Sexual dimorphism of the human fetal pelvis exists at the onset of primary ossification.

Human adolescent and adult skeletons exhibit sexual dimorphism in the pelvis. However, the degree of sexual dimorphism of the human pelvis during prenatal development remains unclear. Here, we performed high-resolution magnetic resonance imaging-assisted pelvimetry on 72 human fetuses (males [M]: females [F], 34:38; 21 sites) with crown-rump lengths (CRL) of 50-225 mm (the onset of primary ossification). We used multiple regression analysis to examine sexual dimorphism with CRL as a covariate. Females exhibit significantly smaller pelvic inlet anteroposterior diameters (least squares mean, [F] 8.4 mm vs. [M] 8.8 mm, P = 0.036), larger subpubic angle ([F] 68.1° vs. [M] 64.0°, P = 0.034), and larger distance between the ischial spines relative to the transverse diameters of the greater pelvis than males. Furthermore, the sacral measurements indicate significant sex-CRL interactions. Our study suggests that sexual dimorphism of the human fetal pelvis is already apparent at the onset of primary ossification.

Scientists isolate the genes that shape the human pelvis.

Embryonic tissue samples reveal how pelvis shape-primed for bipedalism-comes to life.

The developing bird pelvis passes through ancestral dinosaurian conditions.

Living birds (Aves) have bodies substantially modified from the ancestral reptilian condition. The avian pelvis in particular experienced major changes during the transition from early archosaurs to living birds1,2. This stepwise transformation is well documented by an excellent fossil record2-4; however, the ontogenetic alterations that underly it are less well understood. We used embryological imaging techniques to examine the morphogenesis of avian pelvic tissues in three dimensions, allowing direct comparison with the fossil record. Many ancestral dinosaurian features2 (for example, a forward-facing pubis, short ilium and pubic 'boot') are transiently present in the early morphogenesis of birds and arrive at their typical 'avian' form after transitioning through a prenatal developmental sequence that mirrors the phylogenetic sequence of character acquisition. We demonstrate quantitatively that avian pelvic ontogeny parallels the non-avian dinosaur-to-bird transition and provide evidence for phenotypic covariance within the pelvis that is conserved across Archosauria. The presence of ancestral states in avian embryos may stem from this conserved covariant relationship. In sum, our data provide evidence that the avian pelvis, whose early development has been little studied5-7, evolved through terminal addition-a mechanism8-10 whereby new apomorphic states are added to the end of a developmental sequence, resulting in expression8,11 of ancestral character states earlier in that sequence. The phenotypic integration we detected suggests a previously unrecognized mechanism for terminal addition and hints that retention of ancestral states in development is common during evolutionary transitions.

Feasibility of a fetal anatomy 3D atlas by computer-assisted anatomic dissection.

OBJECTIVE: To assess the feasibility of 3D modelisation of fetal anatomy by using the Computer-assisted anatomic dissection (CAAD) based on immunolabeled histologic slices and MRI slices with a specific 3D software. STUDY DESIGN: For pelvis and lower limbs, subjects came from legal abortion, medical pregnancy termination, or late miscarriage. Specimens were fixed in 10 % formalin, then embedded in paraffin wax and serially sectioned. The histological slices were stained using HES and Masson Trichrome. Protein S-100 and D2-40 markers were used for immuno-labelling. Serial transverse sections were digitalized and manually aligned. Fetal brain slices were obtained from in utero or post-mortem MRI. RESULTS: CAAD was performed on 10 fetuses: pelvis was modelised with 3 fetuses of 13, 15 and 24 W G, lower limbs with 2 fetuses of 14 and 15 W G and brain with 5 fetuses aged between 19 and 37 W G. Fetal pelvis innervation was analysed after immunolabelling and nerves appeared proportionally bigger than in adults with the same topography. Lower limbs analysis revealed that nerve development was guided by vascular development: the sciatic nerve along the big axial vein, the saphen nerve along the big saphen vein and the sural nerve along the small saphen vein. Fetal brain study allowed to describe the gyration process and the lateral ventricle development. CONCLUSION: CAAD technique provides an accurate 3D reconstruction of fetal anatomy for lower limbs and pelvis but has to be improved for brain model since midline structures were not amendable for analysis. These results need to be confirmed with larger series of specimens at different stages of development.

