Neuronal dysplasia: A controversial pathological correlate of intestinal pseudo-obstruction

Enteric Nervous System Striped Patterning and Disease: Unexplored Pathophysiology

The enteric nervous system (ENS) controls gastrointestinal (GI) motility, and defects in ENS development underlie pediatric GI motility disorders. In disorders such as Hirschsprung's disease (HSCR), pediatric intestinal pseudo-obstruction (PIPO), and intestinal neuronal dysplasia type B (INDB), ENS structure is altered with noted decreased neuronal density in HSCR and reports of increased neuronal density in PIPO and INDB. The developmental origin of these structural deficits is not fully understood. Here, we review the current understanding of ENS development and pediatric GI motility disorders incorporating new data on ENS structure. In particular, emerging evidence demonstrates that enteric neurons are patterned into circumferential stripes along the longitudinal axis of the intestine during mouse and human development. This novel understanding of ENS structure proposes new questions about the pathophysiology of pediatric GI motility disorders. If the ENS is organized into stripes, could the observed changes in enteric neuron density in HSCR, PIPO, and INDB represent differences in the distribution of enteric neuronal stripes? We review mechanisms of striped patterning from other biological systems and propose how defects in striped ENS patterning could explain structural deficits observed in pediatric GI motility disorders.

Recurrent arginine substitutions in the ACTG2 gene are the primary driver of disease burden and severity in visceral myopathy

Visceral myopathy with abnormal intestinal and bladder peristalsis includes a clinical spectrum with megacystis-microcolon intestinal hypoperistalsis syndrome and chronic intestinal pseudo-obstruction. The vast majority of cases are caused by dominant variants in ACTG2; however, the overall genetic architecture of visceral myopathy has not been well-characterized. We ascertained 53 families, with visceral myopathy based on megacystis, functional bladder/gastrointestinal obstruction, or microcolon. A combination of targeted ACTG2 sequencing and exome sequencing was used. We report a molecular diagnostic rate of 64% (34/53), of which 97% (33/34) is attributed to ACTG2. Strikingly, missense mutations in five conserved arginine residues involving CpG dinucleotides accounted for 49% (26/53) of disease in the cohort. As a group, the ACTG2-negative cases had a more favorable clinical outcome and more restricted disease. Within the ACTG2-positive group, poor outcomes (characterized by total parenteral nutrition dependence, death, or transplantation) were invariably due to one of the arginine missense alleles. Analysis of specific residues suggests a severity spectrum of p.Arg178>p.Arg257>p.Arg40 along with other less-frequently reported sites p.Arg63 and p.Arg211. These results provide genotype-phenotype correlation for ACTG2-related disease and demonstrate the importance of arginine missense changes in visceral myopathy.

Peripheral nerve disease secondary to systemic conditions in children

This review is an overview of systemic conditions that can be associated with peripheral nervous system dysfunction. Children may present with neuropathic symptoms for which, unless considered, a causative systemic condition may not be recognized. Similarly, some systemic conditions may be complicated by comorbid peripheral neuropathies, surveillance for which is indicated. The systemic conditions addressed in this review are critical illness polyneuropathy, chronic renal failure, endocrine disorders such as insulin-dependent diabetes mellitus and multiple endocrine neoplasia type 2b, vitamin deficiency states, malignancies and reticuloses, sickle cell disease, neurofibromatosis, connective tissue disorders, bowel dysmotility and enteropathy, and sarcoidosis. In some disorders presymptomatic screening should be undertaken, while in others there is no benefit from early detection of neuropathy. In children with idiopathic peripheral neuropathies, systemic disorders such as celiac disease should be actively excluded. While management is predominantly focused on symptomatic care through pain control and rehabilitation, some neuropathies improve with effective control of the underlying etiology and in a small proportion a more targeted approach is possible. In conclusion, peripheral neuropathies can be associated with a diverse range of medical conditions and unless actively considered may not be recognized and inadequately managed.

