A relative shift in cloacal location repositions external genitalia in amniote evolution

The move of vertebrates to a terrestrial lifestyle required major adaptations in their locomotory apparatus and reproductive organs. While the fin-to-limb transition has received considerable attention, little is known about the developmental and evolutionary origins of external genitalia. Similarities in gene expression have been interpreted as a potential evolutionary link between the limb and genitals; however, no underlying developmental mechanism has been identified. We re-examined this question using micro-computed tomography, lineage tracing in three amniote clades, and RNA-sequencing-based transcriptional profiling. Here we show that the developmental origin of external genitalia has shifted through evolution, and in some taxa limbs and genitals share a common primordium. In squamates, the genitalia develop directly from the budding hindlimbs, or the remnants thereof, whereas in mice the genital tubercle originates from the ventral and tail bud mesenchyme. The recruitment of different cell populations for genital outgrowth follows a change in the relative position of the cloaca, the genitalia organizing centre. Ectopic grafting of the cloaca demonstrates the conserved ability of different mesenchymal cells to respond to these genitalia-inducing signals. Our results support a limb-like developmental origin of external genitalia as the ancestral condition. Moreover, they suggest that a change in the relative position of the cloacal signalling centre during evolution has led to an altered developmental route for external genitalia in mammals, while preserving parts of the ancestral limb molecular circuitry owing to a common evolutionary origin.

Embryonic origin and remodeling of the urinary and digestive outlets

Separating digestive and urinary outlets is a critical step during mammalian embryogenesis. However, the natural history of these structures is poorly studied, and little is known about their embryonic origin. Here, we show that peri-cloacal mesenchymal (PCM) progenitors are the major source of these structures. Surprisingly, PCM progenitors also contribute to perineum, a structural barrier separating the urinary and digestive tracts, suggesting a potential role of PCM progenitors in establishing independent urinary and digestive outlets. We demonstrate that Six1 and Six2 are complementarily but asymmetrically expressed in the PCM progenitors. Deletion of these genes results in decreased cell survival and proliferation, and consequently in agenesis of the perineum and severe hypoplasia of the genital tubercle. Together, these findings suggest that PCM progenitors are the unexpected source of perineum and genital tubercle, and establish a basic framework for investigating normal and abnormal development of anorectal and genitourinary structures.

Cloacal malformation: embryology, anatomy, and prenatal imaging features

Cloacal malformation is a rare but important anomaly. Prenatal diagnosis is possible with knowledge of the distinctive imaging features. The purpose of this case series is to illustrate characteristic prenatal sonographic and magnetic resonance imaging features of cloacal malformation using imaging from 6 cases seen at a single academic center to augment published data. The imaging feature common to all cases was a central cystic pelvic mass containing a characteristic fluid-fluid level. Additional anomalies include uterine and vaginal duplication, hydronephrosis, and lumbosacral anomalies. Prenatal magnetic resonance imaging showed the absence of the normal T1-hyperintense meconium-filled rectum in all cases. Prenatal diagnosis may affect immediate neonatal care (eg, immediate drainage of hydrocolpos) with an ultimate improved outcome.

Antenatal diagnosis of bladder/cloacal exstrophy: challenges and possible solutions

OBJECTIVE

To identify the pitfalls in accurate antenatal diagnosis of bladder exstrophy (BE) and cloacal exstrophy (CE), and thus understand the challenges for antenatal counselling.

METHODS

A prospectively maintained bladder exstrophy database of antenatal and live born referrals for BE/CE was used to identify patients. Data were collected about the antenatal scan findings and the outcome of pregnancy.

RESULTS

Between 2003 and 2009, 40 new babies with BE/CE were referred and of them 10 had an antenatal diagnosis. Five patients did not have a diagnosis despite suspicious findings noted on antenatal scans and another three had a wrong diagnosis of BE/CE. Of the 16 referrals with antenatal suspicion of BE/CE, 5 opted for termination. At the 20-week scan, it was possible to identify the gender of the fetus in 3/16 cases only.

CONCLUSIONS

Only a quarter of the babies born with BE/CE had received an antenatal diagnosis. Raising awareness about the condition amongst radiographers, and facilitating further scanning by a specialist fetal management unit if suspicious findings are noted, is crucial for improving the rate of detection. An antenatal diagnosis may not be reliable, and difficulty in identifying gender at the 20-week scan adds to the complexity of antenatal counselling. Magnetic resonance imaging and karyotyping may provide additional helpful information.

Bmp7 functions via a polarity mechanism to promote cloacal septation

BACKGROUND

During normal development in human and other placental mammals, the embryonic cloacal cavity separates along the axial longitudinal plane to give rise to the urethral system, ventrally, and the rectum, dorsally. Defects in cloacal development are very common and present clinically as a rectourethral fistula in about 1 in 5,000 live human births. Yet, the cellular mechanisms of cloacal septation remain poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

We previously detected Bone morphogenetic protein 7 (Bmp7) expression in the urorectal mesenchyme (URM), and have shown that loss of Bmp7 function results in the arrest of cloacal septation. Here, we present evidence that cloacal partitioning is driven by Bmp7 signaling in the cloacal endoderm. We performed TUNEL and immunofluorescent analysis on cloacal sections from Bmp7 null and control littermate embryos. We found that loss of Bmp7 results in a dramatic decrease in the endoderm survival and a delay in differentiation. We used immunological methods to show that Bmp7 functions by activating the c-Jun N-terminal kinase (JNK) pathway. We carried out confocal and 3D imaging analysis of mitotic chromosome bundles to show that during normal septation cells in the cloacal endoderm divide predominantly in the apical-basal direction. Loss of Bmp7/JNK signaling results in randomization of mitotic angles in the cloacal endoderm. We also conducted immunohistochemical analysis of human fetal sections to show that BMP/phospho-SMAD and JNK pathways function in the human cloacal region similar as in the mouse.

CONCLUSION/SIGNIFICANCE

Our results strongly indicate that Bmp7/JNK signaling regulates remodeling of the cloacal endoderm resulting in a topological separation of the urinary and digestive systems. Our study points to the importance of Bmp and JNK signaling in cloacal development and rectourethral malformations.

Long-term survival with cloacal dysgenesis sequence

Cloacal dysgenesis sequence (CDS) is a rare and lethal malformation. We report such a case of long-term survival, currently to 12 years of age. In the fetal period, she received a timely placement of vesico-amniotic shunt for a megabladder due to a severe urethral obstruction. Postnatally, cystostomy and colostomy were created because of no perineal opening of urethra, vagina, and anus. Anorectoplasty, construction of efferent conduit, and colostomy closure were performed at 4 years of age. Ileovaginoplasty and ileovesicostomy which was a Mitrofanoff-type of conduit, and labioplasty were performed at the age of 11 years. To the best of our knowledge, only five survivors with CDS over 1 year of age have been reported.

