In-utero development of the fetal anal sphincter

Infracoccygeal/transperineal window: new method to prenatally diagnose and classify level of anal atresia

OBJECTIVES

To introduce a two-dimensional sonographic method to assess the fetal anus, and to evaluate the feasibility of this method to diagnose anal atresia prenatally and identify the presence or absence of anoperineal fistula (in males) and anovestibular fistula (in females).

METHODS

This was an observational study of suspected cases of anal atresia referred to a single center in Israel between August 2018 and October 2023. In addition to conventional evaluation of the perineum in the axial plane, fetuses referred to our center for suspected malformation were scanned with a new method termed the 'infracoccygeal/transperineal window'. This window consisted of a midsagittal view of the fetal pelvis, including the distal rectum and the anal canal. Normal anatomy was confirmed when the anal canal was continuous with the rectum and terminated at the expected location on the perineum. In female fetuses, the normal anal canal runs parallel to the vaginal canal and diverges posteriorly, terminating at the perineal skin, distant from the vestibule. In male fetuses, the normal anal canal diverges posteriorly in relation to the corpora cavernosa, terminating at the perineal skin, distant from the scrotum. High anal atresia was identified when a blind-ending rectal pouch was demonstrated in the pelvis without a fistula to the perineum or vestibule. Low anal atresia was determined when a rectal pouch was continuous with an anteriorly deflected fistula. In females, the fistula converges with the vaginal canal, terminating at the vestibule; in males, the fistula deflects anteriorly, terminating at the base of the scrotum. Postnatally, the diagnosis and type of anal atresia were confirmed through physical examination with direct visualization of the fistula, radiographic studies, surgical examination and/or postmortem autopsy.

RESULTS

Of the 16 fetuses diagnosed prenatally with anal atresia, eight were suspected to have low anal atresia and eight were suspected to have high anal atresia. The median gestational age at diagnosis was 23 (range, 14-37) weeks. All cases showed additional structural malformation. Eleven patients opted for termination of pregnancy, of which four had low anal atresia and seven had high anal atresia. Postnatal confirmation was not available in four cases due to curettage-induced mutilation or in-utero degradation following selective termination of the affected twin, leaving 12 cases for analysis, of which seven were diagnosed with low anal atresia and five with high anal atresia. In these 12 cases, all prenatal diagnoses were confirmed as correct, rendering 100% sensitivity and 100% specificity in this high-risk fetal population.

CONCLUSIONS

The infracoccygeal/transperineal window is an effective method to detect and classify the level of anal atresia prenatally. This may improve prediction of postnatal fetal continence and optimize prenatal counseling. © 2024 International Society of Ultrasound in Obstetrics and Gynecology.

Meconium-stained amniotic fluid

Green-stained amniotic fluid, often referred to as meconium-stained amniotic fluid, is present in 5% to 20% of patients in labor and is considered an obstetric hazard. The condition has been attributed to the passage of fetal colonic content (meconium), intraamniotic bleeding with the presence of heme catabolic products, or both. The frequency of green-stained amniotic fluid increases as a function of gestational age, reaching approximately 27% in post-term gestation. Green-stained amniotic fluid during labor has been associated with fetal acidemia (umbilical artery pH <7.00), neonatal respiratory distress, and seizures as well as cerebral palsy. Hypoxia is widely considered a mechanism responsible for fetal defecation and meconium-stained amniotic fluid; however, most fetuses with meconium-stained amniotic fluid do not have fetal acidemia. Intraamniotic infection/inflammation has emerged as an important factor in meconium-stained amniotic fluid in term and preterm gestations, as patients with these conditions have a higher rate of clinical chorioamnionitis and neonatal sepsis. The precise mechanisms linking intraamniotic inflammation to green-stained amniotic fluid have not been determined, but the effects of oxidative stress in heme catabolism have been implicated. Two randomized clinical trials suggest that antibiotic administration decreases the rate of clinical chorioamnionitis in patients with meconium-stained amniotic fluid. A serious complication of meconium-stained amniotic fluid is meconium aspiration syndrome. This condition develops in 5% of cases presenting with meconium-stained amniotic fluid and is a severe complication typical of term newborns. Meconium aspiration syndrome is attributed to the mechanical and chemical effects of aspirated meconium coupled with local and systemic fetal inflammation. Routine naso/oropharyngeal suctioning and tracheal intubation in cases of meconium-stained amniotic fluid have not been shown to be beneficial and are no longer recommended in obstetrical practice. A systematic review of randomized controlled trials suggested that amnioinfusion may decrease the rate of meconium aspiration syndrome. Histologic examination of the fetal membranes for meconium has been invoked in medical legal litigation to time the occurrence of fetal injury. However, inferences have been largely based on the results of in vitro experiments, and extrapolation of such findings to the clinical setting warrants caution. Fetal defecation throughout gestation appears to be a physiologic phenomenon based on ultrasound as well as in observations in animals.

