Aneurysmal dilatation of persistent vitelline vein with thrombus in a neonate.

The paired vitelline veins selectively involute and form a part of the portal vein during embryonic development. The presence of a persistent vitelline vein segment after birth is very rare and can be confused with anomalies of the portal and umbilical veins. We present sonographic, CT and MRI findings of aneurysmal dilatation of a persistent vitelline vein with thrombus in a neonate; this case was first misdiagnosed as an umbilical vein varix by prenatal US. MRI was used to identify the persistent vitelline vein segment and the remnant umbilical vein segment.

Fetal MRI as a complementary technique after prenatal diagnosis of persistent vitelline artery in an otherwise normal fetus.

Prenatal ultrasound is the standard for the diagnosis of fetal anomalies. However, fetal MRI has emerged as a valuable diagnosis tool to complete the study of fetal malformations. Type II single umbilical artery results from the absence of both umbilical arteries and persistence of the vitelline artery. It has been described only in fetuses with sirenomelia or caudal regression syndrome. We report a favorable outcome in a normal fetus in which prenatal ultrasound and MRI showed a single umbilical artery arising from the aorta. The etiology of such a finding and its possible consequences are discussed.

Mouse extraembryonic arterial vessels harbor precursors capable of maturing into definitive HSCs.

During mouse development, definitive hematopoietic stem cells (dHSCs) emerge by late E10.5 to E11 in several hematopoietic sites. Of them, the aorta-gonad-mesonephros (AGM) region drew particular attention owing to its capacity to autonomously initiate and expand dHSCs in culture, indicating its key role in HSC development. The dorsal aorta contains characteristic hematopoietic clusters and is the initial site of dHSC emergence, where they mature through vascular endothelial (VE)-cadherin(+)CD45(-)CD41(low) (type 1 pre-HSCs) and VE-cadherin(+)CD45(+) (type 2 pre-HSCs) intermediates. Although dHSCs were also found in other embryonic niches (placenta, yolk sac, and extraembryonic vessels), attempts to detect their HSC initiating potential have been unsuccessful to date. Extraembryonic arterial vessels contain hematopoietic clusters, suggesting that they develop HSCs, but functional evidence for this has been lacking. Here we show that umbilical cord and vitelline arteries (VAs), but not veins, contain pre-HSCs capable of maturing into dHSCs in the presence of exogenous interleukin 3, although in fewer numbers than the AGM region, and that pre-HSC activity in VAs increases with proximity to the embryo proper. Our functional data strongly suggest that extraembryonic arteries can actively contribute to adult hematopoiesis.

Vascular remodeling of the vitelline artery initiates extravascular emergence of hematopoietic clusters.

The vitelline artery is a temporary structure that undergoes extensive remodeling during midgestation to eventually become the superior mesenteric artery (also called the cranial mesenteric artery, in the mouse). Here we show that, during this remodeling process, large clusters of hematopoietic progenitors emerge via extravascular budding and form structures that resemble previously described mesenteric blood islands. We demonstrate through fate mapping of vascular endothelium that these mesenteric blood islands are derived from the endothelium of the vitelline artery. We further show that the vitelline arterial endothelium and subsequent blood island structures originate from a lateral plate mesodermal population. Lineage tracing of the lateral plate mesoderm demonstrates contribution to all hemogenic vascular beds in the embryo, and eventually, all hematopoietic cells in the adult. The intraembryonic hematopoietic cell clusters contain viable, proliferative cells that exhibit hematopoietic stem cell markers and are able to further differentiate into myeloid and erythroid lineages. Vitelline artery-derived hematopoietic progenitor clusters appear between embryonic day 10 and embryonic day 10.75 in the caudal half of the midgut mesentery, but by embryonic day 11.0 are sporadically found on the cranial side of the midgut, thus suggesting possible extravascular migration aided by midgut rotation.

Hemodynamics of the omphalo-mesenteric arteries in stage 18 chicken embryos and "flow-structure" relations for the microcirculation.