Long-term survival and renal transplantation in a monozygotic twin with cloacal dysgenesis sequence

Cloacal dysgenesis sequence (CDS) is a severe hindgut malformation occurring in 1:50,000 to 250,000 live births (Qureshi et al. Prenatal diagnosis of cloacal dysgenesis sequence: differential diagnosis from other forms of fetal obstructive uropathy. Fetal Diagn Ther 1998;13:69-74; Bargaje et al. Cloacal dysgenesis sequence. Ann Diagn Pathol 2008;12:62-66). It is characterized by a smooth perineum with no urethral, vaginal, or anal openings, and lack of labioscrotal development. Typically, the bladder, vagina, and colon each end blindly, although persistent cloaca without perineal orifice can be seen. With no egress for urine, infants have renal insufficiency and pulmonary hypoplasia, usually making CDS lethal (Sahinoglu Z et al. The prenatal diagnosis of cloacal dysgenesis in six cases: can the termination of pregnancy always be the first choice? Prenat Diagn 2004;24:10-16). Reported survivors have had a persistent urachus or have been spared the effects of oligohydramnios by the presence of a twin (Liang X. Cloacal dysgenesis sequence: observations in four patients, including three fetuses of second trimester gestation. Pediatr Dev Pathol 1998;1:281-288). We report a case of long-term survival, currently to 25 months of age, and renal transplantation in a monochorionic, diamniotic twin girl with CDS.

Cell apoptosis during the cloacal embryonic development in rats with anorectal malformations

OBJECTIVE

In the normal embryonic development of anorectum, apoptosis plays an important role. To explore the role of apoptosis in anorectal malformations (ARM), this study investigated cell apoptosis during the cloacal embryonic development in ARM embryos.

METHODS

ARM embryos were induced by intragastric administration of ethylenethiourea (125 mg/kg) for pregnant rats on embryonic day 10 (E10). The distribution of apoptotic cells in the cloaca was ascertained by hematoxylin and eosin and TUNEL staining in the normal control embryos (n=102) and ARM embryos (n=147) on E13, E13.5, E14, E15 and E16.

RESULTS

On E13, apoptotic cells were detected in the urorectal septum of rat embryos in the control group. With the development of embryos, the number of apoptotic cells in the mesenchyme of urorectal septum gradually increased and a large number of apoptotic cells were seen in the dorsal rectal mesenchyme. On E14, apoptotic cells appeared at the terminal rectum and the dorsal cloacal membrane. On E15, the urorectal septum fused with the cloacal membrane and apoptotic cells in the urorectal septum mesenchyme continuously extended down to the fusion region. Compared with the control group, apoptotic cells in the urorectal septum, the dorsal rectal mesenchyme and the cloacal membrane of the ARM rat embryos were significantly reduced during the embryonic development. The development of the urorectal septum was delayed and it did not fuse with the cloacal membrane in ARM embryos.

CONCLUSIONS

During the embryonic development of cloaca, abnormal apoptosis in the urorectal septum, the dorsal rectal mesenchyme and the cloacal membrane may be one of the reasons for anorectal malformations. The proper regulation of cell apoptosis may be one of the key mechanisms for normal development of anorectum in the embryonic stage.

RET/GDNF signalling in vagal neural crest-derived neurons of the chick embryo cloaca

INTRODUCTION

The growth factor, 'Glial cell line-Derived Neurotrophic Factor' (GDNF), is involved in the development of enteric ganglia, using the tyrosine kinase receptor 'REarranged during Transfection' (RET) to stimulate the proliferation and differentiation of neural crest-derived precursor cells. To date, the presence of these signalling molecules have not been studied in the developing cloaca, thus the aim of this study was to investigate the distribution of RET and GDNF, and analyse their co-localisation in vagal-derived neurons of the cloaca using quail-chick chimera embryos.

MATERIALS AND METHODS

Chicken embryos were incubated until the 10-12 somite stage. The vagal neural tube was microsurgically ablated in ovo and replaced with the vagal neural tube from age-matched quail embryos. Quail-chick chimera embryos were harvested at E12, fixed and embedded in paraffin wax, and serially sectioned. Immunohistochemistry was performed using human natural killer-1 (HNK-1), quail-cell-specific perinuclear (QCPN), GDNF and RET antibodies.

RESULTS

HNK-1 labelled all ganglia in the myenteric and submucosal plexuses of the cloaca, while the quail-specific QCPN antibody labelled all ganglia derived from the transplanted quail vagal neural tube (Fig. 1, a, b). RET and GDNF were found both co-localised and expressed in separate ganglia in the cloaca (Fig. 1, c, d). The majority of QCPN-labelled vagal-derived neurons also expressed RET and GDNF. Fig. 1 HNK-1 (a), QCPN (b), GDNF (c) and RET (d) immunoreactivity in the chick cloaca at E12. Arrows show ganglia displaying co-immunoreactivity for all four antibodies

CONCLUSION

Results show that GDNF and RET signalling play a major role in ENS development in the chick embryo cloaca. We have shown, for the first time, that the majority of vagal neural crest-derived neurons co-express RET and GDNF, thus highlighting the importance of these signalling factors in cloacal development.

Cloacal exstrophy: a case study

Cloacal exstrophy is a complex congenital anomaly that affects both the gastrointestinal and genitourinary systems. It is characterized by an omphalocele, an exstrophied bladder, abnormal genitalia, and imperforate anus. Prior to 1960, there were no reported cases of survival, but because of advancements in neonatology, surgery, and anesthesiology, the survival rate has improved drastically. This case presentation of an infant born with cloacal exstrophy includes discussion of etiology, diagnosis, treatment, ethical issues, and nursing care.