Intestinal Neuronal Dysplasia Type B: An Updated Review of a Problematic Diagnosis

Context.—

Intestinal neuronal dysplasia type B (IND B) is a controversial histopathologic phenotype that has been associated with intestinal dysmotility, either as an isolated condition or in conjunction with established pathologic disorders (eg, Hirschsprung disease). Many factors contribute to the debate over the existence and/or clinical significance of IND B, including a large body of published data based on inconsistent diagnostic criteria and methods, which have fostered many unwarranted conclusions that lack sufficient scientific basis.

Objective.—

To critically analyze existing published data regarding IND B to provide supporting evidence-based diagnostic practice and to stimulate necessary and scientifically sound research.

Data Sources.—

This update focuses on published literature related to the pathology of IND B because without a reliable pathologic diagnosis, studies of epidemiology, pathogenesis, natural history, management, and outcome are all suspect. Problems with existing data are identified explicitly with suggestions as to how future investigations should be designed and evaluated to better understand this entity.

Conclusions.—

Inconsistencies in diagnostic criteria and methods used to define IND B justifiably encumber the universal acceptance of IND B as a neuropathologic etiology for intestinal dysmotility. IND B will remain a controversial diagnosis until rigorous, well-controlled scientific studies are conducted to establish reproducible and reliable diagnostic criteria that reliably translate from one laboratory to another.

Clinical aspects of neurointestinal disease: Pathophysiology, diagnosis, and treatment

The enteric nervous system (ENS) is involved in the regulation of virtually all gut functions. Conditions referred to as enteric neuropathies are the result of various mechanisms including abnormal development, degeneration or loss of enteric neurons that affect the structure and functional integrity of the ENS. In the past decade, clinical and molecular research has led to important conceptual advances in our knowledge of the pathogenetic mechanisms of these disorders. In this review we consider ENS disorders from a clinical perspective and highlight the advancing knowledge regarding their pathophysiology. We also review current therapies for these diseases and present potential novel reparative approaches for their treatment.

Neural stem cell therapies for enteric nervous system disorders

The enteric nervous system is vulnerable to a range of congenital and acquired disorders that disrupt the function of its neurons or lead to their loss. The resulting enteric neuropathies are some of the most challenging clinical conditions to manage. Neural stem cells offer the prospect of a cure given their potential ability to replenish missing or dysfunctional neurons. This article discusses diseases that might be targets for stem cell therapies and the barriers that could limit treatment application. We explore various sources of stem cells and the proof of concept for their use. The critical steps that remain to be addressed before these therapies can be used in patients are also discussed. Key milestones include the harvesting of neural stem cells from the human gut and the latest in vivo transplantation studies in animals. The tremendous progress in the field has brought experimental studies exploring the potential of stem cell therapies for the management of enteric neuropathies to the cusp of clinical application.

A practical guide for the diagnosis of primary enteric nervous system disorders

OBJECTIVE

Primary gastrointestinal neuropathies are a heterogeneous group of enteric nervous system (ENS) disorders that continue to cause difficulties in diagnosis and histological interpretation. Recently, an international working group published guidelines for histological techniques and reporting, along with a classification of gastrointestinal neuromuscular pathology. The aim of this article was to review and summarize the key issues for pediatric gastroenterologists on the diagnostic workup of congenital ENS disorders. In addition, we provide further commentary on the continuing controversies in the field.

RESULTS

Although the diagnostic criteria for Hirschsprung disease are well established, those for other forms of dysganglionosis remain ill-defined. Appropriate tissue sampling, handling, and expert interpretation are crucial to maximize diagnostic accuracy and reduce interobserver variability. The absence of validated age-related normal values for neuronal density, along with the lack of correlation between clinical and histological findings, result in significant diagnostic uncertainties while diagnosing quantitative aberrations such as hypoganglionosis or ultrashort Hirschsprung disease. Intestinal neuronal dysplasia remains a histological description of unclear significance.

