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.

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.

Adenocarcinoma arising in a rectal duplication cyst with distant metastasis A case report and a review of the recent literature

INTRODUCTION

Rectal duplication cysts are rare cystic lesions, arising from the hindgut and classified as congenital/developmental tumors of the presacral space. Their clinical presentation is nonspecific, the diagnosis remains difficult and their management is aided by a multidisciplinary evaluation.

CASE REPORT

We report the case of a 55-year-old woman with a cystic mass located in the retrorectal space and identified incidentally on a CT scan. Following imaging studies, surgical resection by a posterior approach (Kraske procedure) was carried out and an adenocarcinoma arising in a duplication cyst of the rectum was present an uncommon case of a rectal duplication cyst with malignant transformation and distant metastasis, describe the clinical, radiologic and pathologic findings and discuss tidentified by microscopy.

CONCLUSION

We phe embryological basis of rectal duplication cysts and the surgical anatomy of the presacral space. Key Words: Rectal adenocarcinoma, rectal duplication cyst, Retrorectal space.

Whole mount microscopic sections reveal that Denonvilliers' fascia is one entity and adherent to the mesorectal fascia; implications for the anterior plane in total mesorectal excision?

BACKGROUND

Excellent anatomical knowledge of the rectum and surrounding structures is essential for total mesorectal excision (TME). Denonviliers' fascia (DVF) has been frequently studied, though the optimal anterior plane in TME is still disputed. The relationship of the lateral edges of DVF to the autonomic nerves and mesorectal fascia is unclear. We studied whole mout microscopic sections of en-bloc cadaveric pelvic exenteration and describe implications for TME.

METHODS

Four donated human adult cadaveric specimens (two males, two females) were obtained from the Leeds GIFT Research Tissue Programme. Paraffin-embedded mega blocks were produced and serially sectioned at 50 and 250 μm intervals. Sections were stained with haematoxylin & eosin, Masson's trichrome and Millers' elastin. Additionally, a series of eleven human fetal specimens (embryonic age of 9-20 weeks) were studied.

RESULTS

DVF consisted of multiple fascial condensations of collagen and smooth muscle fibres and was indistinguishable from the anterior mesorectal fascia and the prostatic fascia or posterior vaginal wall. The lateral edges of DVF appeared fan-shaped and the most posterior part was continuous with the mesorectal fascia. Fasciae were not identified in fetal specimens.

CONCLUSION

DVF is adherent to and continuous with the mesorectal fascia. Optimal surgical dissection during TME should be carried out anterior to DVF to ensure radical removal, particularly for anterior tumours. Autonomic nerves are at risk, but can be preserved by closely following the mesorectal fascia along the anterolateral mesorectum. The lack of evident fasciae in fetal specimens suggested that these might be formed in later developmental stages.

Abnormal neural crest innervation in Sox10-Venus mice with all-trans retinoic acid-induced anorectal malformations

BACKGROUND/PURPOSE

Despite technical advances in the surgical/medical care of anorectal malformation (ARM), persistent unsatisfactory postoperative bowel habit has been attributed to histopathologic abnormalities of the distal rectum/pouch (DRP) and hypoplasia of anal sphincter muscles (ASM). We used Sox10-Venus mice with ARM induced by all-trans retinoic acid (ATRA) to investigate neural crest cell (NCC) innervation in the DRP and ASM.

METHOD

Pregnant Sox10-Venus mice were administered single doses of 50, 70, or 100 mg/kg of ATRA on embryonic day 8.5 (E8.5) then sacrificed on either E16.5 or E19.5. Bowel specimens comprising the anorectum were examined using fluorescence microscopy without immunohistochemical staining (FMIS). Anti-PGP9.5 was used to delineate ganglion cells and anti-SMA for smooth muscles.

RESULTS

The appropriate dose of ATRA for inducing ARM was 50 mg/kg. Under FMIS, all ARM embryos (n = 5; all high type; 3 male:2 female) had less NCC innervation with thick Venus-positive nerve fibers in the DRP compared with normal embryos (n = 8); there was abnormal NCC innervation in the DRP and absent ASM in ARM mice.

CONCLUSION

We are the first to delineate abnormal enteric nervous system innervation in the DRP of ARM mice without using immunohistochemical staining techniques thus allowing specimens to be examined without any distortion.

Anococcygeal raphe revisited: a histological study using mid-term human fetuses and elderly cadavers

PURPOSE

We recently demonstrated the morphology of the anococcygeal ligament. As the anococcygeal ligament and raphe are often confused, the concept of the anococcygeal raphe needs to be re-examined from the perspective of fetal development, as well as in terms of adult morphology.

MATERIALS AND METHODS

We examined the horizontal sections of 15 fetuses as well as adult histology. From cadavers, we obtained an almost cubic tissue mass containing the dorsal wall of the anorectum, the coccyx and the covering skin. Most sections were stained with hematoxylin and eosin or Masson-trichrome solution.

RESULTS

The adult ligament contained both smooth and striated muscle fibers. A similar band-like structure was seen in fetuses, containing: 1) smooth muscle fibers originating from the longitudinal muscle coat of the anal canal and 2) striated muscle fibers from the external anal sphincter (EAS). However, in fetuses, the levator ani muscle did not attach to either the band or the coccyx. Along and around the anococcygeal ligament, we did not find any aponeurotic tissue with transversely oriented fibers connecting bilateral levator ani slings. Instead, in adults, a fibrous tissue mass was located at a gap between bilateral levator ani slings; this site corresponded to the dorsal side of the ligament and the EAS in the immediately deep side of the natal skin cleft.

CONCLUSION

We hypothesize that a classically described raphe corresponds to the specific subcutaneous tissue on the superficial or dorsal side of the anococcygeal ligament.

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.

Sonographic evaluation of the development of the fetal rectum and anal canal

PURPOSE

To describe the sonographic (US) appearance of fetal anal canal and rectum and establish nomograms of their normal measurements.

METHODS

This was a prospective, cross-sectional study of 524 healthy women (mean age, 27 years; range, 21-37 years) with normal singleton pregnancy between 18 and 40 weeks of gestational age (GA). High-resolution transabdominal US was used to visualize and measure the normal fetal anal canal and rectum.