The role of Shh transcription activator Gli2 in chick cloacal development

Patterning and differentiation along the dorsal-ventral (D-V) axis lead to cloacal partitioning into ventral urinary and dorsal alimentary tracts in most mammals, but not birds and fish. We previously reported that the major activator of Sonic hedgehog (Shh) signaling transcription factor Gli2 plays an essential role in cloacal partitioning along the D-V axis in a mouse model. Here, we report that chick cloacal patterning and differentiation is along the anterior-posterior axis. During chick cloacal formation, Shh is expressed strongly in hindgut endoderm; Gli2 is very weakly detected in the surrounding hindgut mesoderm. In the mesoderm of the cloacal region, the over-expression of the constitutively active form of mouse Gli2 has been shown to: not induce cloacal partitioning along the D-V axis; induce expression of Ptch1, Gli2, bmp4, wnt5a, and hoxd-13, which have been previously shown to play a role in hindgut patterning; increase cell proliferation; and reduce apoptosis. Interestingly, p63 expression in the cloacal endoderm is also up-regulated, suggesting an interaction between the Shh and p63 pathways. In conclusion, Gli2 alone is insufficient to induce partitioning along the D-V axis in the chick embryo. However, Gli2 regulates both epithelial and mesenchymal cell proliferation and apoptosis during cloacal development.

Staging of intestinal development in the chick embryo

Comparisons between developmental studies rely on embryonic staging systems. It is important for comparison of molecular, immunohistochemical, and physiological studies of the developing chick intestine that the developmental stage of embryos is reliably determined. Good staging systems exist for the external features of the chick embryo but not for development of internal organs. To facilitate precise comparisons of chick embryo intestine development, we prepared an intestinal staging system. Embryos were fixed, other tissues dissected away, and the intestine and associated organs were then drawn to scale using a camera lucida. This produced black-and-white drawings with features of the gut clearly visible. The detailed drawings of intestine from chick embryos aged 2.5 to 10 days were correlated with age of embryos and developmental stages described in three common staging systems, Hamilton and Hamburger, Thompson and Fitzharris, and Allan and Newgreen. Descriptions of key changes in gut morphology and position are given for each stage. This staging of chick gut development will allow future studies to quote and compare development of the gut rather than external features or incubation time. This will allow much more precise reporting and comparisons in developmental studies of cell migration and gene expression.

Sustained Bmp signaling is essential for cloaca development in zebrafish

Bone morphogenetic protein (Bmp) signaling has long been known to be important for the early development of the ventral mesoderm, including blood,vasculature and kidney cells. Although Bmp genes are continually expressed in the ventral cells throughout gastrulation and somitogenesis, previous studies in zebrafish have not addressed how the role of Bmp signaling changes over time to regulate ventral mesoderm development. Here, we describe the use of a transgenic inducible dominant-negative Bmp receptor line to examine the temporal roles of Bmp signaling in ventral mesoderm patterning. Surprisingly,we find that Bmp signaling from the mid-gastrula stage through early somitogenesis is important for excluding blood and vascular precursors from the extreme ventral mesoderm, and we show that this domain is normally required for development of the cloaca (the common gut and urogenital opening). Using a novel assay for cloacal function, we find that larvae with reduced mid-gastrula Bmp signaling cannot properly excrete waste. We show that the cloacal defects result from alterations in the morphogenesis of the cloaca and from changes in the expression of genes marking the excretory system. Finally, we show that HrT, a T-box transcription factor, is a Bmp-regulated gene that has an essential function in cloacal development. We conclude that sustained Bmp signaling plays an important role in specification of the zebrafish cloaca by maintaining the fate of extreme ventral cells during the course of gastrulation and early somitogenesis. Furthermore, our data suggest that alterations in Bmp signaling are one possible cause of anorectal malformations during human embryogenesis.

Morphology of the enteric nervous system in the hindgut of an infant with cloacal exstrophy

The authors describe the morphology of the enteric nervous system in the hindgut of an infant with cloacal exstrophy. Cloacal exstrophy was diagnosed at 32 weeks' gestation using prenatal ultrasonography. The baby was delivered at 34 weeks' gestation and underwent a separation of the cecum from bladder halves, reapproximation of hemibladders, closure of the omphalocele and pubic symphysis, and a distal colostomy. Intestinal wall specimens were obtained at colostomy from the distal end of the rudimentary hindgut. Serial frozen sections were prepared for histochemical acetylcholinesterase staining. Histological investigations demonstrated a strikingly crowded, immature enteric ganglia and prominent bundles of wandering cholinergic nerves. These findings suggest the unique pathology of the enteric nervous system development in cloacal exstrophy, in which the rudimentary hindgut behaves as a blind alley of the migratory pathway for neural crest-derived cells during embryogenesis. Histological examinations of the hindgut enteric nervous system in cloacal exstrophy may be beneficial for evaluating the postnatal development of the distal colon which might be utilized for a pull-through procedure.

Cellular proliferation in the urorectal septation complex of the human embryo at Carnegie stages 13-18: a nuclear area-based morphometric analysis

In order to analyse the patterns of cellular proliferation both in the mesenchyme of the urorectal septum (URS) and in the adjacent territories (posterior urogenital mesenchyme, anterior intestinal mesenchyme and cloacal folds mesenchyme), as well as their contribution to the process of cloacal division, a computer-assisted method was used to obtain the nuclear area of 3874 mesenchymal cells from camera lucida drawings of nuclear contours of selected sections of human embryos [Carnegie stages (CSs) 13-18]. Based on changes in the size of the nucleus during the cellular cycle, we considered proliferating cells in each territory to be those with a nuclear area over the 75th percentile. The URS showed increasing cell proliferation, with proliferation patterns that coincided closely with cloacal folds mesenchyme, and with less overall proliferation than urogenital and intestinal mesenchymes. Furthermore, at CS 18, we observed the beginning of the rupture in the cloacal membrane; however, no fusion has been demonstrated either between the URS and the cloacal membrane or between the cloacal folds. The results suggest that cloacal division depends on a morphogenetic complex where the URS adjacent territories could determine septal displacement at the time that their mesenchymes could be partially incorporated within the proliferating URS.

Sonic hedgehog expression in the development of hindgut in ETU-exposed fetal rats

Sonic hedgehog (Shh) has been shown to be involved in the morphogenesis of many organ systems including the notochord, floor plate and limbs, as well as in the development of the left-right axis in vertebrates. Recent evidence suggests the Shh cascade plays a crucial role in the development of the foregut and hindgut. We have previously shown that prenatal exposure of fetal rats to ethylenethiourea (ETU) induces hindgut malformations and other abnormalities of the VACTERL association. The aim of this study was to determine the pattern of expression of Shh and its downstream genes during hindgut development in ETU-exposed embryos with anorectal malformations (ARMs). Pregnant Sprague-Dawley rats were mated together overnight and a positive vaginal plug was marked as gD0. On gD10, 1% ETU (125 mg/kg) was given to the experimental group and controls received the same volume of saline. Embryos were collected from both groups at gD12-16. The developing hindgut of each embryo was dissected under magnification and snap frozen. Highly purified RNA was isolated from each hindgut and first strand cDNA was prepared with appropriate negative controls. Reverse transcriptase (RT) polymerase chain reaction (PCR) was done to determine the transcripts of Shh in each sample and quantitative real-time PCR was carried out to show relative quantitative expression of Shh at each time point. Shh was detected in all samples confirming that Shh is active during the process of hindgut development in fetal rats. Relative quantitation demonstrated that Shh expression shows time-dependent changes in the developing hindgut of ETU-exposed rat embryos, and when results were compared with control samples, there was significant decrease in expression on gD14 and 15, when the cloaca normally separates into the rectum and urethra occurs in the rat fetus. The misregulated expression of Shh in the hindgut of ETU-exposed rat embryos suggests that ETU may interfere with Shh signalling. Downregulation at the time of cloacal separation into rectum and urethra indicates that Shh plays a crucial role in the development of hindgut.