Size and shape correlation of birds' pelvis and egg: Impact of developmental mode, habitat, and phylogeny.

While eggs shapes and sizes have been subject of many studies, we still know little about factors affecting these characteristics of birds' eggs. We revealed that shapes of pelvis and egg correlated less than their respective sizes. Egg measurements (length or diameter) scaled with negative allometry against pelvis size, that is, eggs become relatively larger with decreasing pelvis size. Studied birds with altricial developmental mode had on average the smallest pelvic dimensions and the largest relative size of eggs. However, this is due to the effect of small pelvis size (and body as a whole) of most altricials. At the similar size of the pelvis, birds with altricial developmental mode had a smaller relative size of eggs than their precocial counterparts. Correlation between the shape of egg and pelvis is affected by habitat. Narrow pelvis with an elongated postacetabular region correlated with elongated eggs in diving waterfowl. In raptorial birds, the relatively wide pelvis with the shortened postacetabular region correlated with the nearly rounded shape of eggs.

Cartilage formation in the pelvic skeleton during the embryonic and early-fetal period.

The pelvic skeleton is formed via endochondral ossification. However, it is not known how the normal cartilage is formed before ossification occurs. Furthermore, the overall timeline of cartilage formation and the morphology of the cartilage in the pelvis are unclear. In this study, cartilage formation in the pelvic skeletons of 25 human fetuses (crown-rump length [CRL] = 11.9-75.0 mm) was observed using phase-contrast computed tomography and 7T magnetic resonance imaging. The chondrification center of the ilium, ischium, and pubis first appeared simultaneously at Carnegie stage (CS) 18, was located around the acetabulum, and grew radially in the later stage. The iliac crest formed at CS20 while the iliac body's central part remained chondrified. The iliac body formed a discoid at CS22. The growth rate was greater in the ilium than in the sacrum-coccyx, pubis, and ischium. Connection and articulation formed in a limited period, while the sacroiliac joint formed at CS21. The articulation of the pubic symphysis, connection of the articular column in the sacrum, and Y-shape connection of the three parts of the hip bones to the acetabulum were observed at CS23; the connection of the ischium and pubic ramus was observed at the early-fetal stage. Furthermore, the degree of connection at the center of the sacrum varied among samples. Most of the pelvimetry data showed a high correlation with CRL. The transverse and antero-posterior lengths of the pelvic inlet of the lesser pelvis varied among samples (R2 = 0.11). The subpubic angle also varied (65-90°) and was not correlated with CRL (R2 = 0.22). Moreover, cartilaginous structure formation appeared to influence bone structure. This study provides valuable information regarding the morphogenesis of the pelvic structure.

Ontogeny of the Human Pelvis.

The human pelvis has evolved over time into a remarkable structure, optimised into an intricate architecture that transfers the entire load of the upper body into the lower limbs, while also facilitating bipedal movement. The pelvic girdle is composed of two hip bones, os coxae, themselves each formed from the gradual fusion of the ischium, ilium and pubis bones. Unlike the development of the classical long bones, a complex timeline of events must occur in order for the pelvis to arise from the embryonic limb buds. An initial blastemal structure forms from the mesenchyme, with chondrification of this mass leading to the first recognisable elements of the pelvis. Primary ossification centres initiate in utero, followed post-natally by secondary ossification at a range of locations, with these processes not complete until adulthood. This cascade of events can vary between individuals, with recent evidence suggesting that fetal activity can affect the normal development of the pelvis. This review surveys the current literature on the ontogeny of the human pelvis. Anat Rec, 300:643-652, 2017. © 2017 Wiley Periodicals, Inc.