RESULTS

Satisfactory images and measurements of the fetal anal canal and rectum were obtained in 496 normal fetuses. The diameters of the normal anal canal and rectum were plotted as a function of GA in a sigmoid curve. The curve estimations were expressed by the following cubic regression equations with R(2) of 0.87 and 0.88, respectively (p < 0.001): anal canal diameter (mm) = 18.272 - 2.151 × GA + 0.0095 × GA(2) - 0.0011 × GA(3) , and rectal diameter (mm) = 18.545 - 2.543 × GA + 0.1237 × GA(2) - 0.0016 × GA(3) .

CONCLUSIONS

The fetal anal canal and rectum are visible sonographically between 18 and 40 weeks of GA. The knowledge of their normal US appearance and size from the second trimester of pregnancy onwards may help identify developmental anomalies.

Apoptosis during the development of pelvic floor muscle in anorectal malformation rats

PURPOSE

Fecal incontinence and constipation still remain as major postoperative complications after procedures for anorectal malformations (ARM). The striated muscle complex (SMC) is one of the most important factors that influence defecation. Previous studies have demonstrated different degrees of the muscle complex dysplasia dependent on the complexity of ARM. To explore the mechanisms of maldevelopment of SMC in ARM, apoptosis was investigated during pelvic floor muscle development in rat embryos with ARM.

METHODS

Anorectal malformations in rat embryos were induced by treating pregnant rats with ethylenethiourea on the 10th embryonic day (E10). Normal and ARM rat embryos from E16 to E21 were serial-sectioned transversely or sagittally, and SMCs were dissected and snap frozen. TdT mediated dUTP Nick Ending Labeling (TUNEL) staining and DNA ladder analysis were performed to identify apoptosis and expression of Bax/Bcl-2 were confirmed with immunohistochemical staining and Reverse Transcription-Polymerase Chain Reaction (RT-PCR) analysis.

RESULTS

Hypoplastic and disordered SMC sling shifted cephalad, ventrally, and converged inferior to the rectourethral fistula and infiltrated connective tissue in ARM embryos. In the normal group, TUNEL-positive cells became evident on E17; sporadic positive staining was mainly localized in 2 areas as follows: the junction area between SMC and bulbocarvernosus muscle and posterior to the rectum where bilateral SMC converged. In the ARM group, massive positive staining of nuclei was observed from E16 to E21 and was mainly distributed in the dorsal part of the SMC. Electrophoresis of DNA samples yielded a "ladder" pattern of migration both in normal and the ARM group from E17 to E21, the ladders were stronger in the ARM group. In both groups, the expression of Bax/Bcl-2 was detectable on E17, the immunoreactivity increased on E19 and E21. Compared with the normal group, the expression of Bax was increased, whereas Bcl-2 was declined in the ARM group. Significant upregulation of Bax messenger RNA (mRNA) levels and downregulation of Bcl-2 mRNA levels were observed in ARM embryos.

CONCLUSIONS

In the current study, abnormal apoptosis and disturbed expression of Bax/Bcl-2 were identified during SMC development in ARM embryos. It is suggested that precocious, excessive, and dislocated apoptosis might be a fundamental pathogenesis for the maldeveloped SMC in ARM rats. The temporospatial expressions of Bax/Bcl-2 indicate they may have an important role in the regulation of apoptosis of SMC.

Evaluation of an experimental model for anorectal anomalies induced by ethylenethiourea

PURPOSE

To evaluate an experimental model for anorectal anomalies and their principal associated malformations induced by ethylene thiourea (ETU).

METHODS

Rat fetuses were utilized, divided into two groups: experimental group - fetuses from rats that received ETU on the 11th day of gestation at the dose of 125 mg/kg, diluted in distilled water to 1% concentration (12.5 ml/kg); and control group - fetuses from rats that received distilled water alone, at a volume of 12.5 ml/kg. On the 21st day of gestation, the animals were sacrificed by hypoxia in a carbon dioxide chamber, followed by laparotomy to remove the fetuses. These were initially examined externally to determine the sex and whether anorectal anomalies and malformations of the vertebral column and tail were present. Then, with the aid of microscopy, the fetuses underwent exploratory laparotomy to characterize the type of anorectal anomaly and investigate urological malformations.

RESULTS

None of the fetuses in the control group presented anorectal anomaly, vertebral column malformation or urological structural alterations. In the experimental group, 71% presented anorectal anomaly, 80% presented vertebral column alterations and 35% presented urological alterations.

CONCLUSION

The model described was shown to be easy to implement and presented results that allow its use in studying anorectal anomalies and associated malformations.

Epithelial and muscular regionalization of the human developing anorectum

In the past, interpretations of anorectal development were mainly based on analysis of serially sectioned embryos of various nonhuman species as well as some human specimens. A four-dimensional view of the developmental situation in the human has never been established nor connected to recent findings obtained from newer molecular techniques. We, therefore, investigated human embryonic and fetal pelves by means of immunohistochemistry and in situ hybridization to elucidate differentiation and interaction of epithelial and mesenchymal layers of the anorectum. To emphasize spatial as well as sequential morphological development, we produced three-dimensional reconstructions of the specimens at hand. Research conducted proved that the decisive steps of epithelial and muscular differentiation occur between the 7th and 9th week after conception. This study elucidates a biphasic epithelial "closure" in the anal canal and interactions between epithelium, smooth musculature, and skeletal musculature. Based on the results presented here, it is possible to describe the pathogenesis of two anorectal malformations: the imperforate anal membrane and the anal membrane stenosis. This study will now provide the basis for further research into developmental processes occurring before the ones examined.

Anatomical considerations in TNM staging and therapeutical procedures for low rectal cancer

BACKGROUND

Separation of the mesoderm-derived muscular structures and the endoderm-derived structures of the hindgut and reclassification of their involvement based on their embryological origin may be of clinical importance in providing anatomical support for a more standardized perineal resection during abdominoperineal resection. The aim of this study was to utilize magnetic resonance images and histological studies of fetal and neonatal specimens to redefine the T3/T4 distinction by reassessment of the intersphincteric plane and the pelvic diaphragm as they pertain to cancer infiltration and as part of the embryological development of the pelvic floor muscles and their connective tissue compartments.