Differences in nitrergic innervation of the developing chick cloaca and colorectum

The intrinsic innervation of the developing gut has long been a subject of investigation, but little is known regarding that of the embryonic cloaca. The cloaca, like the rest of the gastrointestinal tract, is intrinsically innervated by the enteric nervous system. Nitrergic neurons and fibres make up a large part of this system, thus, their distribution provides us with a useful insight into its development. Cloacal and colorectal tissue specimens were removed from chick embryos at embryonic days 11 (E11), E15 and E19. NADPH-diaphorase (NADPH-d) histochemistry was carried out using whole mount tissue preparations. Ganglia density, the number of NADPH-d-positive cells per ganglia in the myenteric plexus and cell size were calculated and statistical analysis was performed to compare both regions of the gut (P<0.001). There were significant differences in the ganglia density in the cloaca compared to the colorectum at E11 (P<0.05) and E15 (P<0.01), with the colorectum having a much denser network. In both the cloaca and the colorectum, ganglia density significantly decreased with age (P<0.001), while significant differences were observed in the number of NADPH-d-positive cells per ganglia in both regions through development. Total cell size was similar in both the cloaca and colorectum at each stage and increased in both regions through development, predominantly due to an increase in the cytoplasm. Results reveal striking differences in innervation between the chick embryo cloaca and colorectum. The sparse network of innervation evident within the cloaca in contrast to the dense network within the colorectum emphasizes the individuality of both regions. These results highlight the need for a further in-depth analysis of the enteric nervous system's development within the embryonic cloaca.

Association of cloacal anomalies, caudal duplication, and twinning

Cloacal anomalies exhibit a wide variety of morphologic types and accompanying clinical severity. The association of malformations of the cloaca with partial, complete, or conjoined twinning has been appreciated for some time, but, with the advent of prenatal ultrasound technology, appears to occur with a greater frequency than once thought. This observation has important implications for pathogenesis. We present 2 representative cases, a 19-week-old female fetus with duplication of several caudal structures and a 21-week-old male fetus with cloacal exstrophy variant and demised co-twin with lower abdominal wall defect, extruded intestinal tract, absent external genitalia, and imperforate anus. These findings and previously published theories suggest that certain models of monozygotic twinning may apply to the pathogenesis of cloacal anomalies. Specifically, the partial or complete duplication of the organizing center within a single embryonic disc may increase the risk of mesodermal insufficiency and thus account for the failure of complete development of the cloacal membrane and consequent exstrophy or other aberration.

The effect of vagal neural crest ablation on the chick embryo cloaca

The cloaca, the caudal limit of the avian gastrointestinal tract, acts as a collecting chamber into which the gastrointestinal, urinary, and genital tracts discharge. It is intrinsically innervated by the enteric nervous system, which is derived from neural crest emigres that migrate from the vagal and sacral regions of the neural tube. Abnormal cloacal development can cause a number of anorectal anomalies, including persistent cloaca. Ablation of the vagal neural crest has previously been shown to result in an aganglionic hindgut to the extent of the colorectum. The aim of our study was to investigate the effect of vagal neural crest ablation on the cloaca, the limit of the hindgut in the developing chick embryo. Chick embryos were incubated until the 10-12 somite stage. The vagal neural tube corresponding to the level of somites 3-6 was then ablated, and eggs were incubated until harvested on embryonic day 11 (E11). Whole chick embryos were fixed, embedded in paraffin, and sectioned. Immunohistochemistry was then carried out using the HNK-1 monoclonal antibody to label neural crest cells, and results were assessed by light microscopy. Vagal neural crest ablation resulted in a dramatic decrease in the number of neural crest cells colonizing the chick embryo cloaca compared with control embryos. Ablated embryos contained only a small number of HNK-1-positive neural crest cells, which were scattered within the myenteric plexus in a disorganised pattern. Hypoganglionosis was also evident in other regions of the hindgut in ablated embryos. Ablation of the vagal neural crest results in a hypoganglionic cloaca in addition to hypoganglionosis of the hindgut. These results suggest that the cloaca is largely innervated by vagal neural crest emigres. Further studies involving quail-chick chimeras to investigate the exact contribution provided by both vagal and sacral neural crest cells to the cloaca should increase our understanding of the pathophysiology of conditions like persistent cloaca.

A dual fate of the hindlimb muscle mass: cloacal/perineal musculature develops from leg muscle cells

The cloaca serves as a common opening to the urinary and digestive systems. In most mammals, the cloaca is present only during embryogenesis, after which it undergoes a series of septation events leading to the formation of the anal canal and parts of the urogenital tract. During embryogenesis it is surrounded by skeletal muscle. The origin and the mechanisms regulating the development of these muscles have never been determined. Here, we show that the cloacal muscles of the chick originate from somites 30-34, which overlap the domain that gives rise to leg muscles (somites 26-33). Using molecular and cell labelling protocols, we have determined the aetiology of cloacal muscles. Surprisingly, we found that chick cloacal myoblasts first migrate into the developing leg bud and then extend out of the ventral muscle mass towards the cloacal tubercle. The development of homologous cloacal/perineal muscles was also examined in the mouse. Concordant with the results in birds, we found that perineal muscles in mammals also develop from the ventral muscle mass of the hindlimb. We provide genetic evidence that the perineal muscles are migratory, like limb muscles, by showing that they are absent in metd/d mutants. Using experimental embryological procedures (in chick) and genetic models (in chick and mouse), we show that the development of the cloacal musculature is dependent on proximal leg field formation. Thus, we have discovered a novel developmental mechanism in vertebrates whereby muscle cells first migrate from axially located somites to the pelvic limb, then extend towards the midline and only then differentiate into the single cloacal/perineal muscles.