CONCLUSIONS

The evaluation of cellular quantitative or qualitative abnormalities of the ENS for clinical diagnosis remains complex. Such analysis should be carried out in laboratories that have the necessary expertise and access to their own validated reference values.

Classification and diagnostic criteria of variants of Hirschsprung's disease

"Variants of Hirschsprung's disease" are conditions that clinically resemble Hirschsprung's disease (HD), despite the presence of ganglion cells in rectal suction biopsies. The diagnosis and management of these patients can be challenging. Specific histological, immunohistochemical and electron microscopic investigations are required to characterize this heterogeneous group of functional bowel disorders. Variants of HD include intestinal neuronal dysplasia, intestinal ganglioneuromatosis, isolated hypoganglionosis, immature ganglia, absence of the argyrophil plexus, internal anal sphincter achalasia and congenital smooth muscle cell disorders such as megacystis microcolon intestinal hypoperistalsis syndrome. This review article systematically classifies variants of HD based on current diagnostic criteria with an additional focus on pathogenesis, epidemiology, clinical presentation, management and outcome.

Histopathologic delineation of the transition zone in short-segment Hirschsprung disease

Failure to completely resect the transition zone (TZ) between aganglionic and neuroanatomically normal bowel ("TZ pull-through") is considered one reason for postoperative obstructive symptoms in Hirschsprung disease (HD). Despite years of study, the proximal boundary of the TZ remains nebulous, complicated by discordant, often subjective, histopathologic definitions. In order to objectively delineate the TZ, transverse sections at 1 cm intervals from the rectums of 9 non-HD autopsy subjects and resections from 15 infants with short-segment HD were immunostained with Hu (ganglion cell bodies) and glucose transporter 1 (Glut1) (perineurium of extrinsic nerves), and 6 putative features of TZ were examined: (1) aganglionosis of ≥1/8th circumference; (2) myenteric or submucosal hypoganglionosis; (3) hypertrophic submucosal nerves; (4) Glut1+ submucosal innervation; (5) submucosal hyperganglionosis; and (6) "ectopic" ganglia in lamina propria, muscularis propria, or serosa. In non-HD controls, Glut1+ submucosal innervation, hypertrophic nerves, partial circumferential aganglionosis, and hypoganglionosis were absent or restricted to the distal 2 cm. In contrast, all 6 neuropathologic features of TZ were identified proximal to the aganglionic segment in the majority of HD resections, but the length of the TZ ranged from 0 to 12 cm, depending on which neuropathologic feature was considered. Excluding submucosal hyperganglionosis and ectopic ganglia, the TZ was generally ≤5 cm. Many features of TZ cannot be excluded intraoperatively with a biopsy or a full-circumference frozen section. However, partial circumferential aganglionosis, severe myenteric hypoganglionosis, and hypertrophic submucosal nerves can, and probably should, be assessed in full-circumference frozen sections of the proximal resection margin, to reduce the likelihood of TZ pull-through.

A new diagnostic scoring system to differentiate Hirschsprung's disease from Hirschsprung's disease-allied disorders in patients with suspected intestinal dysganglionosis

PURPOSE

To create a simple diagnostic scoring system to differentiate Hirschsprung's disease (HD) from Hirschsprung's disease-allied disorders (HAD) in patients with suspected intestinal dysganglionosis (IDs).

METHODS

Between 1998 and 2008, 967 patients with suspected intestinal dysganglionosis underwent surgical treatment at the pediatric surgery department of Tongji Hospital. The diagnosis of HD or HAD was confirmed by postoperative pathological examination. All patients underwent preoperative work-up including barium enema, anorectal manometry, and histochemical acetylcholinesterase staining of rectal mucosa. Known risk factors for IDs were recorded. The predicting score was calculated by summing the scores of the risk factors and three preoperative tests. The sensitivity, specificity, accuracy, positive predictive values, negative predictive values, positive likelihood ratios, and negative likelihood ratios of the predicting score were calculated. The cutoff score for predicting HD was determined using receiver operating characteristic (ROC) analysis. The accuracy of the predicting score was measured by the area under the ROC curve.