MATERIALS AND METHODS

Pelvic floor anatomy was studied in seven newborn children and 120 embryos and fetuses. Anatomical data were completed by magnetic resonance imaging in 82 patients with T3 and T4 rectal cancers (64 T3, 18 T4; 35 women and 47 men) undergoing neoadjuvant chemoradiation for locally advanced (T3 or T4) rectal cancers.

RESULTS

Clear demarcation between mesodermal and endodermal structures of the pelvic floor, which is equally evident in plastinated sections and magnetic resonance images, is already visible in early fetal stages. There is a constitutive overlap between the endoderm- and the ectoderm-derived components of the pelvic floor.

CONCLUSION

Our data suggest that the current classification of rectal cancer staging is confusing, where the routinely used TNM classification system unnecessarily differentiates between embryologically identical muscular structures. Tumor spread along the musculature of the hindgut beyond the dentate line could possibly explain the occasional involvement of lymph nodes outside the conventional mesorectum.

The mesorectum: hypothesis on its evolution

BACKGROUND

Two points are controversial in the anatomy of the mesorectum: (1) its origin; and (2) the existence of the lateral ligaments. We studied these structures in animals and in human fetuses.

METHODS

Dissections were performed on quadrupedal mammals (29 dogs and 32 pigs) and 28 primates (Macaca apes). Moreover, macroslices of Macaca ape and of 182 human fetuses were examined histologically.

RESULTS

In quadrupedal mammals, we found no traces of any adipose masses comparable to the human mesorectum nor were there ligaments of suspension. In the ape, the adipose tissue in the mesosigmoid forms an adipose cuff that completely surrounds the extraperitoneal rectum. Two dense connective bands were found between the lateral wall of the pelvis and the perirectal tissue. Both the mesorectum and the lateral ligaments were clearly identified in the sections of human fetus only at the end of the fifth month but not earlier.

CONCLUSIONS

On the basis of our analysis of 3 animal species, we conclude that the mesorectum and lateral ligaments are absent in quadrupedal mammals but are present in primates. Therefore, we hypothesize that these structures appeared with the attainment of the upright position, even though other hypotheses are possible.

The murine homolog of SALL4, a causative gene in Okihiro syndrome, is essential for embryonic stem cell proliferation, and cooperates with Sall1 in anorectal, heart, brain and kidney development

Mutations in SALL4, the human homolog of the Drosophila homeotic gene spalt (sal), cause the autosomal dominant disorder known as Okihiro syndrome. In this study, we show that a targeted null mutation in the mouse Sall4 gene leads to lethality during peri-implantation. Growth of the inner cell mass from the knockout blastocysts was reduced, and Sall4-null embryonic stem (ES) cells proliferated poorly with no aberrant differentiation. Furthermore, we demonstrated that anorectal and heart anomalies in Okihiro syndrome are caused by Sall4 haploinsufficiency and that Sall4/Sall1 heterozygotes exhibited an increased incidence of anorectal and heart anomalies, exencephaly and kidney agenesis. Sall4 and Sall1 formed heterodimers, and a truncated Sall1 caused mislocalization of Sall4 in the heterochromatin; thus, some symptoms of Townes-Brocks syndrome caused by SALL1 truncations could result from SALL4 inhibition.

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.

Prenatal diagnosis of fetal hydrometrocolpos secondary to a cloacal anomaly by magnetic resonance imaging

Fetal female urogenital anomalies are often difficult to evaluate by ultrasonography, especially in late gestation. We report a case of fetal hydrometrocolpos detected at 35 weeks of gestation. Ultrasonography revealed a large retrovesical septate hypoechogenic mass in the fetal abdomen, however the sonographic findings were inconclusive. Magnetic resonance imaging (MRI) confirmed that the abdominal mass was fluid-filled with a mid-plane septum in the midline posterior to the bladder, and showed a connection to the dilated uterus that was duplicated. These findings were consistent with a diagnosis of hydrometrocolpos with septate vagina and uterus didelphys. The neonate showed abdominal distension, ambiguous genitalia and anal atresia with a single perineal opening. Hydrometrocolpos was secondary to a urethral type of cloacal anomaly. Aspiration of the mass and a colostomy were performed on the first postnatal day, followed by anorectoplasty at 19 months of age. MRI is a useful complementary tool for assessing fetal urogenital anomalies when ultrasonography is inconclusive.

Impaired expression of myogenic regulatory molecules in the pelvic floor muscles of murine embryos with anorectal malformations

BACKGROUND/PURPOSE

Recent biological studies have elucidated the molecular mechanism of muscle development, in which various regulatory factors (myogenic regulatory factors [MRFs]) play key roles during embryogenesis. To investigate the development of anorectal malformations (ARMs), we studied MRF expressions in myogenic cells in the pelvic floor using murine embryos affected with ARM.

METHODS

Anorectal malformation embryos were obtained from the 10.5th embryonal day (E10.5) to the 7.0th postnatal day (D7.0) in a natural mutant strain (Sd/+, RSV/Le). Serial frozen sections were prepared for immunohistochemistry using specific antibodies to M-cadherin, myoD, Myogenin, myosin heavy chain, and alfa-actin molecule.

RESULTS

In normal mice, embryonal caudal somites differentiated into myogenic stem cells and migrated to the pelvic floor between E11.0 and E14.0. In the ARM mice, however, caudal somites were irregularly arranged and MRF expressions in myogenic cells were markedly decreased in the dorsocaudal region at E11.5 to E13.0, leading to hypoplastic pelvic floor muscles.

CONCLUSIONS

The maldevelopment of pelvic floor muscles in ARM is derived from a deficient supply of myogenic stem cells, with impaired MRF expression. These results suggest that myogenic stem cells, available from bone marrow contents, may be used for postnatal muscle regeneration to reinforce the pelvic floor muscle function in children with ARM.