Spatiotemporal distribution of apoptosis during normal cloacal development in mice

To understand normal cloacal developmental processes, serial sagittal sections of mouse embryos were made every 6 hrs from embryonic day 11.5 (E11.5) to E13.5. During cloacal development to form the urogenital sinus and anorectal canal, fusion of the urorectal septum with the cloacal membrane was not observed, and the ventral and dorsal parts of the cloaca were continuously connected by the canal until disappearance of the cloacal membrane to open the vestibule formed by the urogenital sinus and anorectal canal to the outside at E13.5. Ventral shifting of the dorsal part of the cloaca was observed until E12.5. The dorsal part was transformed in accordance with ventral shifting. In addition, apoptosis was seen to occur around the dorsal part. However, from E12.25, apoptotic cells are observed in a linear arrangement in the urorectal septum just ventral to the peritoneal cavity. Interestingly, extension of this line reaches the area of the cloacal membrane disintegrated by apoptosis. The present findings suggest that in the early stages (until E12.0), distribution of apoptosis in mesenchyme around the dorsal part of the cloaca might be strongly related to the transformation and ventral shifting of this part. Conversely, the apoptosis pattern in urorectal septum mesenchyme in later stages (from E12.0) might be involved in transformation of the urorectal septum and disintegration of the cloacal membrane.

The development of the male genitourinary system: II. The origin and formation of the urethral plate

The origin, extent and topographical relationships of the urethral plate and its role in the pathogenesis of developmental anomalies (bladder extrophy, epispadias and hypospadias) remain incompletely resolved. The commonly held view that the urethral plate (the forerunner of the urethra) arises through distal proliferation of the cells of the anterior wall of the cloaca cannot explain these anomalies. Given this and its newfound implications for hypospadias repair the development of the urethral plate is presented in detail. New insights into the origin of associated congenital defects are revealed.

The prenatal diagnosis of cloacal dysgenesis sequence in six cases: can the termination of pregnancy always be the first choice?

OBJECTIVE

Cloacal dysgenesis sequence is a lethal malformation, which usually requires termination. In this study, our aim was to evaluate the prenatal and postnatal diagnostic features of cloacal dysgenesis sequence and review the management of the patients.

MATERIAL AND METHODS

The data of six cases of cloacal dysgenesis sequences were collected from the ultrasonography and neonatal records. The findings were evaluated in prenatal and postnatal periods. Chromosomal analysis was performed in all the cases. The evaluation of primary and secondary malformations was done. Coexisting anomalies were searched for by radiology and histopathology.

RESULTS

Malformations in six cases (two females and four males) were described. The absence of anal, genital, and urinary openings with intact perineum covered by smooth skin were common findings. These features were considered as primary malformations for cloacal dysgenesis sequence. Secondary anomalies (urinary and gastrointestinal system malformations, pulmonary hypoplasia, and other coexisting anomalies) were evaluated.

CONCLUSION

The prenatal differential diagnosis of cloacal dysgenesis sequence from other urinary obstructive diseases was essential regarding fetal prognosis, prenatal, and neonatal management. The bladder outlet obstruction and pulmonary hypoplasia due to reduced amniotic fluid and/or kidney disease were considered prognostic factors for neonatal death. Termination of pregnancy is almost always recommended instead of intrauterine shunt procedures; but if we take into consideration one of our cases and a few reported cases who survived in the neonatal period, the prenatal management of these pregnancies needs to be reevaluated.

Normal and abnormal embryonic development of the anorectum in rats

BACKGROUND

The embryologic and pathologic aspect of anorectal malformation (ARM) remains poorly understood. There is no universally accepted theory to explain anorectal embryology and the abnormal development that produces ARM. The aim of this study was to observe the developmental processes of anorectum in rats and to explore the abnormal embryonic development that leads to ARM.

METHODS

Rat embryos with ARM were obtained by treating pregnant rats with administration of ethylenethiourea (ETU). Normal rat embryos and embryos with ARM from gestational days 12.5 to 20 were sectioned serially and sagittally and stained with H & E. The relevant structure including cloaca and urorectal septum (URS) were examined in a temporospatial sequence.

RESULTS

Characteristics of anorectum development in ARM rat embryos treated by ETU were as follows: (1) URS never fused with cloaca membrane. (2) Dorsal cloacal membrane was maldeveloped. (3) Cloacal configuration was abnormal. (4) Tail groove never appeared. All type of ARM was the rectourethal fistula and common cloaca in ETU-treated rat embryos and was discernible on gestation day 16.

CONCLUSIONS

Absence of the tail groove and maldevelopment of the dorsal cloacal membrane, cloacal configuration, and urorectal septum are likely to be responsible for the formation of ARM. Failure of fusion of the URS with cloacal membrane is the immediate reason for rectourethral fistula or common cloaca in ETU-treated rats.

The timing of enteric neural crest cell colonisation of the chick embryo cloaca

Neural crest cell (NCC) migration and formation of the enteric nervous system (ENS) is an essential process in the development of the normal human gut. Abnormalities of the ENS lead to a number of neurochristopathies. In avian embryos, the cloaca acts as a common chamber into which gastrointestinal, urinary and genital tracts emerge. Previous studies have elucidated the specific timeframes at which NCCs reach the various regions of the developing chick gut but, to date, none have looked at NCC colonisation of the cloaca. The aim of our study was to investigate the exact timing of the appearance of NCCs in the cloaca of chick embryos. Chicken embryos were harvested on embryonic days (E) 8-12. Whole embryos were fixed, embedded in paraffin and sectioned. Fluorescent immunohistochemistry, using an anti-HNK-1/N-CAM monoclonal antibody, was performed and images were obtained by confocal microscopy. There was no evidence of NCCs in the cloaca of embryos from E8 to E11. Intense immunoreactivity to HNK-1 first appeared in the cloaca of E12 embryos, demonstrating a profuse circumferential colonisation by NCCs at this time. Our study is the first to show the exact timing of enteric NCC colonisation of the chick embryo cloaca. Further studies, involving quail-chick chimeras, are required to establish the true origin of cloacal NCCs and to establish the relationship between NCCs and persistent cloaca.

The development of the male genitourinary system. I. The origin of the urorectal septum and the formation of the perineum

The embryological development of the male urinary system remains a subject of much controversy. As a result the pathogenesis of congenital anomalies such as hypospadias and epispadias, which are presented to the reconstructive surgeon remains poorly understood. A review of the literature identifies its three principal developmental stages: (1) division of the cloaca into the urogenital sinus and hindgut by the urorectal septum and the formation of the perineum; (2) the extension of the cloaca and its epithelium in the form of the urethral plate through the developing genital tubercle; (3) the separation of this extension from the surface during the formation of the urethra. This study, which uses a mouse model, examines these developmental stages in detail and together with a comprehensive review of the literature resolves many of the controversies relating to the development of the male urinary system. It reveals new insights into the origin of the associated congenital defects.