First trimester lower abdominal cysts as early predictor of anorectal malformations

INTRODUCTION

Prenatal ultrasound diagnosis of anorectal malformations (ARMs) is challenging and often missed as direct visualization of the anal sphincter is not routinely performed, plus the technique is operator-dependent and inaccurate, also in expert hands. Other indirect signs, such as rectosigmoid overdistension or intraluminal calcifications, are occasionally present in late pregnancy. The detection of a cyst of the lower abdomen in the first trimester may be an early sign of ARM. Here we reported our experience and a review of the literature of such cases.

MATERIAL AND METHODS

Isolated cases of lower abdomen cysts encountered in the first trimester at the Prenatal Diagnosis Unit during the last 5 years were retrieved and compared with those found in literature. Post-natal clinical data were analyzed to check the presence and type of malformations.

RESULTS

A total of three cases of lower abdomen cysts were found in our center and 13 in literature. In our case series all the cysts spontaneously regressed and were no longer visible since the second trimester of pregnancy, while in literature this was reported in only 4 out of 13 cases. ARM was confirmed in all patients at birth or post-mortem.

CONCLUSIONS

The finding of a lower abdomen cyst during the first trimester of pregnancy could be an early predictive sign of ARM, even if it disappears during pregnancy. In these cases, we suggest mentioning to the parents the possibility of an ARM during the counseling and to refer the couple to a Colorectal Center.

A Spectrum of Ultrasound and MR Imaging of Fetal Gastrointestinal Abnormalities: Part 2 Anorectal Malformation, Liver, and Abdominal Wall Anomalies

Ultrasound (US) and magnetic resonance imaging (MRI) are two modalities for diagnosing fetal gastrointestinal (GI) anomalies. Ultrasound (US) is the modality of choice. MRI can be used as a complementary method. Despite its expanding utilization in central nervous system (CNS) fetal malformation, MRI has not yet been established for evaluation of fetal GI abnormalities. Therefore, more attention should be paid to the clinical implications of MRI investigations following screening by US.

A Spectrum of Ultrasound and MR Imaging of Fetal Gastrointestinal Abnormalities: Part 1 Esophagus to Colon

Ultrasound (US) and magnetic resonance imaging (MRI) are two modalities for diagnosing fetal gastrointestinal (GI) anomalies. Ultrasound (US) is the modality of choice. MRI can be used as a complementary method. Despite its expanding utilization in central nervous system (CNS) fetal malformation, MRI has not yet been established for evaluation of fetal GI abnormalities. Therefore, more attention should be paid to the clinical implications of MRI investigations following screening by US.

Visualization of the fetal anus by prenatal ultrasound for the diagnosis of anorectal malformations: is it feasible?

PURPOSE

The goal of this study was to determine the feasibility of identifying the anal dimple (AD) on routine prenatal ultrasound. Using the presence, absence, appearance, and location of the anal dimple as an indirect sign for possible underlying anorectal malformations (ARM), we hypothesize that evaluation of the anal dimple as part of the fetal anatomic survey may increase the sensitivity in detecting less severe ARMs.

METHODS

In a prospective longitudinal observational study, pregnant women who underwent prenatal ultrasound (US) at the Colorado Fetal Care Center between January 2019 and 2020 were enrolled. The variables recorded included gestational age, singleton versus multiple pregnancy, gender of the fetus, visualization of the AD, and reason for non-visualization of the AD.