RESULTS

Failed or delayed passage of meconium, age <3 years and male gender were risk factors associated with HD. The area under the ROC curve of the predicting score was 0.927 (95 % confidence interval, 0.910-0.944). A predicting score of more than 5 was used as a cutoff for predicting HD. The scoring system achieved 83.1 % sensitivity, 89.5 % specificity, and 85.9 % accuracy in predicting HD.

CONCLUSION

Patients with a predicting score of more than 5 are more likely to be diagnosed with HD, whereas a score less than 5 are mostly indicative of HAD.

Development and developmental disorders of the enteric nervous system

The enteric nervous system (ENS) arises from neural crest-derived cells that migrate into and along the gut, leading to the formation of a complex network of neurons and glial cells that regulates motility, secretion and blood flow. This Review summarizes the progress made in the past 5 years in our understanding of ENS development, including the migratory pathways of neural crest-derived cells as they colonize the gut. The importance of interactions between neural crest-derived cells, between signalling pathways and between developmental processes (such as proliferation and migration) in ensuring the correct development of the ENS is also presented. The signalling pathways involved in ENS development that were determined using animal models are also described, as is the evidence for the involvement of the genes encoding these molecules in Hirschsprung disease-the best characterized paediatric enteric neuropathy. Finally, the aetiology and treatment of Hirschsprung disease in the clinic and the potential involvement of defects in ENS development in other paediatric motility disorders are outlined.

Transitional zone pull through: surgical pathology considerations

Incomplete resection of the transitional zone (TZ) between histologically normal and aganglionic bowel in Hirschsprung disease is a putative cause of postoperative dysmotility. A review of literature indicates that diverse histopathological indexes have been used to define the TZ, and validated and reproducible diagnostic criteria have not been established. As a consequence, the proximal margin of the TZ is difficult to delimit, and the length of the TZ in a given patient depends on the diagnostic criteria used. Seromuscular biopsies are inadequate to exclude TZ, as diagnostic indexes may involve only a portion of the bowel circumference or the submucosa. Most published investigations of postoperative outcome after a TZ pull through (TZPT) conclude that the latter can cause persistent obstructive symptoms, which necessitate reoperation. However, the results of these studies are difficult to translate into clinical practice because most lack appropriate controls, and the overwhelming majority provide inadequate histopathological descriptions for reference at the time of intraoperative frozen section analysis. At present, a conservative approach based on frozen section examination of the entire proximal margin of the resection to exclude obvious subcircumferential aganglionosis (contiguous gap between ganglia of more than one-eighth of the circumference), hypoganglionosis (continuous string of myenteric ganglia comprised of 1 or 2 ganglion cells without surrounding neuropil), or hypertrophic submucosal nerves (>2 nerves with widths ≥40 μm per high-power field) seems prudent. Well-controlled studies to correlate proximal margin histology, especially subtle anatomic or immunohistochemical changes, with postoperative outcome are needed.

Morphological alterations of the enteric nervous system in young male patients with rectal prolapse

OBJECTIVES

The pathogenesis of rectal prolapse (RP) defined by a circumferential, full-thickness invagination of the rectal wall into the anal canal is controversial. RP is normally encountered in elderly women and attributed to several etiological factors (e.g., advanced age, pudendal nerve injury, laxity of supporting ligaments). RP affecting young male patients is unlikely to be explained by these factors and may be due to a rectal motility disorder. Therefore, the enteric nervous system (ENS) as key regulator of intestinal motility was evaluated by a systematic morphometric analysis.

PATIENTS AND METHODS

Full-thickness rectosigmoid specimens obtained from young male patients with symptomatic RP (n = 5) and male controls (n = 15) were processed for conventional histology and immunohistochemistry using anti-HuC/D as pan-neuronal marker. Enteric ganglia, nerve and glial cells were quantified separately in the myenteric (MP) and submucosal plexus (SMP).