Aberrations of the intrinsic innervation of the anorectum in fetal rats with anorectal malformations

BACKGROUND

Fecal accumulation, constipation, soiling, and incontinence are common sequelae after repair of anorectal malformations (ARMs) in children. It is believed that besides the abnormalities of sacral roots, certain inherent abnormalities of the myenteric plexuses may play an important role in the final outcome after definitive repair.

METHODS

This study was conducted to investigate the distribution of neuron-specific enolase (NSE), vasoactive intestinal peptide (VIP), and substance P (SP)-100 neurotransmitters in the rectosigmoid and fistulous tract of the ethylenethiourea-treated rat with ARMs.

RESULTS

ARMs were induced by administering 1% ethylenethiourea (125 mg/kg) on gestational day 10, and the litter was harvested on gestational day 21 by cesarean section. Forty-eight controls and 63 with ARMs (46 high-type and 17 low-type) were recovered. Whole-mount preparations of each rectosigmoid and fistulous communication between the rectum and genitourinary tract were stained with fluorescent antibodies against NSE, VIP, and SP-100. The tissues were counterstained with Eriochrome black-T and methyl green dyes to improve the visualization of the myenteric plexuses.

CONCLUSIONS

The immunoreactivity of NSE, VIP, and SP-100 was markedly reduced in the rectum and fistulous tract of high-type ARMs and slightly reduced in low-type ARMs compared with controls. Intramural nerves stained by VIP and SP-100 antisera were decreased in both types of ARM, indicating that both inhibitory and excitatory motor neural elements were affected, and this may explain the distal colonic dysmotility seen postoperatively in both high and low ARMs.

AN EMBRYOLOGICAL STUDY OF FETAL DEVELOPMENT OF THE RECTOURETHRALIS MUSCLE—DOES IT REALLY EXIST?

PURPOSE

The so-called rectourethralis muscle is widely described in the urological literature. However, its description is subject to variations concerning extent and morphology. Moreover, little is known about its fetal development, which would allow a better understanding of the adult anatomy. The aim of this study was to investigate the morphology, extent and development of the rectourethralis muscle in fetal specimens.

MATERIALS AND METHODS

A total of 15 normal human male fetuses were included in the study. Age ranged from 13th week of gestation to term. The histological study used plastination and standard and immunohistochemical techniques to identify the developing muscular structures in serial sections of the rectourethral space. Investigations in all 3 planes (coronal, sagittal and transverse) were performed.

RESULTS

In all sections of the proximal aspect of the rectourethral space no developing muscle fibers could be identified leaving the anterior wall of the rectum to join the rhabdosphincter or the apical prostate. In the distal aspect of the rectourethral space an independent muscular structure located between the external muscular layer of the anorectal canal and the dorsal bundles of the rhabdosphincter could be clearly demonstrated. This structure consisted of connective, smooth and striated muscle tissue, and was deeply anchored to the apical perineal body.

CONCLUSIONS

This study suggests that the so-called rectourethralis muscle is a misnomer in the urological literature. In the fetal period a developing muscular structure could be clearly identified as a part of the apical perineal body, which would correspond to the rectoperinealis muscle in the adult.

Congenital segmental dilatation of the colon with anorectal malformation

Segmental dilatation of the colon is a rare entity. The authors report unique case of segmental dilatation of the cecum and ascending colon with high anorectal malformation in a newborn, and the possible embryogenesis of this condition is discussed.

Anorectal anatomy and embryology

The anal canal is complex in its anatomy and its embryologic origin. The intricate and changing histology of the anal canal explains the different types of anal cancer. In addition, an understanding of the venous and the lymphatic drainage of the anal canal helps to explain its methods of dissemination. Finally, the basis for the treatment of anal cancer is derived from the cancer's anatomic origins.

Fibroblast growth factor 10 (Fgf10) invalidation results in anorectal malformation in mice

BACKGROUND/PURPOSE

Anorectal malformations occur in 1 per 4,000 live births and represent a surgical challenge. Although critically important, the basic mechanisms of normal anorectal union are incompletely understood. Fgf10 signaling is known to serve a key role in mesenchymal/epithelial interactions in many organ systems including the gastrointestinal tract (GIT). The authors therefore hypothesized that Fgf10 signaling has a central role in normal anorectal development.

METHODS

Fgf10 expression in wild-type (Wt) embryos was evaluated using whole-mount in situ hybridization. Wt and Fgf10-/- embryos were harvested from timed pregnant mothers at E12.5 through E17.5 and were analyzed for anorectal phenotype.

RESULTS

Wt development of union between anorectal structures is completed between E12.5 and E13.5 with luminal communication between distal rectal epithelium and anus. Fgf10 is discretely expressed at E12.5 in the distal rectum. Fgf10-/- mutants show failure of union of the rectum and anus at an early stage (E13.5) and near term (E17.5).

CONCLUSIONS

Fgf10 is expressed in the rectum at the time when anorectal continuity is established, indicating a role in normal anorectal development. Fgf10 invalidation (Fgf10-/- mutant) results in a genetically reproducible anorectal malformation phenotype. Fgf10 function is critical for normal anorectal development.

The rectogenital septum: morphology, function, and clinical relevance

PURPOSE

The rectogenital septum (known in clinical literature as Denonvilliers' fascia) forms an incomplete partition between the rectum and the urogenital organs in both men and women. It is composed of collagenous and elastic fibers and smooth muscle cells intermingled with nerve fibers emerging from the autonomic inferior hypogastric plexus. The aim of this study was to investigate the fetal development of the rectogenital septum, and the origin and innervation of the longitudinal smooth muscle cells within the septum, as well as to consider possible effects on function of operations that compromise the integrity of these structures.

METHODS

Macroscopic dissections on embalmed human pelves and plastination histology of 40 fetal and newborn pelvic specimens were performed. By means of conventional and immunohistochemical staining methods using monoclonal and polyclonal antibodies for tissue analysis and neuronal labeling, the motor and sensory innervation of the longitudinal muscle bundles within the septum was defined.