RESULTS

A total of 900 ultrasounds were performed, evaluating 1044 fetuses, in 372 different pregnant women. Gestational ages ranged from 16 to 38 weeks. The AD was visualized in 612 fetuses (58.6%) and not seen in 432 (41.4%). The two most common reasons for non-visualization were extremes in gestational age (n = 155; 36%) and fetal position (n = 152; 35.3%). The optimal gestational age range for AD visualization was 28-33 weeks + 6 days, with 78.1% visualization rate.

CONCLUSION

Visualization of the anal dimple by ultrasound is feasible and may aid in the detection of less severe ARMs, ultimately impacting pregnancy management and family counseling. The optimal timing for anal dimple visualization is late second and third trimester.

Prenatal imaging of anorectal malformations - 10-year experience at a tertiary center in Switzerland

BACKGROUND

Anorectal malformation is a spectrum of congenital defects of the distal bowel, mostly diagnosed at birth.

OBJECTIVE

To describe the prenatal imaging findings of anorectal malformations, explore the causes of the low rates of prenatal diagnosis, compare the accuracy of prenatal ultrasound (US) and magnetic resonnance imaging [MRI] and evaluate the relevance of information obtained at MRI.

MATERIALS AND METHODS

Children treated for anorectal malformation at our hospital and with available prenatal studies were retrospectively identified and included in the study. We reviewed prenatal imaging exams, listed findings suggestive of the diagnosis, and compared results with the final classification.

RESULTS

Fourteen fetuses and neonates - eight with intermediate-high type anorectal malformation and six with cloacae - fulfilled the inclusion criteria. All had associated congenital anomalies. Prenatal exams included 13 US and 8 MRI exams, with 7 children having both exams. Suggestive findings for anorectal malformation were detected in 50% of the cases prenatally and in 85% upon review. They were prospectively detected in 31% and 50% of the cases at US and MRI and retrospectively in 62% and 100% at US and MRI, respectively. MRI was superior to US because it improved the diagnosis, especially in cloacae, and provided relevant additional information that changed management in two cases.

CONCLUSION

The most important signs suggesting anorectal malformation are an absent target sign and anomalous distal bowel wall and rectal fluid. Complementary prenatal MRI improves the diagnosis of anorectal malformation.

Fetal megacystis: a lot more than LUTO

OBJECTIVE

Fetal megacystis presents a challenge in terms of counseling and management because of its varied etiology and evolution. The aim of this study was to present a comprehensive overview of the underlying etiologies and structural anomalies associated with fetal megacystis.

METHODS

This was a retrospective multicenter study of cases referred to the fetal medicine unit of one of the eight academic hospitals in The Netherlands with a diagnosis of fetal megacystis. For each case, data on and measurements of fetal urinary tract and associated structural anomalies were collected. All available postmortem examinations and postnatal investigations were reviewed in order to establish the final diagnosis. In the first trimester, fetal megacystis was defined as longitudinal bladder diameter (LBD) ≥ 7 mm, and in the second and third trimesters as an enlarged bladder failing to empty during an extended ultrasound examination lasting at least 40 min.

RESULTS

Of the 541 pregnancies with fetal megacystis, it was isolated (or solely accompanied by other signs of lower urinary tract obstruction (LUTO)) in 360 (67%) cases and associated with other abnormal ultrasound findings in 181 (33%) cases. The most common associated ultrasound anomaly was an increased nuchal translucency thickness (22%), followed by single umbilical artery (10%) and cardiac defect (10%). A final diagnosis was established in 418 cases, including 222 (53%) cases with isolated LUTO and 60 (14%) infants with normal micturition or minor isolated urological anomalies. In the remaining 136 (33%) cases, concomitant developmental or chromosomal abnormality or genetic syndrome was diagnosed. Overall, 40 chromosomal abnormalities were diagnosed, including trisomy 18 (n = 24), trisomy 21 (n = 5), Turner syndrome (n = 5), trisomy 13 (n = 3) and 22q11 deletion (n = 3). Thirty-two cases presented with anorectal malformations involving the anus, rectum and urogenital tract. In cases with confirmed urethral and anal atresia, megacystis occurred early in pregnancy and the bladder appeared severely distended (the LBD (in mm) was equal to or greater than twice the gestational age (in weeks)). Fetal macrosomia was detected in six cases and an overgrowth syndrome was detected in four cases, comprising two infants with Beckwith-Wiedemann syndrome and two with Sotos syndrome. Megacystis-microcolon-intestinal hypoperistalsis syndrome was diagnosed in five (1%) cases and prenatally suspected only in one case.