The absence of lateral fusion in cloacal partition

BACKGROUND/PURPOSE

The mechanism by which the cloaca becomes partitioned into a dorsal rectal part and a ventral genitourinary sinus has been the subject of speculation for more than a century. Despite repeated suggestions that partitioning of the cloaca by fusion of lateral folds does not occur, the concept continues to hold sway in many student and surgical texts. The authors reviewed the histologic and 3-dimensional appearance of the urorectal septum in human and rat embryos to see if there was any evidence of lateral fusion in its formation.

METHODS

Sprague-Dawley rat embryos (n = 143) were examined between 11 and 21 days' gestation and compared with human embryo sections (57 embryos) held in historical collections in Europe. Rat embryos were examined by microscopy, dissection, and serial histologic section. In addition, some specimens were sectioned in wax until the lumen of the cloaca was reached, after which they were dewaxed and the internal cavities imaged with scanning electronmicroscopy (n = 18 of 143).

RESULTS

Cloacal "partitioning" resulted from a combination of growth of the mesenchyme of the hindgut and genitourinary sinus, an alteration in the position of the cloaca in relation to surrounding structures secondary to growth in the ventral, infraumbilical abdominal wall and changes in the curvature of the developing spine, and apoptosis in the dorsal wall of the cloaca with shortening of the dorsal cloacal wall. There was no septum, as it is usually defined, between the developing bladder and hindgut. There was no evidence on either histologic section or scanning electronmicroscopy of any process of fusion occurring between the 2 lateral folds within the lumen of the cloaca.

CONCLUSIONS

Lateral fusion of the side walls of the cloaca does not play a role in cloacal "partition." Development of the bladder and hindgut occurs by a process that involves growth, differentiation, and remodeling.

Development of the human Müllerian duct in the sexually undifferentiated stage

An embryological explanation for the development of the Müllerian duct still poses a major challenge. The development of this duct was investigated systematically in human embryos. Seven embryos (Carnegie stages 18-23) were serially sectioned in the frontal, sagittal, and transversal planes at a thickness of 10 microm and stained with hematoxylin and eosin (H&E) for histological analysis. In all observed embryos, the caudal end of the Müllerian duct was found to be intimately connected to the Wolffian duct. The opening of the Müllerian duct to the coelomic cavity was formed as the result of an invagination of the coelomic epithelium at Carnegie stage 18. The duct grew independently from the invagination during stages 19-23. The fused duct (uterovaginal canal) bifurcated at the caudal portion at Carnegie stages 22 and 23. This is the first description of the caudal portion of the fused Müllerian ducts separating again and returning to each of the Wolffian ducts in human embryos.

A chicken model to study the embryology of cloacal exstrophy

BACKGROUND/PURPOSE

The embryology of bladder and cloacal exstrophy is a mystery. Reasons for this are the lack of human embryos showing these malformations as well as the scarcity of appropriate animal models. Here, the authors present cases of cloacal exstrophies found in chick embryos subsequent to the application of suramin and trypan blue. This animal model might facilitate insight into the embryology of cloacal exstrophy.

METHODS

Fertilized chicken eggs were incubated at 38 degrees C and 75% humidity. Embryos were treated in ovo on incubation day 3. The egg shell was windowed, and solutions of suramin (stage 13, 2 x 40 microL/0.2%) or trypan blue (stage 14, 2 x 80 microL/0.03%) were injected into the coelomic cavity. The window was closed, and the embryos were reincubated until examination on incubation day 8. Fifty embryos were treated in each group.

RESULTS

Among the surviving embryos, cloacal exstrophy was found in 2 cases in the suramin-treated group (2 of 29, 6.9%) and in 4 cases in the trypan blue-treated group (4 of 20, 20%).

CONCLUSIONS

Suramin and trypan blue can induce cloacal exstrophy in chick embryos. The authors now are modifying their experimental protocols to increase the incidence of this malformation. This model might facilitate studies on the morphogenesis of cloacal exstrophy.

Wnt signaling components in the chicken intestinal tract

Wnt signal transduction has emerged as an increasingly complex pathway due to the numerous ligands, receptors, and modulators identified in multiple developmental systems. Wnt signaling has been implicated in the renewal of the intestinal epithelium within adult animals and the progression of cancer in the colon. The Wnt family, however, has not been explored for function during embryonic gut development. Thus, to dissect the role of Wnt signaling in the developing gastrointestinal tract, it is necessary to first obtain a complete picture of the spatiotemporal expression of the Wnt signaling factors with respect to the different tissue layers of the gut. Here, we offer an in depth in situ gene expression study of Wnt ligands, frizzled receptors, and frizzled related modulators over several days of chicken gut development. These data show some expected locations of Wnt signaling as well as a surprising lack of expression of factors in the hindgut. This paper describes the first comprehensive characterization of the dynamic expression of Wnt signaling molecules during gut development. These data form the basis for future studies to determine the role of Wnt signaling in the developing gastrointestinal tract.

Anal canal development in the embryonic and early foetal period

The aim of study is to investigate the development of the anal canal in human embryos and foetuses. In embryos at stage 19 the boundary between the ectodermal and endodermal linings of the anal canal is located just below the level of the internal anal sphincter muscle. Histological sections showed that the first signs of anal columns are observed in embryos at stage 21 (51 days).

Clarification of the processes that lead to anorectal malformations in the ETU-induced rat model of imperforate anus

BACKGROUND

Ethylenethiourea (ETU) administered to timed-pregnant rats can induce anorectal malformations (ARMs) in about 80% of rat fetuses, thus providing an ideal animal model to study the embryogenesis of ARMs. The current study was undertaken to investigate the embryogenetic events that may be responsible for the development of ARMs in rats.

METHODS

Time-mated pregnant rats were divided randomly into control and experimental groups. The experimental rats received 1% ETU (125 mg/kg) by gavage on gestational day 10, and control rats received only the vehicle. Their embryos were harvested by cesarean section on gestational days 13, 14, 15, and 16. They were fixed and embedded in paraffin and serially sectioned in either the sagittal or transverse plane. The sections were stained with H&E, examined, and photographed. The comparative morphogenesis of the hindgut, cloaca, and tailgut of age-matched embryos was studied.