RESULTS

The rectogenital septum is formed by a local condensation of mesenchymal connective tissue in the early fetal period. The longitudinal muscle bundles could be traced back to the longitudinal layer of the rectal wall, and, using the septum as a guiding structure, it was possible to identify autonomic nerve fibers and ganglion cells innervating the muscle cells and crossing the midline without detectable gender differences.

CONCLUSIONS

Because of a coinnervation of the rectal muscle layers and the adjacent longitudinal muscle fibers of the septum, a functional correlation between the two structures during defecation is postulated. On the basis of these findings, a safer dissection of the anterior rectal wall during rectal resection is postulated, thus limiting functional disturbance and preventing neural damage.

Sonic hedgehog and bone morphogenetic protein 4 expressions in the hindgut region of murine embryos with anorectal malformations

PURPOSE

The aim of this study was to determine the possible role of the retinoid-mediated signaling pathway in the pathogenesis of anorectal malformations (ARM). The authors investigated whether all-trans retinoic acid (ATRA) affects the expression pattern of Sonic hedgehog (Shh) and Bone morphogenetic protein 4 (BMP4), which play important roles in anorectal morphogenesis in vertebrates.

METHODS

Pregnant ICR strain mice were fed 100 mg/kg of ATRA on the ninth gestational day (E9). Embryos with or without administration of ATRA were obtained from the uteri between E12 and E16 and were fixed immediately in a 4% paraformaldehyde solution. Frozen sections were evaluated for concentric layers around the endodermal epithelium by H&E and immunohistochemistry using antibodies created specifically to act against Shh and BMP4.

RESULTS

More than 95% of the embryos administered ATRA had ARM; rectoprostatic urethral fistula, rectocloacal fistula, and short tail were the most frequent anomalies in the mouse embryos. On E14, normal mouse embryos had normal rectum and anus in which the epithelium of the anorectum was positive for Shh, and the mesenchyme was positive for BMP4. In the ARM embryos, however, the epithelium of the anorectum was negative for Shh, and the mesenchyme was also negative for BMP4.

CONCLUSIONS

In normal hindgut development, Shh from the epithelium induces BMP4 expression in the mesenchyme, which differentiates into the lamina propria and the submucosa. In ARM embryos, expressions of Shh and BMP4 could not be found in those regions of the hindgut. Therefore, these findings indicate that Shh and BMP4, which appear to play a crucial role in organogenesis of the hindgut, were disturbed in the cell signaling pathway between the epithelium and the mesenchyme layers.

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.

Congenital diaphragmatic hernia and chromosomal anomalies: autopsy study

In a 10-year review of autopsy records from Lutheran General Hospital (1992-2002), 13 cases of congenital diaphragmatic hernia (CDH) were found. The fetuses ranged between 21 and 35 wk of gestation. Four were born alive and five were diagnosed prenatally. The defect was left-sided in 11 cases. Cytogenetic study revealed five cases with normal karyotype and three cases with complex karyotypes. In five cases, no karyotype was performed. The three complex karyotypes were: 46,XX,del(8)(p23.1), 47,XX, +i(12)(p10)[6]/46XX[14] (Pallister-Killian syndrome), and 47,XY,+der(22)t(11:22) (q23.3:q11.2). The unbalanced translocation of chromosomes 11 and 22 in congenital diaphragmatic hernia has not been previously described. Three fetuses had heart abnormalities, including one which was associated with the 8p deletion. The other two had no karyotype study. Neither in this study, nor in the literature, is there a consistent or prevailing association between a specific chromosomal anomaly and CDH. The embryologic closure of the diaphragmatic leaflets may be mediated by a nonstructural chromosomal defect, more than one gene, and/or may be related to abnormalities not currently detectable.

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.

Perirenal tailgut cyst (cystic hamartoma)

Tailgut cysts are rare congenital multicystic lesions preferentially occurring in the retrorectal space. They are assumed to arise from the remnant of embryonic tailgut and occasionally exhibit malignant transformation. The authors herein describe the clinical, radiologic, and pathologic features of an unusual perirenal tailgut cyst with an emphasis on its histogenesis and distinction from other intraabdominal cystic lesions.

Expression of adhesion molecules in the rectum-associated lymph nodules of pre- and postnatal specific pathogen-free rats

BACKGROUND AND AIM

The developmental process of lymphoid tissues in the gastrointestinal tract is still unclear. The aim of the present study was to explore the expression of adhesion molecule in rectum-associated lymph nodules (RALN) of specific pathogen-free (SPF) rats at fetal and early postnatal periods of development.

METHODS

Immunohistochemical analysis was carried out of select adhesion molecules and lymphocyte subsets in lymph nodules of the rat rectal region.

RESULTS

Mucosal addressin cell adhesion molecule (MAdCAM)-1 expression was detected in the colonic mucosa on day 16 of gestation. Expression was strong in endothelial cells of all blood vessels in the entire colonic mucosa until day 7 after birth. On day 10 after birth, MAdCAM-1 was strongly expressed and confined to the high endothelial venule (HEV) in the submucosa of RALN, and was rarely detected in the blood vessels other than the HEV. In contrast, intercellular adhesion molecule (ICAM)-1 expression was absent in fetal colonic mucosa but appeared just after birth. Only a very small number of lymphocyte-function associated antigen (LFA)-1-positive cells appeared in the mucosa on day 16 of gestation but by day 19 of gestation a large number of these cells had rapidly aggregated in the mucosa of the ante-mesenteric side of the developing colon. These cells also expressed interleukin-7 receptor (IL-7R), and some were positive for CD4 and Mar-1 markers.

CONCLUSION

The region of RALN undergoes rapid and dynamic changes in adhesion molecule expression during gestation, which may regulate interactions with intestine-associated immune cells shortly after birth.

Expression of the C. elegans labial orthologue ceh-13 during male tail morphogenesis

Hox genes are transcriptional regulators of metazoan body regionalization along the anteroposterior axis that act by specifying positional identity in differentiating cells. ceh-13, the labial orthologue in Caenorhabditis elegans, is expressed both during embryogenesis and post- embryonic development. Using GFP reporter analysis and immunocytochemistry, we discovered a spatiotemporal pattern of gene expression in the male tail during the L3 and L4 larval stages that is TGF-beta pathway-dependent. Analysis of reporter activity in transgenic animals identified a distinct promoter region driving male tail-specific ceh-13 expression. We also report the interspecies conservation of sequence motifs within this region and speculate that, in the course of evolutionary diversification, ceh-13 may have acquired new functionality while conserving its homeotic role.