CONCLUSIONS

Although the main cause of fetal megacystis is LUTO, an enlarged fetal bladder can also be present as a concomitant finding of miscellaneous genetic syndromes, developmental disturbances and chromosomal abnormalities. We provide an overview of the structural anomalies and congenital disorders associated with fetal megacystis and propose a practical guide for the differential diagnosis of genetic syndromes and chromosomal and developmental abnormalities in pregnancies presenting with fetal megacystis, focusing on the morphological examination of the fetus. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Prenatal Evaluation for Detection of Anorectal Atresia: Value of Ultrasound

OBJECTIVES

To investigate the applicability and value of ultrasound (US) in the diagnosis of anorectal atresia.

METHODS

Between January 2008 and January 2016, we prospectively evaluated 63,101 fetuses (gestational age, 20-38 weeks), including low- and high-risk populations using 2-dimensional US scans. An abnormal imaging finding was defined as an anal canal diameter of less than the 95% confidence interval (small anal canal) of the normal range or the absence of an anal canal and rectum. Imaging findings were considered normal on detection of an anal canal with a normal width and the absence of abnormalities. Prenatal imaging findings were confirmed by a postnatal or postmortem examination.

RESULTS

Among the investigated fetuses, 28 showed evidence of anorectal atresia on US scans, and 22 of those with anorectal atresia had additional anomalies. Six cases of isolated anorectal atresia were successfully detected during the preclusive prenatal US scans. Four cases of a low imperforate anus (including 2 covered anuses) yielded false-negative results, indicating a diagnostic rate of 87.5% (28 of 32). The normal appearance of the fetal rectum and anal canal ruled out anorectal atresia in 30 fetuses with a dilated colon. Additionally, there were 3 false-positive cases, in which a narrow anal canal was observed.

CONCLUSIONS

Identifying the abnormal appearance or absence of the fetal anal canal and rectum on preclusive US anomaly scans is useful for prenatal diagnosis or exclusion of anorectal atresia, which may help improve the detection of isolated anorectal atresia. Furthermore, a combined evaluation of the longitudinal and axial appearances of the fetal anal canal and rectum can improve diagnostic accuracy.

The spectrum of cloacal malformations: how to differentiate each entity prenatally with fetal MRI

The term cloacal malformation is commonly used to describe the classic cloacal malformation where there is a single common urogenital and intestinal channel located at the expected site of the urethra. There is, however, a spectrum of cloacal abnormalities that differ from this classic type and are less well discussed in the radiologic and surgical literature. The aim of this pictorial essay is to familiarize radiologists with the anatomy, appropriate terminology and key prenatal imaging findings that differentiate the six entities that constitute the spectrum of cloacal abnormalities.

Differences in Origin and Outcome of Intra-Abdominal Cysts in Male and Female Fetuses

OBJECTIVE

To investigate the origin and outcome in a cohort of male and female fetuses with intra-abdominal cysts, in order to provide recommendations on management and to improve prenatal counselling.

METHODS

From 2002 to 2016, intra-abdominal cysts were detected by ultrasound in 158 fetuses. Cases with an umbilical vein varix were excluded. Fetal, neonatal, and maternal characteristics were retrieved from electronic patient files.

RESULTS

In female fetuses (n = 114), intra-abdominal cysts were diagnosed at a later gestational age compared with male fetuses (n = 44) (median 32.0 vs. 21.5 weeks, p < 0.001). The maximum prenatal cyst diameter was larger in female fetuses (median 35 vs. 17 mm, p < 0.001). Associated anomalies were less frequent in females (n = 15, 13.2%) compared with males (n = 15, 34.1%). In females (n = 114), most cysts were of ovarian origin (n = 81, 71.1%). Surgery was performed in 30 (26.3%) female and 15 (34.1%) male neonates (p = 0.33). Anorectal malformations were present in 6 cases and often not recognized prenatally.

