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.

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.

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.

Chronic ileal obstruction in adults due to peri-ileal vitelline vascular remnants.

Two young adults had distal ileal obstruction at sites where a fold of mesentery extended from its posterior leaf to the antimesenteric border of the bowel. No Meckel's diverticulum or mesoumbilical band was present in either case. Clinical, gross and microscopic findings suggested that the mesenteric fold represented a remnant of vitelline vessel that persisted in the peri-ileal portion of its course. Chronic ileal obstruction was apparently due to disordered peristalsis caused by the fold tethering the adjoining posterior bowel wall. In one patient, a chronic ulcer at the site of obstruction was interpreted as being an additional complication of the congenital lesion.