RESULTS

Compared to controls, patients with RP showed significantly (p < 0.05) increased mean ganglionic area both in MP and SMP, increased mean neuronal content of submucosal ganglia, and nearly threefold higher frequency of submucosal ganglia containing ≥7 neurons.

CONCLUSION

The morphometric analysis reveals distinct quantitative alterations of the ENS in young male patients with RP mainly characterized by submucosal hyperganglionosis similar to histopathological features described in intestinal neuronal dysplasia. The data give evidence that RP in this unusual subgroup is associated with morphological changes of enteric ganglia which may contribute to the development of RP and complement established etiological concepts.

A new experimental approach is required in the molecular analysis of intestinal neuronal dysplasia type B patients

Intestinal neuronal dysplasia type B (INDB) is characterized by the malformation of the parasympathetic submucous plexus of the gut. It is generally accepted that INDB has a genetic basis, and several genes produce an INDB-like phenotype in mice when disrupted, such as EDNRB. However, no mutations associated with this disease have been identified in several series analysed. In the present studu, we sought to determine whether the EDNRB/EDN3 signalling pathway plays a role in the pathogenesis of INDB in humans. Denaturing high performance liquid chromatography (dHPLC) techniques were employed to screen the EDNRB and EDN3 coding regions in 23 INDB patients. In addition, association studies were performed on these genes with single nucleotide polymorphisms strategically selected and genotyped by TaqMan technology. Although several novel variants were detected in both genes, none of these variants appeared to play a functional role in protein function or expression. Our results indicate that additional screening of other candidate genes in larger patient series is required to elucidate the molecular basis of INDB. Additionally, the systematic lack of positive results in the screening of candidate genes for INDB reported in the literature, together with our results, leads us to propose that INDB may alternatively arise as a consequence of gain of function mutations in genes related to enteric nervous system development. Therefore, the use of different molecular approaches, such as screening for genetic duplication or enhancer mutations, is recommended for future studies on the genetic basis of INDB.

Pathology of Intestinal Motor Disorders in Children

Varied intestinal neuromuscular pathologies are responsible for Hirschsprung disease and other forms of chronic pseudo-obstruction that are encountered in pediatrics. Pathologically distinct subtypes discussed in this review include aganglionosis, hypoganglionosis, neuronal intranuclear inclusion disease, ganglionitis, degenerative neuropathy, diffuse ganglioneuromatosis, neuronal dysplasia, malformations of the muscularis propria, degenerative leiomyopathy, leiomyositis, and mitochondriopathies. Emphasis is given to the histopathologic features that distinguish these conditions and their differential diagnoses.

Search for pathogenetic variants of the SPRY2 gene in intestinal innervation defects

SPRY2 is an inducible inhibitor of signalling mediated by tyrosine kinases receptors, whose targeting causes intestinal hyperganglionosis in mice. In this light, we have undertaken a mutational analysis of the SPRY2 gene in patients affected with intestinal neuronal dysplasia (IND), without detecting nucleotide changes in any of the 26 DNA samples analysed, with the exception of two already known polymorphic variants. A role of the SPRY2 gene in IND pathogenesis can be thus excluded.

Deletion of Pten in the mouse enteric nervous system induces ganglioneuromatosis and mimics intestinal pseudoobstruction