Three-dimensional image reconstruction of an anorectal malformation with multidetector-row helical computed tomography technology

The presentation of the surgical anatomy of anorectal malformation by standard anatomical figures is not suitable for individual anorectoplasty. It is essential to understand the anatomy of the pelvic muscle (striated muscle complex: SMC) including the external anal sphincter and their three-dimensional (3D) configuration in each patient. Thus, we studied the SMC three-dimensionally with multidetector-row helical computed tomography (MRH-CT) preoperatively, and evaluated its usefulness. Fourteen patients with anorectal malformations before anorectoplasty (types: high n=6, intermediate n=2, low n=6) and two patients without anorectal malformations as controls (total: male n=8, female n=8) were investigated. An image of pelvic region was prepared with a slice thickness of 0.5 mm and a reconstruction pitch of 0.5 mm. A 3D reconstruction on a conventional personal computer (PC) was made with a volume rendering method, and assisted by our own software. The SMC was analyzed with three modified modes of 3D reconstruction corresponding to the surrounding tissues. A length of the parasagittal muscle, and both the sagittal and transverse width of the vertical fibers in the SMC at the connection to the parasagittal muscle were measured on a 3D image and then compared among three different types and controls. To eliminate variations in age, a length index was used to allow comparison. The 3D configuration of the SMC was different in every case. The arranged image mode, which displayed the SMC and the pelvic bones simultaneously, enabled to use conventional knowledge in cysto-urethrography. The length of the parasagittal muscle was longest in the high type but the width of the vertical fibers was smallest. Anatomical figures of the SMC including the external anal sphincter were clearly demonstrated on a PC in every anorectal malformation by our program. A 3D reconstruction image provides positional information on the SMC for the body surface and pelvic bone at the same time. Both a 3D image and positional information with MRH-CT offers the surgeon a simulated operative profile of the SMC superior to CT or magnetic resonance imaging slices alone.

Sharing of the same embryogenic pathway in anorectal malformations and anterior sacral myelomeningocele formation

The objective of this study was to determine whether anorectal malformations (ARMs) and anterior sacral myelomeningocele share the same embryogenic pathway in a mouse model. Etretinate (Ro 10-9359) was administrated to C57BL/6 mice on gestation day 9 (E9). Sections of embryos and fetuses from E9.5 to E18 were observed by HE staining. Immunohistochemical staining with anti-NeuN and anti-GFAP was also done to determine cell origins of a presacral mass. In etretinate-treated embryos, neuroepithelial cells proliferated in the presacral region on E9.5. On E12, a canal appeared between the ectopic proliferated neuroepithelium and hindgut. On E13, anorectum abnormally kept a canal with the ventral urogenital tract through a fistula. On E13.5, a huge mass formed in the presacral region. On E18, 76.9% (30/39) of fetuses had ARMs, 100% (39/39) had a presacral mass (71.8% were huge) and 100% (39/39) had a sacral defect. The types of ARMs were mainly rectourethral or rectocloacal fistula. The presacral mass was anterior sacral myelomeningocele. We thus established the first mouse model of the Currarino triad, congenital caudal anomalies, including ARM, sacral abnormality and presacral mass. These disorders share the same embryogenic pathway. The teratogenic target of etretinate is the tail bud. Abnormal differentiation of the tail bud mesenchyme leads to defects of the tailgut and caudal neural tube. The abnormal mass blocks normal descent of the dorsal cloaca through the most posterior part of the cloacal plate.

Fetal surgery for repair of myelomeningocele allows normal development of the rectum in sheep

To determine whether fetal surgery in a fetus with myelomeningocele (MMC) allows normal development of rectal muscles and nerves, we analyzed the rectum after fetal surgery in a sheep model. An MMC lesion was surgically created in 13 fetal sheep at 75 days of gestation. One fetal sheep died after the lesion was created. Eight fetal sheep were repaired at 100 days of gestation; the others were not repaired, as a control (n=4). Three methods were used for fetal surgery of MMC: standard neurosurgical repair (4 fetal sheep), covering of the MMC lesion by Alloderm (2 fetal sheep), and covering of the MMC lesion by Gore-Tex (2 fetal sheep). At 140 days of gestation, fetal sheep were harvested and histo-pathological analysis was performed on the rectum using hematoxylin and eosin staining for muscles and S-100 protein staining for nerves. One fetal sheep treated by standard neurosurgical repair died before harvesting. The four untreated fetal sheep had hypoplastic longitudinal muscles of the rectum but well developed-circular muscles. In addition, the untreated fetuses had a hypoplastic submucosal nerve plexus but a well-developed intermuscular nerve plexus. In contrast, treated fetal sheep had well-developed longitudinal and circular muscles except for one sheep treated with standard neurosurgical repair. In addition, except for the same fetal sheep, treated fetal sheep had well-developed nerve plexuses. There was no difference in muscle and nerve development of the rectum among the three repair methods. Fetal surgery for repair of MMC allows normal development of rectal muscles and nerves.

In-utero development of the fetal colon and rectum: sonographic evaluation

OBJECTIVE

To construct a normal range for the internal diameter of the fetal descending colon and rectum during gestation.

SUBJECTS AND METHODS

This was a prospective, cross-sectional study including 379 healthy pregnant women with normal singleton pregnancies at 19-40 weeks of gestation. Measurements of the fetal descending colon (maximum internal diameter) and the fetal rectum (at the level of the bladder, measuring the anteroposterior diameter), were performed by high-resolution transabdominal sonography.

RESULTS

Adequate bowel measurements were obtained in all 379 fetuses. The diameter of the descending colon and rectum plotted as a function of gestational age had a sigmoid curve; the curve estimation was expressed by a cubic regression equation with R(2) of 0.848 and 0.831, respectively (P < 0.0001). The normal mean and the 95% prediction limits were defined.