CONCLUSIONS

The differences in the origin of intra-abdominal cysts between male and female fetuses, resulting in differences in prenatal presentation and postnatal outcome should be taken into account in prenatal counseling within a multidisciplinary team. Evaluation of the fetal perianal muscular complex is indicated.

First trimester expression of anorectal malformation: Case report and review of the literature

A 26-years-old woman, underwent an ultrasound examination at 13.4 weeks. A cystic structure was identified in the right lower abdomen. Gradually, the cystic mass was replaced by echogenic content and eventually attained the appearance of hyperechoic bowel. At 21.2 weeks, the anal sphincter could not be demonstrated which was consistent with the diagnosis of isolated anal agenesis. Amniocentesis revealed 46XY karyotype with normal comparative genomic hybridization. After termination of pregnancy at 23 weeks, an autopsy revealed an isolated high type anorectal malformation (ARM) without fistula. We reviewed all 14 cases reported in the literature of first trimester sonographic expression of ARM.

Giant fetal hydrometrocolpos associated with cloacal anomaly causing postnatal respiratory distress

Persistent cloaca is a rare presentation wherein the urethra, vagina, and rectum converge into a common channel with a single perineal opening. Fetal hydrometrocolpos can result if fluid accumulates behind an obstruction of this common channel. A 29-year-old woman (G4P1021) was referred at 36 2/7 weeks of gestation for evaluation of a fetal abdominal cystic mass. Detailed ultrasonography and magnetic resonance imaging showed two symmetric cystic masses, bilateral hydronephrosis, and oligohydramnios. Elective cesarean delivery was performed at 37 0/7 weeks; the baby weighed 4043 g with Apgar scores of 5 and 6 at 1 and 5 min. Intubation was performed for respiratory distress, and the infant was noted to have an imperforate anus; persistent cloaca was diagnosed. Drainage of the hydrometrocolpos improved the infant's breathing remarkably, and extubation was achieved. This child's imaging findings are among the largest ever reported, and resulted in neonatal respiratory distress.

[Fetal abdominal cysts at the first trimester scan]

OBJECTIVES

Abdominal cysts are seldom detected at the first trimester scan. The aim of this study is to ascertain their outcome, which is currently not established.

METHODS

The French College of Fetal Ultrasound conducted a prospective observational study of 24months, collecting all cases of abdominal cysts discovered during the first trimester ultrasound. Cases of megacystis were excluded from the study. Ultrasound images, prenatal diagnosis expert reports and pregnancy outcomes were collected by sonographers after patient consent.

RESULTS

Ten cases of abdominal cysts were collected. The cysts had a mean diameter of 15mm. They were anechoic in 5 cases, hyperechoic in 2 cases and mixed in 3 cases. In 6 of 10 cases, complete resolution was observed at 18WG with a good post-natal outcome; the five cases with anechoic images were associated with normal pediatric examination at birth and in the case of the resolved hyperechoic image, an isolated imperforate anus was observed. In the four cases of hyperechoic or mixed images that had not resolved, the outcome was poor with four termination of pregnancies, including two cases of cloacal dysgenesis.

CONCLUSIONS

Abdominal cysts are rare at the first trimester scan. They resolve in two thirds of cases and are then associated with good outcome. When they do not resolve or when they are not strictly anechoic, they require a referral ultrasound examination at 18 and 22WG.

Sonographic Determination of Type in a Fetal Imperforate Anus

OBJECTIVES

The purpose of this study was to determine the type of an imperforate anus by using sonography in the prenatal period.

METHODS

This retrospective study evaluated the fetal anus in all pregnant women, including low- and high-risk populations, between February 2010 and November 2013. High-type imperforate anuses were diagnosed by prenatal sonography when the anal sphincter muscles and anal canal mucosa were not visible. Low-type imperforate anuses were prenatally suspected when at least 1 of the following was present: (1) a small anus; (2) no visible anal mucosa; or (3) close location of the genitalia by the anus without a visible perineal body, particularly in a female fetus.

