atrioventricular plane was rendered in 12/26 cases (46.2%).

CONCLUSIONS

This study shows that incorporation of STIC volume acquisition into the daily practice of a tertiary fetal echocardiography program is feasible. Sonographers do not have to be specifically experienced in three- or four-dimensional ultrasound imaging to acquire high-quality STIC volumes. For successful STIC acquisition and subsequent successful analysis, correct acquisition conditions are of major importance. Finally, our results demonstrate that STIC is as susceptible as conventional two-dimensional ultrasound imaging to individual variations and limitations in scanning windows.