CONCLUSION

The present data provide a normal range of fetal bowel (descending colon and rectum) diameters from the early second trimester of pregnancy onwards. They may allow intrauterine assessment of the development of the fetal colon and may serve as reference values in the detection of anomalies of the fetal bowel.

Relationship of the fistulas to the rectum and genitourinary tract in mouse fetuses with high anorectal malformations induced by all-trans retinoic acid

Since high anorectal malformations with fistulae in human embryos and fetuses of successive developmental stages have not been reported, the embryologic relationship between the rectal fistula (RF) and the genitourinary tract (GUT) in high anorectal agenesis (ARA) remains to be elucidated. This study investigates the developmental relationship between the RF and the GUT in male and female fetuses with high ARA using our established model for high ARA with fistula in mice. Pregnant mice received all-trans retinoic acid suspended in corn oil (5 mg/ml) 100 mg/kg i.p. on day 9 of pregnancy. All fetuses were removed from the uterus on a single day from days 12 to 18 of pregnancy. The caudal regions were analyzed histologically with hematoxylin and eosin staining. All fetuses examined had high ARA with fistula. On day 12 of pregnancy, an anomalous communication was seen between the urogenital sinus (UGS) and the rectum. In the affected female fetuses, on day 14 of pregnancy the paramesonephric (müllerian) ducts and müllerian tubercle were located above the rectocloacal fistula (RCF), and on day 18 of pregnancy the uterovaginal canal was located between the cloaca and the RCF. In the male fetuses, on day 14 of pregnancy the junction between the mesonephric (wolffian) duct and the UGS was located away from the junction between the rectum and the UGS. On day 18 of pregnancy the ejaculatory duct was located between the urinary bladder and the rectourethral fistula. The results of our experiment clearly show the embryologic relationship between the RF and the GUT with high ARA. The anomalous communication between the UGS and the rectum may interfere with normal caudal migration along the dorsal wall of the UGS at the junction between the UGS and the mesonephric or paramesonephric duct.

Septation of the anorectal and genitourinary tracts in the human embryo: crucial role of the catenoidal shape of the urorectal sulcus

BACKGROUND

Previous studies of the tracheoesophageal sulcus and the sulci of the developing heart have suggested that the catenoidal or saddle-shaped configuration of the sulcus had mechanical properties that were important to developmental processes by causing regional growth limitation. We examined the development of the human perineal region to determine if a similar configuration exists in relation to the urorectal septum. We wished to re-examine the controversial issue of the role of the urorectal sulcus in the partitioning of the cloaca.

METHODS

Digitally scanned photomicrographs of serial histologic sections of embryos from Carnegie stages 13, 15, 18, and 22, obtained from the Carnegie Embryological Collection were used. Each image was digitally stacked, aligned, and isolated using image-editing software. Images were compiled using 3-D image-visualization software (T-Vox), into full 3-D voxel-based volume renderings. Similarly, digital models were made of the urogenital sinus, anorectum, cloaca, allantois, mesonephric ducts, ureters, and kidneys by isolating their associated epithelium in each histologic section and compiling the data in T-Vox. Methods were developed to create registration models for determining the exact position and orientation of outlined structures within the embryos.

RESULTS

Models were oriented and resectioned to determine the configuration of the urorectal sulcus. The results show that the urorectal sulcus maintains a catenoidal configuration during the developmental period studied and, thus, would be expected to limit caudal growth of the urorectal septum.

CONCLUSION

The observations support the concept that the urorectal septum is a passive structure that does not actively divide the cloaca into urogenital and anorectal components.

Location of stem cells for the enteric nervous system

Hirschsprung disease is the result of aganglionosis of a variable length of the terminal bowel, which arises from the incomplete colonisation of the embryonic gut by vagal neural crest-derived cells (NCC) that migrate caudally from the pharyngeal gut to the rectum. We have previously shown that a very small group of NCC, at the leading edge of this wave of migration, can proliferate and differentiate to innervate the entire distal gut. It remains unknown if this capability is unique to those cells at the leading edge of NCC migration. The hypothesis tested was that NCC capable of acting as stem cells are found throughout the developing enteric nervous system (ENS). Gut was taken from mice at embryonic day 11.5 as the leading edge of NCC migration enters the colon. Terminal colon was separated as aganglionic recipient gut and its rostral end juxtaposed to the caudal end of the small intestine or caecum. The explants were cultured on nitrocellulose filters for up to 120 h, after which time the apposed segments had fused. The gut was then fixed and examined by immunohistochemistry to detect the neuronal markers PGP9.5 and nitric-oxide synthase (NOS) to assess development of enteric ganglia. NCC migrated from the proximal gut into the terminal colon, colonising it along its entire length. The pattern of NCC colonisation and differentiation of NOS-positive neurons was the same, regardless of whether the NCC were derived from the leading edge of migration in the caecum or from more proximal regions of the small intestine. Vagal NCC have the capacity to migrate into separated aganglionic terminal colon and differentiate into neurons. NCC at the leading edge of migration and those located more proximally within the gut demonstrate equivalent ability to migrate to and differentiate in the terminal rectum. Further studies are required to confirm which of these migrating NCC have the properties of ENS stem cells.

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.

Magnetic resonance imaging in children with anorectal malformations: embryologic implications

PURPOSE

The aim of this study was to evaluate the spectrum of developmental anomalies in the caudal region of patients with anorectal malformations (ARM) and relate them to the new insights in the embryogenesis of this region.

METHODS

Forty-nine patients with ARM were investigated with magnetic resonance imaging (MRI); 24 preoperatively (preop) and 25 postoperatively (postop). Of this group, 17 patients had a high (or intermediate) ARM, 28 a low ARM, and 4 a cloacal malformation (CM). The evaluation of the imaging studies included the level and type of ARM (preop); the developmental state of the sphincter muscle complex (SMC); and the associated anomalies of spinal cord, spine, and urogenital system. The anomalies detected were ordered and related to recent embryologic observations in the caudal region.