OBJECTIVE: The primary objective of this study is to evaluate the hemodynamic and structural characteristics of the omphalo-mesenteric (vitelline) arteries in stage 18 chicken embryos. The measured results were compared with Murray's law to validate the theoretical prediction on the vascular structure. METHODS: Variation of hemodynamic parameters such as mean velocity (U(mean)), peak velocity (U(peak)) at the systolic phase, velocity fluctuations (U(fluc)) at the pulsatile frequency, and the Womersley number (Ω) were measured with respect to the geometric parameters including the bifurcation cascade level (BCL), vessel diameter (D), and distance (L) from the first bifurcation. They were assessed by using the time-resolved in vivo micro-PIV (particle image velocimetry) technique and the geometric information was obtained from the microscopic vessel images. RESULTS: The effect of "branching of the vessel" on the variation of hemodynamic characteristics is similar to those of the "increase in distance" from the first bifurcation and the "decrease in vessel diameter". The flow quantities (U(mean), U(peak) and U(fluc)) decrease due to the increase in cross-sectional area ratio (γ=1.209=(∑D(daughter)(2))/D(mother)(2)), and the Womersley number also decreases as the bifurcation cascades (Ω«1). CONCLUSION: The geometric parameters are closely related to the variation of hemodynamic characteristics. Murray's law with non-constant viscosity hypothesis would provide an insight on the two-phase nature of microvascular blood flows.

Two different pathways for the transport of primitive and definitive blood cells from the yolk sac to the embryo in humans.

During the early human embryonic period nutrients and blood cells are temporarily provided by the extraembryonic yolk sac (YS). The YS before week six is involved not only in primitive but also in definitive erythropoiesis. While the destiny of primitive erythroid cells that fill the blood vessels of the YS is well known, the final destination of erythrocytes present in the endodermal vesicular system is unknown. In the present study we have investigated, step by step, the destiny of the erythrocytes present in the endodermal vesicles during the embryonic period. Twelve human YSs and their corresponding yolk stalks were analyzed between weeks 4 and 7 of embryonic age by light and scanning electron microscopy. It is shown that erythrocytes (according to their size and morphological features) located within the endodermal vesicles of the YS wall are pulled out through endodermal pits into the YS cavity, from where they reach the lumen of the primitive gut of the embryo through the vitelline duct, a temporary pathway communicating both compartments. During the study period no erythrocytes were seen within the embryo's vascular network where only primitive erythroblasts were identified. Our results indicate that the vitelline duct plays an important transient role as a pathway for the transport of nutrients and blood cells between the YS and the embryo before week five of embryonic development that ends just at the time when YS-embryo circulation becomes established.

Antenatal sonographic features of aneurysmal dilatation of a vitelline vein.

We report a case of aneurysmal dilatation of a vitelline vein observed antenatally. Intra-abdominal vascular dilatation was diagnosed on ultrasound examination at 24 weeks' gestation. The relationship with the umbilicus and portal vein suggested the diagnosis of umbilical vein varix. Fetal tolerance remained excellent in spite of a gradual increase in the size of the dilated vein. Postnatal ultrasound examination revealed thrombosis of the aneurysm with gradual extension to the portal vein and the onset of serious coagulation problems. Operative findings on postnatal day 9 included the absence of intra-abdominal umbilical vein, and the presence of an abnormal, dilated and thrombosed vein connecting the umbilicus to the portal vein and following the trajectory of the right vitelline vein. Corrective surgery was attempted by resection of the aneurysm and portal thrombectomy, but this did not prevent the development of portal obstruction syndrome with cavernous hemangioma. This anomaly, in which the fetal venous return uses the vitelline vein in the absence of the umbilical vein, does not appear to have been described before. The mechanism in question could be anastomosis between the right vitelline vein and umbilical vein. Antenatal diagnosis should enable early surgical management before the formation of a portal thrombosis.

Neonatal intestinal volvulus due to a persistent right vitelline artery.

We report a case of neonatal intestinal volvulus around a persistent right vitelline artery, presenting as an aberrant parieto-mesenteric band on exploratory laparotomy. To our knowledge, this is the first case report in the English literature of a persistent right vitelline artery causing axial intestinal volvulus in a neonate. A review of the literature and the embryopathogenesis is discussed, as well as the importance of emergent diagnoses of such lesions.

Emergence of a glomus-like body in the human yolk sac: a microanatomical analysis of its structure.

