Original ContributionEvaluation of the Development of the Fetal Anal Sphincter with Tomography Ultrasonography Imaging
Introduction
Imperforate anus or anorectal atresia is a relatively common anomaly, with an incidence of 1:1500 to 1:5000 in newborns (Boocock and Donnai, 1987, Cho et al., 2001, Stoll et al., 1997). The survival rate of fetuses with imperforate anus is unfavorable, about 35% (Brantberg et al. 2006). Although the condition is generally treated by surgery neonatally, prenatal recognition of imperforate anus is important, because it is frequently associated with other congenital or chromosomal abnormalities, such as urinary and sexual dysfunction or trisomy 21 (Huisman and Kellenbegerer 2008). Improving prenatal diagnosis can aid in optimizing perinatal care and prenatal counseling (Black and Sherman 1989). Thus, the correct diagnosis of imperforate anus, although challenging, is highly important in prenatal diagnosis (Vijayaraghavan et al. 2011). Although reports have been published on the prenatal diagnosis of imperforate anus (Brantberg et al., 2006, Grant et al., 1990, Guzman et al., 1995, Harris et al., 1987, Lam et al., 2002, Taipale et al., 2005, Tiblad et al., 2008, Vasudevan et al., 2006), it is usually underdiagnosed until after birth. However, the low rates of visualization of the fetal anal sphincter and correct prenatal diagnosis of imperforate anus may result from insufficient knowledge of the normal sonographic appearance of the fetal anal sphincter. It is possible that if nomograms of the normal fetal anal sphincter were created and the anatomy was evaluated with reference to these parameters, the rate of detection of lesions involved in this system would improve.
Three-dimensional ultrasonography (3-DUS) has been used to evaluate the adult anal sphincter (Dietz, 2004, Valsky et al., 2007). We explored the application of tomography ultrasonography imaging (TUI) of 3-DUS to examination of the fetal anal sphincter. In our experience, prenatal TUI identification of the fetal anal sphincter is now possible routinely.
Our aim, therefore, was to investigate the capability of TUI in evaluating development of the normal fetal anal sphincter and provide reference values for prenatal diagnosis of imperforate anus.
Section snippets
Methods
In this prospective cross-sectional study of the fetal anal sphincter with TUI, 326 singleton pregnancies (mean age = 28 y, range: 22–38 y) were scanned at 19–40 wk of gestation. Gestational age (GA) was calculated from the first date of the last menstrual period (LMP) and confirmed by first-trimester ultrasound measurements of fetal crown–rump length. The study was performed in an ultrasonography department over a period of 2 y. The enrollment criteria in this study were as follows: (i)
Results
A total of 326 consecutive women who met the inclusion criteria were enrolled in the study. However, evaluation of 6 fetuses was not possible because of suboptimal position or early GA. Therefore, a total of 320 fetuses were included with a visualization rate of the fetal anorectal area and ischium of 98.2%. The age range of the pregnant women was 22 to 38 y, with a mean maternal age of 28 ± 4 y. The fetal anal sphincter was visualized in 319 fetuses but not in 1 fetus. Normal fetal anal
Discussion
We have described a TUI method for imaging the fetal anal sphincter. We created scatterplots of normal fetal sphincter diameter and ischial space by GA. A scatterplot created revealed a significant positive relationship between normal fetal anal sphincter diameter and ischial space.
Previously, most reports on the prenatal diagnosis of imperforate anus have focused on sonographic identification of a dilated distal bowel or rectum (Kaponis et al. 2006). Harris et al. (1987) achieved prenatal
Conclusions
Ultrasonographic assessment of the fetal anal sphincter and the fetal ischium with TUI is feasible. Data from our study revealed linear growth of the fetal anal sphincter and the ischial space over the course of pregnancy. We also found a significant positive relationship between normal fetal anal sphincter diameter and ischial space, which can be used to evaluate development of the fetal anal sphincter. The reference values reported in this article may be useful in prenatal diagnosis of fetal
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