RESULTS

With MRI, the level of ARM was depicted effectively in 23 of 24 patients (96%) investigated preop, including 5 of 9 clinically proven fistulae in those with high ARM and CM (56%). Maldevelopment of the SMC was observed in 14 of 49 patients (29%). Associated anomalies of spinal cord and spine were found in 51% of patients, more frequently in those with high ARM, low ARM with fistulae, and cloacal malformations. Associated anomalies of the urogenital system were found in 37% of patients.

CONCLUSIONS

As illustrated by the current study, MRI has become indispensable for the visualization of the nature of congenital ARM and associated anomalies. Moreover, MRI aids in understanding the morphology and pathogenesis of these complex congenital malformations. Based on the MRI and recent embryologic observations, a new and simplified classification of ARM is introduced, including a more appropriate nomenclature.

Three-dimensional reconstruction of the anorectal continence organ in a 14-week-old fetus

BACKGROUND/PURPOSE

The fetal development and anatomy of the muscular structures of the anorectal continence system are unclear. To the pediatric surgeon, these structures are of clinical relevance in reconstructive surgery. The aim of this study was to investigate the fetal development of the anorectal continence organ.

METHODS

A male fetus (14 weeks postconceptionem) of 114-mm crown-rump length was sectioned serially at 18-micrometer intervals. The sections were stained, and relevant contours of the sections were transferred onto paper using a Zeiss Axioskop drawing apparatus. The drawings then were scanned and digitized.

RESULTS

Three-dimensional images were created (and animated in a video). These have permitted the demonstration of isolated anatomic structures, the disassembling and reassembling of compound structures, as well as the visualization of structures from different angles.

CONCLUSIONS

Further studies are now undertaken of older fetal stages through to birth, as well as during postnatal stages. Comparative studies in animals and animations of isolated muscles also are required to show functional capacities. Such studies may lead eventually to an improvement of contemporary surgical techniques.

A Delta-Notch signaling border regulated by Engrailed/Invected repression specifies boundary cells in the Drosophila hindgut

The Drosophila hindgut develops three morphologically distinct regions along its anteroposterior axis: small intestine, large intestine and rectum. Single-cell rings of 'boundary cells' delimit the large intestine from the small intestine at the anterior, and the rectum at the posterior. The large intestine also forms distinct dorsal and ventral regions; these are separated by two single-cell rows of boundary cells. Boundary cells are distinguished by their elongated morphology, high level of both apical and cytoplasmic Crb protein, and gene expression program. During embryogenesis, the boundary cell rows arise at the juxtaposition of a domain of Engrailed (En)- plus Invected (Inv)-expressing cells with a domain of Delta (Dl)-expressing cells. Analysis of loss-of-function and ectopic expression phenotypes shows that the domain of Dl-expressing cells is defined by En/Inv repression. Further, Notch pathway signaling, specifically the juxtaposition of Dl-expressing and Dl-non-expressing cells, is required to specify the rows of boundary cells. This Notch-induced cell specification is distinguished by the fact that it does not appear to utilize the ligand Serrate and the modulator Fringe.

The cloacal plate: the missing link in anorectal and urogenital development

OBJECTIVE

To determine whether differences in the embryology of the anorectal and urogenital area, previously examined in sheep, pigs, rats, rabbits and guinea pigs, producing varying conclusions, may be secondary to differences in species development.

MATERIALS AND METHODS

Rat and human embryos were studied at the time of genital tubercle development and cloacal partition by standard serial-section histology, and by immunohistochemistry, dissection and scanning electron microscopy. The images obtained were compared with those previously reported for pig and sheep embryos.

RESULTS

The cloacal plate, a vertically orientated midline plate of epithelial cells in the caudal half of the genital tubercle, was the key structure that varied between the different species. In rats the plate maintained a vertical height along its length, while in humans and pigs it reverted to a two-layer membrane dorsally, shortly before it degenerated to expose both the anorectal and urogenital tracts. In sheep the plate was taller ventrally than in the other species but also reverted to a short membrane dorsally that exposed the hindgut when it degenerated. The anterior part of the cloacal plate persisted in all embryos as the urethral plate, which then participated in the formation of the urethra in the male and the vestibule in the female. The animal that most closely resembled humans in anogenital development was the pig.

CONCLUSIONS

The cloacal plate is the key to understanding early anorectal and urogenital development and yet it is barely recognized in published reports. An appreciation of its relevance helps to explain the variations in the described embryology of the region, and is mandatory when interpreting embryological findings in animal models of human anomalies. Given the similarities between porcine and human development, the pig may be the most legitimate animal model for the study of anorectal and urogenital anomalies in humans.

Rectovaginal fascia: An important structure in pelvic visceral surgery? About its development, structure, and function

BACKGROUND

The existence, development, and function of the rectovaginal fascia has been discussed in literature. In women, a defect in the fascia leads to rectoceles and severe constipation. In pediatric textbooks for anorectal or urogenital surgery, however, it is not mentioned. Does the fascia exist in children?

METHODS

The pelvises of 31 female and, as controls, 31 male fetuses (age from 9 weeks of gestation to newborn) were plastinated. Sections (transversal, sagittal, and frontal) were stained with azure II/ methylenblue/ basic fuchsin and viewed at a magnification of 6.5x to 80x. In addition, the authors investigated macroscopically and microscopically the rectovaginal fascia in 1 fetal and 1 adult cadaver.

RESULTS

At the beginning of the fetal period the authors recognized the anlage of the rectovaginal fascia caudal from the rectouterine excavation. Later, a fascia of connective tissue develops. It is connected directly to areolar connective tissue at the dorsal wall of the vagina. Neurovascular bundles are situated ventrolaterally of the rectal wall. At the level of the anorectal flexure this fascia separates the rectum and the vagina.

CONCLUSIONS

Our investigations indicate that the rectovaginal fascia is completely developed in newborns, through differentiation of mesenchyme, which develops into a fascia. It protects different compartments and serves as an abutment to the rectal wall. Thus, it is important for adequate bowel emptying. For the surgeon it is a leading structure for preventing nerve damage of the autonomic nerve supply of the pelvic organs. It should be known, protected, and, if necessary, reconstructed.