Since the last decade the Yolk sac (YS) has been a topic of increasing interest due to the growing use of high-resolution sonography in early determination of pregnancy. Human YS shape and diameter are indicators of viability of pregnancy during the early embryonic period. Nevertheless, the major interest concerns the vital function it plays in early embryo growth and development. Two compartments are recognized in this organ: the yolk sac proper and the vitelline stalk. In this study we report the identification and partial characterization of a glomus-like body in the wall of the secondary YS in humans. A detailed structural description is also presented on the time course of formation of this new structure, at precisely sequential stages between 4-8 wk post-conception. The significance of this new compartment on the YS function is analyzed. Light and scanning electron microscopy were used to investigate the microstructure of the YS and the vitelline stalk during the first 8 wk of development. Ten YSs were collected from embryos (aged between 24-50 days) obtained from emergency salpingectomies due to tubal ectopic pregnancy. From 5 wk onward a new structure was observed in the YS located near the apex of the pear-shaped yolk vesicle and closed to the connecting stalk. We designate this differentiation as glomus-like body. This structure is 1-1.5 mm long and merged from a pocket-like structure of the extraembryonic splanchnic mesoderm of the YS wall. It likely represents an area of convergence of the vascular network of the YS wall. Our findings underline the remarkable complexity of the human secondary yolk sac during early development. The detailed description of the microanatomy of this vital organ is of theoretical and practical interest in order to unravel the mechanisms used by the yolk sac to transport nutrients to the embryo.

Type II single umbilical artery (persistent vitelline artery) in an otherwise normal fetus.

A single umbilical artery resulting from absence of the umbilical arteries and persistence of the vitelline artery that arises directly from the abdominal aorta has been described only in malformed fetuses with sirenomelia or caudal regression. Such an aberrant artery was suggested to be the etiology of sirenomelia caused by a 'steal' mechanism of blood flow from the caudal end of the embryo. We present a case in which prenatal ultrasound showed a similar aberrant single artery arising from the abdominal aorta in an otherwise normal fetus with a normal course of pregnancy. This vessel, a continuation of the superior mesenteric artery (SMA), corresponds to a persistent vitelline artery assuming the function of the umbilical arteries. The etiology of such a finding and its possible consequences are discussed.

Volume and vascularity of the yolk sac assessed by three-dimensional and power doppler ultrasound.

The yolk sac is an organ of increasingly recognized importance in the initial mechanisms of pregnancy maintenance and the early growth and welfare of the embryo. The aim of our study was to assess the vascularity of the yolk sac and vitelline duct in 150 patients between the 6th and 10th weeks of normal, and uncomplicated pregnancies who were scheduled for termination of pregnancy for psychosocial reasons and 130 complicated pregnancies. In same patients volume of the yolk sac was assessed using Combison 530 3D Voluson, Medison-Kretz Company. Overall visualization rate for yolk sac vessels was 80,38%. The highest visualization rates were obtained in the 7th and 8th weeks of gestation reaching values of 90,71 %. In the same period the visualization rates of the vitelline duct arteries were 87,71% and 91,28% respectively. A characteristic waveform profile included low velocity (5,8+/-1,7 cm/s) and absence of diastolic flow which was obtained from all examined yolk sacs. The PI showed the mean value of 3,24+/-0,94 without significant changes between subgroups (p>0,05). Vitelline vessels showed similar PSV (5,4+/-1,8 cm/s) and PI values (3,14+/0,91) (p>0,05) to that obtained from the yolk sac. Three types of abnormal vascular signals were derived from the yolk sac in patients with missed abortion (n=32): irregular blood flow (n=6), permanent diastolic flow (n=2) and venous blood flow signals (n=5). However, in the most of the patients (n=19) blood flow signals could not have been extracted from these early embryonic structures. Using three-dimensional ultrasound we found a positive correlation between gestational age and volumes of the gestational and yolk sac until 10 weeks gestation. At the end of the first trimester yolk sac volume remained constant, while gestational sac volume continued to grow. It seems that changes in both yolk sac appearance (size, shape, volume and echogenicity) and vascularization are probably a consequence of poor embryonic development or even embryonic death, rather than being a primary cause of an early pregnancy failure.

Persistent vitelline vein in a foal.