Intestinal ganglioneuromatosis is a benign proliferation of nerve ganglion cells, nerve fibers, and supporting cells of the enteric nervous system (ENS) that can result in abnormally large enteric neuronal cells (ENCs) in the myenteric plexus and chronic intestinal pseudoobstruction (CIPO). As phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a phosphatase that is critical for controlling cell growth, proliferation, and death, we investigated the role of PTEN in the ENS by generating mice with an embryonic, ENC-selective deletion within the Pten locus. Mutant mice died 2 to 3 weeks after birth, with clinical signs of CIPO and hyperplasia and hypertrophy of ENCs resulting from increased activity of the PI3K/PTEN-AKT-S6K signaling pathway. Further analysis revealed that PTEN was only expressed in developing mouse embryonic ENCs from E15.5 and that the rate of ENC proliferation decreased once PTEN was expressed. Specific deletion of the Pten gene in ENCs therefore induced hyperplasia and hypertrophy in the later stages of embryogenesis. This phenotype was reversed by administration of a pharmacological inhibitor of AKT. In some human ganglioneuromatosis forms of CIPO, PTEN expression was found to be abnormally low and S6 phosphorylation increased. Our study thus reveals that loss of PTEN disrupts development of the ENS and identifies the PI3K/PTEN-AKT-S6K signaling pathway as a potential therapeutic target for ganglioneuromatosis forms of CIPO.

Practical pathology and genetics of Hirschsprung's disease

Diagnosis and management of Hirschsprung's disease (HSCR) requires understanding of the malformation's anatomic features and multigenic nature. Rectal biopsies, intraoperative frozen sections, and resection specimens provide invaluable information. Extraction of these data requires thoughtful biopsy technique, adequate histologic sections, histochemistry, and collaboration of surgeon and pathologist. Critical consideration of transition zone anatomy and published studies of "transition zone pull through" indicate that more research is needed to determine how much ganglionic bowel should be resected from HSCR patients. Many HSCR-susceptibility genes have been identified, but mutational analysis has limited practical value unless family history or clinical findings suggest syndromic HSCR.

Gastrointestinal neuromuscular pathology: guidelines for histological techniques and reporting on behalf of the Gastro 2009 International Working Group

The term gastrointestinal neuromuscular disease describes a clinically heterogeneous group of disorders of children and adults in which symptoms are presumed or proven to arise as a result of neuromuscular, including interstitial cell of Cajal, dysfunction. Such disorders commonly have impaired motor activity, i.e. slowed or obstructed transit with radiological evidence of transient or persistent visceral dilatation. Whilst sensorimotor abnormalities have been demonstrated by a variety of methods in these conditions, standards for histopathological reporting remain relatively neglected. Significant differences in methodologies and expertise continue to confound the reliable delineation of normality and specificity of particular pathological changes for disease. Such issues require urgent clarification to standardize acquisition and handling of tissue specimens, interpretation of findings and make informed decisions on risk-benefit of full-thickness tissue biopsy of bowel or other diagnostic procedures. Such information will also allow increased certainty of diagnosis, facilitating factual discussion between patients and caregivers, as well as giving prognostic and therapeutic information. The following report, produced by an international working group, using established consensus methodology, presents proposed guidelines on histological techniques and reporting for adult and paediatric gastrointestinal neuromuscular pathology. The report addresses the main areas of histopathological practice as confronted by the pathologist, including suction rectal biopsy and full-thickness tissue obtained with diagnostic or therapeutic intent. For each, indications, safe acquisition of tissue, histological techniques, reporting and referral recommendations are presented.

Development of enteric neuron diversity

The mature enteric nervous system (ENS) is composed of many different neuron subtypes and enteric glia, which all arise from the neural crest. How this diversity is generated from neural crest-derived cells is a central question in neurogastroenterology, as defects in these processes are likely to underlie some paediatric motility disorders. Here we review the developmental appearance (the earliest age at which expression of specific markers can be localized) and birthdates (the age at which precursors exit the cell cycle) of different enteric neuron subtypes, and their projections to some targets. We then focus on what is known about the mechanisms underlying the generation of enteric neuron diversity and axon pathfinding. Finally, we review the development of the ENS in humans and the etiologies of a number of paediatric motility disorders.

Advantages of intraoperative semiquantitative evaluation of myenteric nervous plexuses in patients with Hirschsprung disease

BACKGROUND

The reappearance of an occlusive syndrome after surgical treatment of patients with Hirschsprung disease is often caused by incomplete resection of the affected segment. Intraoperative examination of frozen biopsies assists surgery, but interpretation of biopsies in the transitional zone is difficult.