RESULTS

The key abnormalities in the experimental embryos were: (1) maldevelopment of cloaca and urorectal septum with no sign of the fusion between the urorectal septum and the cloacal membrane, (2) delay of tailgut regression, (3) abnormal and massive apoptotic cell death involving the posterior cloacal wall, and (4) underdevelopment of the dorsal aspect of the cloaca and its membrane. The type of ARM that was developing was discernible by gestational day 15 and 16.

CONCLUSIONS

ARMs induced by ETU in rat embryos seem to be caused by the cumulative effect of aberrations in the development of several components of the hindgut and cloaca. Variation in the extent of maldevelopment of these structures may result in a spectrum of ARMs.

The urethral plate--does it grow into the genital tubercle or within it?

OBJECTIVE

To determine whether the urethral plate grows into the genital tubercle or develops within it.

MATERIALS AND METHODS

Sprague-Dawley rat embryos were examined at 11-21 days of gestation and compared with available human embryo sections. Rat embryos were examined by a combination of light microscopy, dissection, serial histological section and immunohistochemistry.

RESULTS

In rat embryos the urethral plate extended to the tip of the genital tubercle from the earliest stages of genital tubercle development. The plate formed from adherence in the sagittal plane of the inner walls of the primitive cloacal cavity. The urethral plate continued to extend to the tip of the genital tubercle throughout penile development in the male and developed a lumen ahead of the advancing perineal mesenchyme. In the female the perineal side of the urethral plate disintegrated by massive apoptosis. This loss of perineal substance allowed the genital tubercle to collapse on itself and left the urogenital opening at the base of the genital tubercle. Human embryos also showed the presence of the urethral plate at the tip of the genital tubercle throughout genital tubercle development.

CONCLUSION

The urethral plate forms ab initio within the genital tubercle and extends to the tip; it does not grow into the genital tubercle as is often described. The contribution of ectodermal ingrowth to urethral development at the tip of the penis is minimal.

Clarification of the process of separation of the cloaca into rectum and urogenital sinus in the rat embryo

BACKGROUND/PURPOSE

The normal process of division of the cloaca into a rectum and urogenital tract is still not fully understood. The main controversies relate to how the urorectal septum (URS) divides the cloaca and whether the URS fuses with the cloacal membrane. This study used a 3-dimensional reconstruction technique, combined with histologic correlation, to observe the developmental and septational processes of the cloaca of the normal rat embryo from gestational days 11 to 16.

METHODS

Normal rat embryos from gestational days 11 to 16 were sectioned serially both transversely and sagittally and stained with H&E. 3-dimensional reconstructions were performed on embryos younger than day 13.5. The relevant structures were examined in a temporo-spatial sequence.

RESULTS

The tailgut started to regress by apoptosis on day 12 in a cranio-caudal direction. The URS, first evident in day-12.5 embryos, extended and fused with the cloacal membrane on day 15 of gestation, completing the separation of the cloaca into rectum and bladder. Regression of the tailgut and ventral protrusion of the urogenital sinus markedly changed the configuration of the cloaca. The cloacal membrane did not break down until after it had fused with the URS.

CONCLUSIONS

These findings clarify the relative contributions made by active septation of the cloaca by the URS and configurational changes of the cloaca to produce a rectum and bladder. The URS fuses with the cloacal membrane before the anal and urogenital membranes break down.

Does the urorectal septum fuse with the cloacal membrane?

PURPOSE

Traditional theories of cloacal embryogenesis assume that the urorectal septum fuses with the cloacal membrane before the anal membrane disintegrates. However, recent observations in humans and other species raise doubt about this assumption. We determined whether urorectal septum fusion occurs in rats.

MATERIALS AND METHODS

Rat embryos were harvested at specific times between days 11 and 16 of gestation. We evaluated the morphology, growth and relationship of the urorectal septum to the cloacal membrane on serial histological sections.

RESULTS

The urorectal septum consistently fused with the cloacal membrane on day 15 of gestation before the cloacal membrane began to disintegrate.

CONCLUSIONS

In rats the urorectal septum fuses with the cloacal membrane, after which the urogenital membrane and anal membrane disintegrate by a process of apoptosis.

Apoptosis during regression of the tailgut and septation of the cloaca

PURPOSE

Apoptosis is involved in the embryonic morphogenesis of many organs. The current study was undertaken to ascertain the role of apoptosis during cloacal development in the rat.

METHODS

One hundred five rat embryos, ranging from gestational days 11 to 16, were sectioned serially in the transverse or sagittal planes and stained with H&E. The cloaca, urorectal septum, rectum, urogenital sinus, Wolffian ducts, and tailgut (TG) were examined consecutively in temporospatial sequence.

RESULTS

The tailgut immediately distal to the hindgut starts to regress by apoptosis on day 12 of gestation in a craniocaudal direction and has regressed completely by day 13.5. A large number of apoptotic cells and debris can be identified in the urorectal septum during cloacal septation. Vacuoles are formed by coalescence of apoptotic cells at the tip of urogenital sinus from day 15 to 16, and, at the same time, sporadic apoptotic bodies in the anal membrane contribute to its thinning.

CONCLUSION

Results of the current study confirm that apoptosis occurs in a specific temporo-spatial sequence in the hindgut and cloaca and appears to be an important mechanism in TG regression, uro-rectal separation, urethral opening, and rupture of the anal membrane.

New mouse models of congenital anorectal malformations

BACKGROUND/PURPOSE

The genetic, embryological, and pathogenetic aspects of hindgut development remain poorly understood. Recently, the morphogenetic pathway involving the Sonic hedgehog (Shh) gene has been shown essential to the normal development of many midaxial organs, including the foregut. This study reports genetically based murine models of congenital anorectal malformations (CAM) involving the Shh-responsive transcription factors, Gli2 and Gli3. Its purpose is to show the necessity of these 2 factors to normal hindgut development.

METHODS

Gli2-/- mutants were generated by a targeted deletion. Gli3-/- mutants are spontaneous mutants involving the Gli3 gene. Gli2-/- Gli3+/- mutants were generated by intercrossing double heterozygotes. Whole-mount midsagittal sections of the embryos were analyzed on embryonic days (E) 11.5 and E13.5.

RESULTS

Gli3-/- mutants had anal stenosis and ectopic anus, and Gli2-/- mutants showed imperforate anus and rectourethral fistula. Gli2-/- Gli3+/- mutants had a cloacal abnormality.

CONCLUSIONS

The phenotypic abnormalities observed in these mutant mice are identical to the spectrum of human CAM. The severity of the phenotype appears to reflect the gene dose. Gli2 and Gli3 play an important role in the normal development of murine hindgut. The results of this study provide, for the first time, a molecular basis for CAM.