The sacral autonomic outflow is sympathetic.

A kinship between cranial and pelvic visceral nerves of vertebrates has been accepted for a century. Accordingly, sacral preganglionic neurons are considered parasympathetic, as are their targets in the pelvic ganglia that prominently control rectal, bladder, and genital functions. Here, we uncover 15 phenotypic and ontogenetic features that distinguish pre- and postganglionic neurons of the cranial parasympathetic outflow from those of the thoracolumbar sympathetic outflow in mice. By every single one, the sacral outflow is indistinguishable from the thoracolumbar outflow. Thus, the parasympathetic nervous system receives input from cranial nerves exclusively and the sympathetic nervous system from spinal nerves, thoracic to sacral inclusively. This simplified, bipartite architecture offers a new framework to understand pelvic neurophysiology as well as development and evolution of the autonomic nervous system.

Careful Dissection of the Distal Ureter Is Highly Important in Nerve-sparing Radical Pelvic Surgery: A 3D Reconstruction and Immunohistochemical Characterization of the Vesical Plexus.

OBJECTIVE: Radical hysterectomy with pelvic lymphadenectomy (RHL) is the preferred treatment for early-stage cervical cancer. Although oncological outcome is good with regard to recurrence and survival rates, it is well known that RHL might result in postoperative bladder impairments due to autonomic nerve disruption. The pelvic autonomic network has been extensively studied, but the anatomy of nerve fibers branching off the inferior hypogastric plexus to innervate the bladder is less known. Besides, the pathogenesis of bladder dysfunction after RHL is multifactorial but remains unclear. We studied the 3-dimensional anatomy and neuroanatomical composition of the vesical plexus and describe implications for RHL. MATERIALS AND METHODS: Six female adult cadaveric pelvises were macroscopically dissected. Additionally, a series of 10 female fetal pelvises (embryonic age, 10-22 weeks) was studied. Paraffin-embedded blocks were transversely sliced in 8-µm sections. (Immuno) histological analysis was performed with hematoxylin and eosin, azan, and antibodies against S-100 (Schwann cells), tyrosine hydroxylase (postganglionic sympathetic fibers), and vasoactive intestinal peptide (postganglionic parasympathetic fibers). The results were 3-dimensionally visualized. RESULTS: The vesical plexus formed a group of nerve fibers branching off the ventral part of the inferior hypogastric plexus to innervate the bladder. In all adult and fetal specimens, the vesical plexus was closely related to the distal ureter and located in both the superficial and deep layers of the vesicouterine ligament. Efferent nerve fibers belonging to the vesical plexus predominantly expressed tyrosine hydroxylase and little vasoactive intestinal peptide. CONCLUSIONS: The vesical plexus is located in both layers of the vesicouterine ligament and has a very close relationship with the distal ureter. Complete mobilization of the ureter in RHL might cause bladder dysfunction due to sympathetic and parasympathetic denervation. Hence, the distal ureter should be regarded as a risk zone in which the vesical plexus can be damaged.

Concepts of the rectovaginal septum: implications for function and surgery.

INTRODUCTION: In the pelvis, the rectogenital septum (RGS) separates the urogenital compartment from the digestive compartment. In men, it corresponds to Denonvilliers' rectoprostatic fascia or rectovesical septum (RVS). Its purpose-and, indeed, its existence-are controversial in women. The purpose of this review was to update knowledge about the RGS in women and, in particular, to clarify its relationship to pelvic nerves in order to deduce practical consequences of pelvic surgery and compare it to the RVS in men. METHODS: A review of the anatomical and surgical literature was undertaken. Evidence for embryological origin, composition, and surgical importance of the RGS in women and men is suggested. RESULTS: This manuscript presents evidence of the existence of the RGS in both women (rectovaginal septum, RVaS) and men (rectovesical septum, RVS). It originates from the genital structures and extends from the rectogenital pouch to the perineal body. It is composed of connective tissue associated with bundles of smooth muscle cells and has lateral expansions in close contact with neurovascular bundles originating from the inferior hypogastric plexus. During pelvic surgery for carcinoma, preservation of nerve fibers of erectile bodies is necessary if possible. The RGS is thus an important surgical landmark during urogenital sinus surgery, prolapse surgery, and proctectomy in women as well as during proctectomy and prostatectomy in men. CONCLUSIONS: The RGS is present in women as well as in men, with great similarities between the two sexes. It represents an important surgical landmark during pelvic nerve-sparing surgery.

