Hemangioma with dabskoid features: a rare histopathologic variant of acquired hemangioma

Benign and low-grade superficial endothelial cell neoplasms in the molecular era

Vascular tumors are the most common mesenchymal neoplasms of the skin and subcutis, and they encompass a heterogeneous group with diverse clinical, histological, and molecular features, as well as biological behavior. Over the past two decades, molecular studies have enabled the identification of pathogenic recurrent genetic alterations that can be used as additional data points to support the correct classification of these lesions. The purpose of this review is to summarize the available data related to superficially located benign and low-grade vascular neoplasms and to highlight recent molecular advances with the role of surrogate immunohistochemistry to target pathogenic proteins as diagnostic biomarkers.

Delimiting CD34+ Stromal Cells/Telocytes Are Resident Mesenchymal Cells That Participate in Neovessel Formation in Skin Kaposi Sarcoma

Kaposi sarcoma (KS) is an angioproliferative lesion in which two main KS cell sources are currently sustained: endothelial cells (ECs) and mesenchymal/stromal cells. Our objective is to establish the tissue location, characteristics and transdifferentiation steps to the KS cells of the latter. For this purpose, we studied specimens of 49 cases of cutaneous KS using immunochemistry and confocal and electron microscopy. The results showed that delimiting CD34+ stromal cells/Telocytes (CD34+SCs/TCs) in the external layer of the pre-existing blood vessels and around skin appendages form small convergent lumens, express markers for ECs of blood and lymphatic vessels, share ultrastructural characteristics with ECs and participate in the origin of two main types of neovessels, the evolution of which gives rise to lymphangiomatous or spindle-cell patterns-the substrate of the main KS histopathological variants. Intraluminal folds and pillars (papillae) are formed in the neovessels, which suggests they increase by vessel splitting (intussusceptive angiogenesis and intussusceptive lymphangiogenesis). In conclusion, delimiting CD34+SCs/TCs are mesenchymal/stromal cells that can transdifferentiate into KS ECs, participating in the formation of two types of neovessels. The subsequent growth of the latter involves intussusceptive mechanisms, originating several KS variants. These findings are of histogenic, clinical and therapeutic interest.

Cutaneous Vascular Neoplasms of Uncertain Biological Behavior

Neoplasms of uncertain biological behavior present physicians with a genuine conundrum in practice. Cutaneous vascular neoplasms within this category are exceedingly rare, possessing significant gaps and uncertainty in many facets of clinical practice. Firstly, lesions were selected for review based on their categorization as indeterminate behavior, indicating the potential for local recurrence and rarely metastasize. After identification of the target lesions, a comprehensive review of the literature using national databases produced several landmark studies and case series regarding these neoplasms. Limiting the review to only cutaneous limited tumors narrowed the pool of studies; however, quite a large sum of papers remained. Examination of each paper yielded beneficial results on diagnosing, effective treatments, follow-up findings, and prognosis for each indeterminate lesion discussed. Overall, the literature search combined the molecular, histologic, immunohistochemical, surgical strategies to develop an up-to-date and comprehensive framework to guide physicians when encountering such lesions. The tumors reviewed include: kaposiform hemangioendothelioma, endovascular papillary angioendothelioma, pseudomyogenic hemangioendothelioma, retiform hemangioendothelioma, epithelioid hemangioendothelioma, and composite hemangioendothelioma.

Piecemeal Mechanism Combining Sprouting and Intussusceptive Angiogenesis in Intravenous Papillary Formation Induced by PGE2 and Glycerol

Recently, we demonstrated that in human intravascular papillary endothelial hyperplasia (IPEH), vein wall vascularization occurs in association with myriad papillae, a large part of which formed in the vascularized vein wall. Previously, using an animal model, we observed that PGE2 and glycerol administration around the femoral vein originates intense vascularization of the vein wall from its intimal endothelial cells (ECs). This vascularization is similar to that in IPEH. The aim of this study is to assess the mechanism of papillary formation, using this model after demonstrating papillary development in neo-vascularized femoral vein walls. In semithin and ultrathin sections, the sequential vascular and papillary development was as follows: (a) activation of vein intimal ECs, (b) sprouting of intimal ECs towards the vein media layer and microvessel development, (c) interconnection between neighboring microvessels originated elementary loops, which encircled vein wall components and formed papillae. The encircling ECs formed the papillary cover, and the encircled component formed the core. The papillae showed a similar structure to that of folds and pillars in intussusceptive angiogenesis, and (d) origin of secondary and complex loop systems by interconnection of neighboring elementary loops and by splitting of papillae by new loops, with abundant papillary development. In conclusion, the results support a piecemeal angiogenic mechanism in papillary formation, with association of sprouting and intussusceptive types of angiogenesis. Further studies are needed to assess whether the intravascular papillae described in several pathologic processes, including vessel tumors, such as Dabska's tumor, retiform hemangioendothelioma, and angiosarcoma, follow a similar mechanism. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1781-1792, 2017. © 2017 Wiley Periodicals, Inc.