METHODS

We performed retrospective semiquantitative evaluations of myenteric nervous plexuses at the proximal limits of resection specimens from 41 children who were treated for rectocolic Hirschsprung disease using intraoperative examination of transparietal biopsies. The results of the evaluations were correlated with the postoperative courses of the children.

RESULTS

After formalin fixation, the mean length of the aganglionic segments was 8.9 cm (range, 1-37.5 cm). At the proximal limit, the percentage of the circumference of the muscularis propria that was composed of plexuses with ganglion cells was more than 95% in 7 children, 90% to 95% in 21 children, 40% to 80% in 6 children, and 30% or less in 7 children (17%), 4 of whom subsequently developed occlusive syndromes.

CONCLUSIONS

Semiquantitative intraoperative examination of the entire circumference of resected segments facilitates precise evaluation of intrinsic innervation at the level of the anastomosis and may reduce the frequency of recurrence of occlusive symptoms after surgery.

Transcriptional regulation of TLX2 and impaired intestinal innervation: possible role of the PHOX2A and PHOX2B genes

TLX2 (also known as HOX11L1, Ncx and Enx) is a transcription factor playing a crucial role in the development of the enteric nervous system, as confirmed by mice models exhibiting intestinal hyperganglionosis and pseudo-obstruction. However, congenital defects of TLX2 have been excluded as a major cause of intestinal motility disorders in patients affected with intestinal neuronal dysplasia (IND) or pseudo-obstruction. After demonstrating the direct regulation of TLX2 expression by the homeoprotein PHOX2B, in the present work, we have focused on its paralogue PHOX2A. By co-transfections, electrophoretic mobility shift assays and chromatin immunoprecipitation, we have demonstrated that PHOX2A, like PHOX2B, is involved in the cascade leading to TLX2 transactivation and presumably in the intestinal neuronal differentiation. Based on the hypothesis that missed activation of the TLX2 gene induces the development of enteric nervous system defects, PHOX2A and PHOX2B have been regarded as novel candidate genes involved in IND and pseudo-obstruction and consequently analyzed for mutations in a specific set of 26 patients. We have identified one still unreported PHOX2A variant; however, absence of any functional effect on TLX2 transactivation suggests that regulators or effectors other than the PHOX2 genes must act in the same pathway, likely playing a non redundant and direct role in the pathogenesis of such enteric disorders.

Enteric nervous system and developmental abnormalities in childhood

ENS consists of a complex network of neurons, organised in several plexuses, which interact by means of numerous neurotransmitters. It is capable of modulating the intestinal motility, exocrine and endocrine secretions, microcirculation and immune and inflammatory responses within the gastrointestinal tract, independent of the central nervous system. Though the embryological development of various plexuses are completed by mid-way of gestation, the maturation of neurons and nerve plexuses appear to continue well after birth. Therefore, any histological or functional abnormalities related to the gastrointestinal function must be investigated with the ongoing maturational processes in mind.

Intestinal neuronal dysplasia type B: one giant ganglion is not good enough

In this "Current Practice in Pediatric Pathology" article, 2 experts in the field and an associate editor of Pediatric and Developmental Pathology discuss the definition, diagnosis, clinical significance, and management of intestinal neuronal dysplasia type B. Intestinal neuronal dysplasia type B has constituted a diagnostic challenge ever since its first description more than 30 years ago. Intestinal neuronal dysplasia type B is regarded by many as a subtle malformation of the enteric nervous system that is limited to the submucosal plexus of the colon. The precise etiology remains unknown, and, to date, no specific diagnostic test exists other than morphology. Over time, with increasing experience, obligate pathological features have been adapted and refined, leading to contemporary diagnostic criteria that are enunciated in this review and placed into context with prior published data. Rigorous application of these criteria, under standardized laboratory conditions, is crucial for accurate diagnosis and future advances in this field.