A three-day-old foal died from intestinal strangulation due to a remnant of vitelline vein which extended between the umbilicus and the portal vein. The strangulating vein was identified on the basis of its morphological and histological structure. This finding, which is the first reported case of a persistent vitelline vein in a horse, is discussed in relation to the normal development and involution of the vitelline circulation.

Meckel's diverticulum: angiographic findings in 16 patients.

OBJECTIVE: The purpose of this study was to assess the sensitivity of angiography in revealing the vitellointestinal artery or other arteriographic abnormalities in patients in whom surgery subsequently proved Meckel's diverticulum. MATERIALS AND METHODS: From the 36 patients who had undergone a Meckel's diverticulectomy between 1980 and 1997 at Hammersmith Hospital or a referring hospital, we selected 18 who had undergone preoperative angiography at our institution. Case notes and angiograms of these 18 patients were reviewed for the presence of a persistent vitellointestinal artery or other angiographic evidence of a Meckel's diverticulum. RESULTS: Angiograms of 16 of 18 patients were available for review. A striking male preponderance existed (male:female = 13:3). Mean age was 28 years (range, 12-65 years). In 11 (69%) of the 16 patients, a persistent vitellointestinal artery was seen that had been noted at the time of the study and reported before surgery for nine patients. Other angiographic abnormalities at the site of the Meckel's diverticulum were present in four patients and included a vascular blush, early venous return, and arterial irregularity. CONCLUSION: Angiography will show a persistent vitellointestinal artery in most individuals with a Meckel's diverticulum who present with chronic gastrointestinal bleeding. However, the recognition of a persistent vitellointestinal artery may be difficult because of overlying vessels, and superselective catheterization of distal ileal arteries may be necessary.

Vascular effects of endothelin-1 in stage 21 chick embryos.

Endothelin-1 is a very potent vasoconstrictor, but its function has not yet been investigated in the early stage of cardiovascular development. The purpose of the present study was to clarify whether endothelin-1 exerts a hemodynamic effect in stage 21 chick embryos. We measured vitelline artery blood pressure with a servo-null micropressure system and blood flow velocity at the dorsal aorta with a 20 MHz pulsed Doppler velocity meter. The vitelline vessels were directly measured with a microscope video system. While monitoring these parameters, endothelin-1 was infused into a vein by a microinjector and data were collected. Endothelin-1 increased the blood pressure and heart rate, but decreased the dorsal aortic blood flow. Only the vitelline veins with a diameter of between 100 and 200 microm constricted after endothelin infusion, but smaller or larger veins and the arteries did not show any significant change in size, although the resistant arteries could not be measured by this method. In conclusion, endothelin-1 has apparent constrictive effects in the selected vessel in the early stages of cardiovascular development when the endocrine and autonomic nervous systems have not yet developed.

Vascularization of yolk sac and vitelline duct in normal pregnancies studied by transvaginal color and pulsed Doppler.

The yolk sac is an organ of increasingly recognized importance in the initial mechanisms of pregnancy maintenance and the early growth and welfare of the embryo. Having a complex protein secretion and an equally intricate ultrastructure, it is the primary source of blood and germ cells. This small and to date largely ignored structure may have a vital and interesting part to play in human embryonic development, which may be comparable to its proven evolutionary importance in other animals. The aim of our study was to assess the vascularity of the yolk sac and vitelline duct in 105 patients between the 6th and 10th weeks of gestation who were scheduled for termination of pregnancy for psychosocial reasons. The patients were divided in five subgroups depending on the duration of gestation. All of them had a normal developing pregnancy with no clinical symptoms of pathology (e.g. bleeding in early pregnancy). Gestational age was calculated from the first day of the last menstrual period and substantiated by crown-rump (CRL) measurements. After exploration of the gestational sac and embryo by transvaginal sonography, color Doppler was used to image the yolk sac and vitelline duct vascularity. The visualized vessels were analyzed with pulsed Doppler using the sample volume unit set of 1 mm. The assessment of obtained waveform signals was made by means of peak systolic Doppler shift (PSV) and pulsatility index (PI). The pulsatility index was calculated as a difference between peak systolic and end diastolic Doppler shift divided by the mean maximum velocity. At least 5 separate cardiac cycles were measured, and the mean value was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)