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Vitreoretinal Surgery in Rare Conditions
Published in Pradeep Venkatesh, Handbook of Vitreoretinal Surgery, 2023
Retinal angiomas are rare tumours [hamartoma] that develop within the vascular bed of the retina. It may be sporadic or a part of the multisystem disorder, von Hippel Lindau [VHL] syndrome. VHL is inherited as an autosomal dominant disease with high penetrance and variable expressivity; the genetic defect being in the VHL gene located on the short arm of chromosome 3. These tumours express brachyury, FlK-1, and Scl, and so are thought to develop from embryologically arrested mesodermal cells programmed to develop into hemangioblasts. Tie-2 and CD31 endothelial markers have also been detected in these tumours. Other than retinal angiomas, VHL is associated with hemangioblastomas of the central nervous system (mainly infratentorial); renal cell carcinoma; pancreatic carcinoma; pheochromocytoma; and adrenal, pancreatic, and epidydimal cysts. Extraocular lesions could develop over a variable time frame, as late as the fifth decade of life, so periodic screening is recommended in all patients diagnosed with retinal angiomas.
Confusion with arteriovenous fistula versus arteriovenous malformation of ISSVA classification
Published in Byung-Boong Lee, Peter Gloviczki, Francine Blei, Jovan N. Markovic, Vascular Malformations, 2019
Developmental disorders develop in different stages during embryonic development. If a disorder occurs in the development from hemangioblast to angioblast, a vasculogenous defect develops and thus an extra-truncular vascular malformation. There are inter alia, diffuse short-circuit connections of arteries and veins: extra-truncular arteriovenous (AV) malformations.
Embryonic and Fetal Erythropoiesis
Published in Stephen A. Feig, Melvin H. Freedman, Clinical Disorders and Experimental Models of Erythropoietic Failure, 2019
D. Wade Clapp, Kevin M. Shannon
The mouse is the mammal in which the most comprehensive analyses of hematopoietic development have been performed. The first observed blood precursor cells, the hemangioblasts, are noted in the extraembryonic visceral mesoderm of the 7.5 to 8.5-day gestation embryo immediately adjacent to the endodermal cell layer.20–22 The hemangioblasts proliferate and segregate such that the peripheral cells become endothelial cells and the central cells become hematopoietic. The central cells contain the yolk sac pluripotent hematopoietic stem cells, and sites of cellular proliferation become blood islands. These islands eventually develop vascular communications — the genesis of the circulatory system.
Exploitation of receptor tyrosine kinases by viral-encoded growth factors
Published in Growth Factors, 2018
VEGFRs play critical roles in the formation, function and maintenance of the vasculature (Ferrara, 2004; Olsson et al., 2006). In the embryo, VEGFRs initiate vasculogenesis through in situ differentiation and growth of blood vessels from mesodermal-derived hemangioblasts. This gives rise to the heart and the first primitive vascular plexus. VEGFRs also regulate angiogenesis, in which existing lumen divide and endothelial cells sprout, migrate and proliferate to remodel and expand blood vessel networks. In mammals, these processes are regulated by three structurally-related VEGFRs, VEGFR1-3, which share a common extracellular domain composed of seven immunoglobulins (Ig)-like loops (Stuttfeld et al., 2009). These VEGFRs, however, display differences in ligand specificity, cellular signalling and biological effects.
Predictive modeling for cancer drug discovery using canine models
Published in Expert Opinion on Drug Discovery, 2020
Michael D. Lucroy, Mark A. Suckow
Canine hemangiosarcoma (HSA) is an aggressive, ultimately fatal, cancer arising from multipotential bone marrow-derived stem cells that arrest their differentiation at the hemangioblast or angioblast stage [60]. The spleen is the most common site of HSA in the dog, although liver, heart, skeletal muscle may also be sites of origin [61,62]. After splenectomy, or wide surgical excision at other sites, survival is short with death typically due to widespread metastasis often resulting in significant hemorrhage [61,63–67]. Angiosarcoma is a rare, aggressive cancer of people with similarly poor outcomes and few effective treatment options [68].
Hyalocyte origin, structure, and imaging
Published in Expert Review of Ophthalmology, 2022
Peter Wieghofer, Michael Engelbert, Toco YP Chui, Richard B Rosen, Taiji Sakamoto, J Sebag
Hematopoiesis can be subdivided into primitive hematopoiesis that is restricted to early embryonic development, and definitive hematopoiesis that takes place at later stages of development in the aorto-gonad-mesonephros (AGM) and the fetal liver (FL) as well as in the bone marrow established at the perinatal stages that remains active throughout life [52,53]. Primitive hematopoiesis is established in the hemogenic endothelium/hemangioblast of the extra-embryonic yolk sac that provides the blood island where precursors of both nucleated embryonic erythrocytes and primitive macrophages are created via the erythro-myeloid precursors (EMP) [54]. During development, EMPs further differentiate and their descendants colonize organs such as the brain or eye, before the intrinsic blood-brain or blood-retina barriers are formed, to become local tissue-resident macrophages including microglia [7,8,10,11,53,54]. Besides the developing organs that are reached via the embryonic circulation [3], they transiently colonize the fetal liver where progenitors of definitive hematopoiesis, derived from the AGM, can be found and establish the bone marrow later, prior to birth [53,55,56]. With regard to ciliary body macrophages, primitive hematopoiesis has been identified as the main source with only limited contribution from other hematopoietic organs including the fetal liver and the bone marrow [10]. With respect to hyalocytes, no embryonic fate mapping has been performed to date. However, human embryonic developmental stages have been investigated with respect to the local leukocyte populations by immunophenotyping [57]. The results suggest the presence of several markers that were attributed to hemangioblasts and suggested the existence of local blood islands remote from their well described localization in the yolk sac. Future experiments involving more contemporary methods including transcriptional profiling would help to decipher the former microscopic observations.