Denonvilliers' fascia revisited.

Although several studies have reported that the peritoneum does not contribute to the formation of a fascia between the urogenital organs and rectum, Denonvilliers' fascia (DF), a fascia between the mesorectum and prostate (or vagina) in adults, is believed to be a remnant of the peritoneum. Remnants of the peritoneum, however, were reportedly difficult to detect in other fusion fasciae of the abdominopelvic region in mid-term fetuses. To examine morphological changes of the pelvic cul-de-sac of the peritoneum, we examined 18 male and 6 female embryos and fetuses. A typical cul-de-sac was observed only at 7 weeks, whereas, at later stages, the peritoneal cavity did not extend inferiorly to the level of the prostatic colliculus or the corresponding structure in females. The cul-de-sac had completely disappeared in front of the rectum at 8 weeks and homogeneous and loose mesenchymal tissue was present in front of the rectum at the level of the colliculus at 12-16 weeks. We found no evidence that linearly arranged mesenchymal cells developed into a definite fascia. Therefore, the development of the DF in later stages of fetal development may result from the mechanical stress on the increased volumes of the mesorectum, seminal vesicle, prostate and vagina and/or enlarged rectum. Therefore, we considered the DF as a tension-induced structure rather than a fusion fascia. Fasciae around the viscera seemed to be classified into (1) a fusion fascia, (2) a migration fascia and (3) a tension-induced fascia although the second and third types are likely to be overlapped.

Genetic analysis of the role of Alx4 in the coordination of lower body and external genitalia formation.

Although several syndromes include abnormalities of both the ventral body wall and external genitalia, the developmental bases of this correlation are largely unknown. Naturally occurring mutations in Aristaless-like 4 (Alx4, Strong's luxoid: Alx4Lst) have ventral body wall and pelvic girdle abnormalities. We sought to determine whether the development of the genital tubercle (GT) and its derivatives, the external genitalia, is affected by this mutation. We thus performed genetic and tissue labeling analyses in mutant mice. Alx4Lst/Lst mutants displayed hypoplasia of the dorsal GT and reduced expression of Fibronectin. We analyzed cell migration during GT formation by tissue labeling experiments and discovered that the cells located in the proximal segment of the umbilical cord (infra-umbilical mesenchyme) migrate toward the dorsal part of the GT. The Alx4Lst/Lst mutants also displayed augmented expression of Hh signal-related genes. Hence, we analyzed a series of combinatorial mutants for Alx4, Sonic hedgehog (Shh) and GLI-Kruppel family member 3 (Gli3). These phenotype-genotype analyses suggested a genetic interaction between Alx4 and Hh signaling during GT formation. Moreover, Hh gain-of-function mutants phenocopied some of these phenotypes. These observations reveal novel information regarding the pathogenic mechanisms of syndromic lower ventral body malformations, which are largely unknown.

Biomechanical origin of the Denonvilliers' fascia.