RESULTS

Among the 9499 fetuses, 41 were prenatally suspected of having an imperforate anus, and 32 were confirmed to have this disorder. During the same study period, there were 11 false-negative cases, for a diagnostic sensitivity rate of 74%. All 9 fetuses who were confirmed to have a normal anus were prenatally suspected of having a low-type imperforate anus. Among the 32 fetuses with a confirmed imperforate anus, 19 were confirmed to have a high or intermediate type and 13 to have a low type. The type in 3 fetuses was incorrectly determined prenatally.

CONCLUSIONS

Although an imperforate anus is not always diagnosed prenatally, its type can be determined by prenatal sonography.

Prenatal Imaging of the Gastrointestinal Tract with Postnatal Imaging Correlation

Prenatal detection of a wide variety of anomalies and masses of the gastrointestinal tract is now possible. Prenatal imaging with ultrasonography and in selected cases magnetic resonance imaging provides invaluable information to the referring obstetrician, the maternal fetal medicine specialist, the neonatologist and pediatrician who will care for the child after birth, the surgeons and pediatric specialists who will repair or manage a prenatally detected anomaly, and of course to the parents, allowing them to prepare psychologically and financially for the specific interventions that may be needed for their child. Additional screening for associated anomalies can take place, route of delivery can be decided, and arrangements for delivery in an appropriate setting can be made. Prenatal detection also allows for consideration for pregnancy termination. This article will give a broad overview of anomalies of the gastrointestinal tract that can be detected prenatally and their imaging appearance postnatally.

Evaluation of the perianal muscular complex in the prenatal diagnosis of anorectal atresia in a high-risk population

OBJECTIVES

To investigate whether sonographic identification of the fetal perianal muscular complex (PAMC) is of value in the prenatal detection of anorectal atresia in a high-risk population.

METHODS

During an 8-year study period, a total of 189 pregnancies at high risk for fetal anorectal atresia were prospectively examined for the presence/absence of the PAMC on axial ultrasound views of the fetal perineum. The prenatal findings were confirmed postnatally or at the time of postmortem examination.

RESULTS

The median gestational age at examination was 27 (range, 15-37) weeks. The PAMC was identified in 175 fetuses, all of which had a normal anorectal canal at the time of delivery or at postmortem examination. The PAMC was not identified prenatally in the 14 remaining cases, and the anus was absent in 11 fetuses with anorectal atresia and in two with urorectal septum malformation sequence. There was one false-positive case, in which the anus was anatomically and functionally normal but ectopically located, opening into the vaginal vestibule. Among these 14 cases of anorectal malformation, prenatal dilatation of the distal bowel was seen in nine (64.3%) and intraluminal calcified meconium or enterolithiasis in five (35.7%). Overall, absent PAMC on prenatal sonography in this high-risk population had a sensitivity of 100%, specificity of 99%, true-positive rate of 93% and false-positive rate of 7% for the diagnosis of anorectal atresia.

CONCLUSIONS

In a high-risk population, the absence of PAMC seems to be a highly sensitive and specific sonographic marker for anorectal atresia. The role of routine sonographic identification of the PAMC at the second-trimester scan to screen for cases of isolated anal atresia remains to be determined.

Sonographic depiction of the fetal anus and its utility in the diagnosis of anorectal malformations

OBJECTIVES

The purpose of this study was to describe the sonographic appearance of the fetal anus and its usefulness in diagnosis of anal atresia.

METHODS

An anomaly scan was performed in 13,150 patients over 8 years. Gestational ages ranged from 16 to 38 weeks. A tangential scan of the fetal perineum was performed. The anus was seen as a hypoechoic ring representing the wall of the anal canal with a central echogenic dot representing the lumen. This appearance was seen posterior to the external genitalia. If there was failure to see this appearance, a coronal scan of the fetal pelvis was done to look for the anal canal in contiguity with the rectum and to confirm its extension up to perineum. Failure to see these two features was considered diagnostic of anal atresia.

RESULTS

On the basis of these criteria, anal atresia was diagnosed in 17 fetuses. Sixteen of these fetuses also had other associated anomalies. The appearance of the anus was useful for ruling out anal atresia in 2 fetuses with a dilated colon containing echogenic meconium balls.

CONCLUSIONS

The anus is visible on a tangential scan of the fetal perineum. It can be seen routinely during an anomaly scan to diagnose or rule out anal atresia.