الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Vascular anomalies(VAs) represent a spectrum of disorders from a simple “birthmark” to life- threatening entities. Incorrect nomenclature and misdiagnoses are commonly experienced by patients with these anomalies. Accurate diagnosis is crucial for appropriate evaluation and management, often requiring multidisciplinary specialists. Classification schemes provide a consistent terminology and serve as a guide for pathologists, radiologists, clinicians, and researchers.
Over the past 2 decades, various subspecialists have adopted a new classification system proposed by the International Society for the Study of Vascular Anomalies (ISSVA), which divides vascular anomalies into 2 main categories: tumors and malformations. This system provides a systematic approach to VAs that correlates histopathology with clinical course and therapy.
Vascular tumors are endothelial neoplasms; they include the benign IHs and CHs as well as the borderline malignant rare KHEs, among others. IHs are by far the most common lesions; clinically they feature an early phase of rapid proliferation followed by a later stage of involution. Vascular malformations are developmental anomalies that are already present at birth but may go initially unnoticed. Unlike hemangiomas, they grow proportionately with the child and do not regress. They are subdivided into low- versus high flow malformations. Low flow malformations include various combinations of venous, capillary, and lymphatic elements, whereas high malformations have arterial component and include AVMs and AVFs.
The diagnosis of a soft-tissue VA is primarily based on the clinical examination. Imaging is usually reserved for therapeutic planning, and lesions with unclear diagnosis or deep-tissue involvement. Currently, US and MRI are the two noninvasive imaging techniques of choice. Gray-scale US with color Doppler assessment is a good imaging modality for the initial assessment and characterization of such lesions because it enables differentiation of high- from low-flow lesions. Its main limitations are insufficient FOV and tissue penetration as well as operator dependency. Many VAs grow in an infiltrative fashion and can involve multiple tissue planes. MRI helps overcome all these limitations and provides superior tissue characterization. It is unsurpassed in showing lesion extent and involvement of different tissue planes and joints. The anatomic extent of the lesion is best seen on fluid-sensitive sequences, such as fat-suppressed fast spin-echo (FSE) T2-weighted or STIR imaging.
Differentiation between high flow and low flow lesions is crucial. In conventional MR images, the presence of vascular signal voids and phleboliths can help in differentiation between them. In high flow lesions, high-flow vessels appear as signal voids on spin-echo (SE) sequences and hyperintense foci on gradient-recalled echo (GRE) sequences. Phleboliths are characteristic for low flow lesions and appear signal void foci in all sequences and can be easily differentiated from vascular signal void on contrast enhanced and GRE sequences.
Furthermore, dynamic TR MRA permits determination of the flow hemodynamics within the lesion. High-flow lesions on DCE-MRI demonstrate contrast enhancement at or preceding arterial enhancement of the main artery in the region of interest while low-flow lesions do not appear on DCE-MRI images until the venous phases.
Semi-quantitative perfusion images in our study showed preliminary good results as an objective method in characterization of the hemodynamics of the VAs. High flow lesions have significantly shorter artery-lesion enhancement time and maximal lesional enhancement time.