Further study of the urorectal septum in staged human embryos

Study was carried out on serial section of 45 human embryos of stages 13 to 23. The urorectal septum develops from three folds: single superior and two lateral ones. Development of the urorectal septum begins at stage 13 when the superior fold between the hindgut and allontois appears. At stage 15, all three folds unite to from complete septum, reaching the cloacal membrane and dividing the cloaca into anterior compartment, the primary urogenital sinus and the posterior compartment rectum.

Bladder agenesis with urometrocolpos

A 20-day-old female presented in acute renal failure with an absent bladder and vaginal atresia. The right ureter opened into the uterus, resulting in a urometrocolpos, and the left ureter opened through a stenotic opening into the introitus. The literature is reviewed for reported cases and the embryo-pathology of bladder agenesis is discussed.

Septation and differentiation of the embryonic human cloaca

BACKGROUND/PURPOSE

Limitations in methodologies have fostered controversy regarding the septation of the human embryonic cloaca. The aim of this study was to evaluate the septation of the human embryonic cloaca.

METHODS

Using the Carnegie Embryological Collection and specimens at Johns Hopkins, Baltimore, MD, the authors studied 12 embryos and five fetuses. Embryo photomicrographs were reconstructed using three-dimensional modeling.

RESULTS

In Carnegie stage 13 the authors observed a cloaca, distinct primitive urogenital sinus, and anorectum separated by the urorectal septum. The primitive urogenital sinus and anorectum enter the cloaca separated from the amniotic space by the cloacal membrane. As the embryo becomes a fetus it lengthens, grows, expands and rotates through a process called transformation. Transformation gives rise to a loss of caudal curvature and a decrease in distance between the septum and membrane, but these structures do not fuse. Disintegration of the cloacal membrane produces openings for the urogenital sinus and anorectum.

CONCLUSIONS

The observations suggest that the urogenital sinus and anorectum form early and are separated by the urorectal septum as a passive structure. There does not appear to be septation or differentiation of the cloaca itself.

Chick Barx2b, a marker for myogenic cells also expressed in branchial arches and neural structures

We have isolated a new chicken gene, cBarx2b, which is related to mBarx2 in sequence, although the expression patterns of the two genes are quite different from one another. The cBarx2b gene is expressed in craniofacial structures, regions of the neural tube, and muscle groups in the limb, neck and cloaca. Perturbation of anterior muscle pattern by application of Sonic Hedgehog protein results in a posteriorization of cBarx2b expression.

Cloacal dysgenesis sequence: observations in four patients including three fetuses of second trimester gestation

Cloacal dysgenesis is a rare malformation sequence. We studied cloacal dysgenesis in four fetuses, including three at 18-22 weeks of gestation. All four fetuses showed a smooth perineum with absence of anal, urethral, and/or vaginal openings. The urinary bladder was dilated in 3 cases. The labia majora and minora were absent in the two female fetuses; the scrotum and penis were absent in one male fetus and hypoplastic in the second. The kidneys were either absent (1 case), dysplastic (1 case), or hydronephrotic (1 case). Normal kidneys were seen in a fetus of 20-22 weeks gestation in whom the urinary obstruction was alleviated by a vesicocolonic fistula. This fetus did not have pulmonary hypoplasia. Severe renal anomaly and pulmonary hypoplasia are the limiting factors for the survival of infants born with cloacal dysgenesis. The unique observation of normal kidneys and lungs in one of our fetuses, despite anhydramnios, suggests that the effect of oligohydramnios on lung development may be limited early in gestation, at least up to 20-22 weeks. It may also indirectly support the theory that there are factors other than oligohydramnios that interfere with early lung development, such as reduced production of a pulmonary growth factor by the kidney or reduced proline production by malformed kidneys, that may cause decreased collagen formation and result in hypoplastic lung mesenchyme.

Normal and abnormal embryonic development of the anorectum in human embryos

In the literature, some controversy still exists about the normal and abnormal development of the human anorectum. Therefore, a three-dimensional and histological study was performed on human embryos. In early anorectal development (< or = 49 days postfertilization), the cloaca plays a crucial role, separated from the amniotic cavity by its cloacal membrane. In the cloaca, the yolk sac/primitive hindgut and allantois/primitive urogenital sinus enter. During the embryonic caudal folding process, incorporation of these structures occurs, including their surrounding extraembryonic mesoderm, which fuses to form the urorectal septum. Consequently, this septum does not grow in the direction of the cloacal membrane, and fusion of these structures is likewise never observed. The cloaca remains as such until the cloacal membrane ruptures by apoptotic cell death. The dorsal part of the cloaca then becomes part of the amniotic cavity, and is by no means involved in the development of the anorectum. The tip of the urorectal septum will become the perineal area. Soon after rupture of the cloacal membrane, during late anorectal development (> or = 49 days postfertilization), a secondary occlusion of the anorectal canal occurs, first due to adhesion, followed by formation of an epithelial "plug" at the level of the anal orifice. Recanalization, by apoptotic cell death, of this secondary occluded anal orifice occurs later during development. Based on these embryological observations, congenital anorectal malformations with an abnormal communication to the exterior are best explained as early embryonic defects. The abnormal communications, usually called fistulae, should be regarded as ectopic anal orifices. Anorectal malformations with the anus in normal position are best explained as late embryonic defects.

First-trimester prenatal sonographic findings associated with OEIS (omphalocele-exstrophy-imperforate anus-spinal defects) complex: a case and review of the literature

First-trimester sonographic findings associated with omphalocele-exstrophy-imperforate anus-spinal defects (OEIS) complex and review of the literature regarding this rare congenital anomaly are presented.

Current concepts in the embryology of anorectal malformations

Today, the normal and abnormal development of the hindgut is still a matter of speculation. However, owing to recent studies in appropriate animal models, most embryological events that finally lead to abnormal hindgut development are better known than in the past: (1) The process of maldevelopment starts early in the embryo. (2) The cloacal membrane always is too short in its dorsal part. Thus the dorsal cloaca is missing too. (3) As a result, the hindgut remains attached to the sinus urogenitalis, thus forming the recto-urethral fistula. In the past, an impaired process of septation was believed to be the main cause of abnormal hindgut development. In contrast to this, our results indicate that the development of the septum is more passive than active. Further results of our studies in normal and abnormal development indicate that (1) the embryonic cloaca never passes through a stage that is similar to any form of anorectal malformation in neonates, including the so-called "cloacas" in females, and (2) to explain abnormal development, studies in abnormal embryos are mandatory.