Developmental changes in submucosal nitrergic neurons in the porcine distal colon

BACKGROUND/PURPOSE

As our understanding of the enteric nervous system improves, it becomes clear that it is no longer sufficient to simply determine whether enteric ganglion cells are present but also to determine whether correct number and types of ganglion cells are present. Nitric oxide is recognized as a potent mediator of inhibitory nerves responsible for the relaxation of the smooth muscle of the gastrointestinal tract. The aim of this study was to determine the normal nitrergic neuronal density and morphology in the submucosal plexus of the porcine distal bowel from fetal life to adulthood.

METHODS

Distal large bowel specimens were obtained from porcine fetuses of gestational age E60 (n = 5), E90 (n = 5), 1-day-old piglets (n = 5), 4-week-old piglets (n = 5), 12-week-old piglets (n = 5), and adult pigs (n = 5). Whole-mount preparations of the submucosal plexus were made and stained with NADPH diaphorase histochemistry. The ganglia density, the number of ganglion cells per ganglia, and nucleus and cytoplasmic area were measured.

RESULTS

Ganglia density decreased progressively and markedly with age until the adulthood (P < .001). On the contrary, ganglion cells increased their size over time predominantly because of increase in cytoplasm (P < .001). The number of ganglion cells per ganglia increased significantly during the fetal life. However, there was a significant reduction in the number of ganglion cells per ganglia during the period from birth to 4 weeks, remaining constant thereafter (P < .001).

CONCLUSIONS

The quantitative and qualitative morphometric analysis of the colonic submucous plexus shows that significant developmental changes occur during fetal and postnatal life. These findings indicate that the age of the patient is of utmost importance during histopathologic evaluation of enteric nervous system disorders.

Hox11L1 expression by precursors of enteric smooth muscle: an alternative explanation for megacecum in HOX11L1-/- mice

Previous studies have focused on expression of Hox11L1 in enteric neurons as the explanation for intestinal and urinary bladder dysmotility observed in mice that do not have the transcription factor. However, Hox11L1 is also expressed transiently in endo-, meso-, and ectodermal cells of the most caudal embryo during gastrulation. We sought to more fully characterize the fates of these cells because they might help explain the pathogenesis of lethal pseudo-obstruction in Hox11L1-null mice. The Cre recombinase cDNA was introduced into the Hox11L1 locus, and expression of the "knock-in" allele was used to activate the Rosa26R, beta-galactosidase reporter gene in cells with ongoing Hox11L1 transcription and their descendants. During gastrulation, Rosa26R activation was observed in progenitors of caudal somatic and visceral cells, including enteric smooth muscle. Expression in enteric neural precursors appeared much later. Analysis of endogenous Hox11L1 mRNA in aneuronal segments of large intestine that were grafted under the renal capsule indicated that the early activation of Hox11L1 in visceral mesoderm was transient and ceased before colonization of the large intestine by neural progenitors. Mice homozygous for the Cre allele died shortly after weaning, with cecal and proximal colonic distention but without overt anatomic defects that might represent maldevelopment of the visceral mesoderm. Our findings expand the range of possible functions of Hox11L1 to include activation of an as yet unknown developmental program in visceral smooth muscle and allow the possibility that intestinal dysmotility in Hox11L1-null animals may not be a primary neural disorder.

Variant Hirschsprung's disease

Conditions that clinically resemble HD despite the presence of ganglion cells on suction rectal biopsy results, can be diagnosed by providing an adequate biopsy and employing a variety of histological techniques. Intestinal neuronal dysplasia is a distinct clinical entity that can be clearly proven histologically. Patients with IND not only have abnormalities of submucosal and myenteric plexuses but also defective innervation of the muscle. Internal sphincter achalasia, which is histologically characterized by nitrergic nerve depletion, can be diagnosed on anorectal manometry and successfully treated by internal sphincter myectomy. The outcome of smooth muscle disorders is generally fatal. The need for surgical intervention should be weighed carefully and individualized because most explorations have not been helpful and are probably not necessary.