INTRODUCTION: Since 1836 and the first description of the recto-genital fascia by Charles Denonvilliers, many anatomists have shown interest in this subject. Recently, pelvic surgeons have in turn shown similar interest, for they consider that perfect knowledge of this anatomical domain is crucial for optimal nerve conservation during surgery. Thanks to new anatomical description techniques, fascia location and relationships with pelvic nerves now appear clearer. OBJECTIVES: To describe and represent Denonvilliers' fascia and its relationships in the female foetus at different stages of gestation and in three-dimensional space (3D). MATERIEL/PATIENTS AND METHODS: Computer-assisted anatomical dissection technique was used. Serial histological sections were made from four human female foetuses. Sections were treated with conventional staining, as well as with nerve and smooth muscle immunostaining. Finally, the sections were digitalized and reconstructed in 3D. RESULTS: Denonvilliers' fascia was clearly located and visualized in three dimensions. It was present in the female foetus, being distinct from the fascia propria of the rectum. It appeared to be composed of multiple parallel layers situated between the vagina and the rectum. From a lateral view, it had an asymmetrical "Y-shaped" aspect that seemed to play the role of a protective sheet for the neurovascular bundles. CONCLUSION: This study betters our comprehension of the Denonvilliers' fascia in the female foetus and of its connections with pelvic nerves. It also provides a better understanding of safe planes during pelvic dissection. These findings also suggest a biomechanical theory for embryological origin of the Denonvilliers' fascia.

Optimal plane for nerve sparing total mesorectal excision, immunohistological study and 3D reconstruction: an embryological study.

AIM: Genito-urinary complications are frequent after rectal surgery and are often due to nerve damage. The relationship between the pelvic nerves and surgical planes are unclear. The aim of the study was to determine the relationship between the inferior hypogastric plexus and the fascia of the lateral pelvic wall and between Denonvilliers' fascia and the efferent branches of the inferior hypogastric plexus. METHOD: Computer-assisted anatomical dissection was used. Serial histological sections were made from six human foetuses and a male adult. Sections were stained with haematoxylin and eosin, Masson's trichrome and immunostainings. The sections were then digitalized and reconstructed in three dimensions. RESULTS: The inferior hypogastric plexus was situated in a virtual space between the fascia propria of the rectum and the fascia on the upper surface of the levator ani. During the lateral dissection, the optimal surgical plane is the plane of the fascia propria of the rectum. We located Denonvilliers' fascia in three dimensions. It plays the role of a protective sheet for the neurovascular bundle. The optimal plane for nerve preservation is situated behind Denonvilliers' fascia. CONCLUSION: This study has enabled a clear visualization of the optimal planes to perform total mesorectal excision while ensuring nerve preservation. Three-dimensional visualization clearly helps to bridge the gap between histological examination and the findings of surgery.

3-Dimensional demonstration of fetal anal canal and sphincter.

PURPOSE: To identify the fetal anal canal and sphincter using 3-dimensional (3 D) ultrasound. MATERIALS AND METHODS: 3 D volumes of the fetal pelvis were acquired prospectively in 52 fetuses between 10 and 39 gestational weeks. A standard method for evaluating the fetal anal canal and sphincter was developed. Measurements of mucosal and muscular circumferences and the length of the anal canal were taken. RESULTS: The anal canal was demonstrated in 46 out of 50 patients (92 %). The sonographic characteristics of the anal canal in the axial plane appear like a "target sign" with an echogenic mucosa in the center, the hypoechoic internal sphincter muscle surrounding it and an outer echogenic circle reflecting the external sphincter. Measurements of mucosal and internal sphincter circumferences and the length of the anal canal demonstrated linear growth during pregnancy (p < 0.01). One case of anal atresia was demonstrated. CONCLUSION: The fetal anal canal can be visualized when a systematic analysis is performed using a 3 D volume dataset.

(Laterally) extended endopelvic resection: surgical treatment of locally advanced and recurrent cancer of the uterine cervix and vagina based on ontogenetic anatomy.

OBJECTIVE: Pelvic exenteration is mainly applied as a salvage operation for a subset of patients with persistent and recurrent cervicovaginal cancer. The procedure can also cure locally advanced primary disease not suitable for radiotherapy. However, high operative abortion and intralesional tumor resection rates significantly limit its clinical benefit. To improve locoregional tumor control we have proposed to establish cancer surgery on ontogenetic anatomy and, consequently, we have developed the (Laterally) Extended Endopelvic Resection ((L)EER). METHODS: (L)EER is clinically and histopathologically evaluated with a monocentric prospective observational study. Patients with advanced and recurrent cervicovaginal cancer are treatment candidates if distant metastases and tumor fixation at the region of the sciatic foramen can be excluded. RESULTS: 91 patients with locally advanced primary (n=30) and recurrent or persistent (n=61) carcinoma of the cervix and vagina were treated with (L)EER. 74% of the tumors were fixed to the pelvic wall. No (L)EER treatment was aborted, R0 resection was histopathologically confirmed in all cases. (L)EER definitively controlled the locoregional cancer in 92% (95% CI: 85-99) of the patients. Five year overall survival probability was 61% (95% CI: 49-72). CONCLUSIONS: The results of (L)EER treatment confirm the concept of cancer surgery based on ontogenetic anatomy. In patients with locally advanced and recurrent cervicovaginal cancer (L)EER achieves locoregional tumor control both with central disease and with tumors fixed to the pelvic side wall except at the region of the sciatic foramen.

The evolution, development and skeletal identity of the crocodylian pelvis: revisiting a forgotten scientific debate.

Unlike most tetrapods, in extant crocodylians the acetabulum is formed by only two of the three skeletal elements that constitute the pelvis, the ilium, and ischium. This peculiar arrangement is further confused by various observations that suggest the crocodylian pelvis initially develops from four skeletal elements: the ilium, ischium, pubis, and a novel element, the prepubis. According to one popular historical hypothesis, in crocodylians (and many extinct archosaurs), the pubis fuses with the ischium during skeletogenesis, leaving the prepubis as a distinct element, albeit one which is excluded from the acetabulum. Whereas the notion of a distinct prepubic element was once a topic of considerable interest, it has never been properly resolved. Here, we combine data gleaned from a developmental series of Alligator mississippiensis embryos, with a revised interpretation of fossil evidence from numerous outgroups to Crocodylia. We demonstrate that the modern crocodylian pelvis is composed of only three elements: the ilium, ischium, and pubis. The reported fourth pelvic element is an unossified portion of the ischium. Interpretations of pelvic skeletal homology have featured prominently in sauropsid systematics, and the unambiguous identification of the crocodylian pubis provides an important contribution to address larger scale evolutionary questions associated with locomotion and respiration.

Islet1 regulates establishment of the posterior hindlimb field upstream of the Hand2-Shh morphoregulatory gene network in mouse embryos.

How divergent genetic systems regulate a common pathway during the development of two serial structures, forelimbs and hindlimbs, is not well understood. Specifically, HAND2 has been shown to regulate Shh directly to initiate its expression in the posterior margin of the limb mesenchyme. Although the Hand2-Shh morphoregulatory system operates in both the forelimb and hindlimb bud, a recent analysis suggested that its upstream regulation is different in the forelimb and hindlimb bud. A combination of all four Hox9 genes is required for Hand2 expression in the forelimb-forming region; however, it remains elusive what genetic system regulates the Hand2-Shh pathway in the hindlimb-forming region. By conditional inactivation of Islet1 in the hindlimb-forming region using the Hoxb6Cre transgene, we show that Islet1 is required for establishing the posterior hindlimb field, but not the forelimb field, upstream of the Hand2-Shh pathway. Inactivation of Islet1 caused the loss of posterior structures in the distal and proximal regions, specifically in the hindlimb. We found that Hand2 expression was downregulated in the hindlimb field and that Shh expression was severely impaired in the hindlimb bud. In the Hoxb6Cre; Islet1 mutant pelvis, the proximal element that is formed in a Shh-independent manner, displayed complementary defects in comparison with Pitx1(-/-) hindlimbs. This suggests that Islet1 and Pitx1 function in parallel during girdle development in hindlimbs, which is in contrast with the known requirement for Tbx5 in girdle development in forelimbs. Our studies have identified a role for Islet1 in hindlimb-specific development and have revealed Islet1 functions in two distinct processes: regulation upstream of the Hand2-Shh pathway and contributions to girdle development.