ISSVA Classification of Vascular Anomalies and Molecular Biology.

Vascular anomalies include various diseases, which are classified into two types according to the International Society for the Study of Vascular Anomalies (ISSVA) classification: vascular tumors with proliferative changes of endothelial cells, and vascular malformations primarily consisting of structural vascular abnormalities. The most recent ISSVA classifications, published in 2018, detail the causative genes involved in many lesions. Here, we summarize the latest findings on genetic abnormalities, with the presentation of the molecular pathology of vascular anomalies.

Update and audit of the St George's classification algorithm of primary lymphatic anomalies: a clinical and molecular approach to diagnosis.

Primary lymphatic anomalies may present in a myriad of ways and are highly heterogenous. Careful consideration of the presentation can lead to an accurate clinical and/or molecular diagnosis which will assist with management. The most common presentation is lymphoedema, swelling resulting from failure of the peripheral lymphatic system. However, there may be internal lymphatic dysfunction, for example, chylous reflux, or lymphatic malformations, including the thorax or abdomen. A number of causal germline or postzygotic gene mutations have been discovered. Some through careful phenotyping and categorisation of the patients based on the St George's classification pathway/algorithm. The St George's classification algorithm is aimed at providing an accurate diagnosis for patients with lymphoedema based on age of onset, areas affected by swelling and associated clinical features. This has enabled the identification of new causative genes. This update brings the classification of primary lymphatic disorders in line with the International Society for the Study of Vascular Anomalies 2018 classification for vascular anomalies. The St George's algorithm considers combined vascular malformations and primary lymphatic anomalies. It divides the types of primary lymphatic anomalies into lymphatic malformations and primary lymphoedema. It further divides the primary lymphoedema into syndromic, generalised lymphatic dysplasia with internal/systemic involvement, congenital-onset lymphoedema and late-onset lymphoedema. An audit and update of the algorithm has revealed where new genes have been discovered and that a molecular diagnosis was possible in 26% of all patients overall and 41% of those tested.

Quadrifurcation Variants of the Celiac Trunk.

BACKGROUND: The celiac trunk (CT) commonly trifurcates into the left gastric artery, common hepatic artery (CHA), and splenic artery (SA). The CHA then sends off the proper hepatic artery and gastroduodenal artery (GDA). The arcades of the head of the pancreas are celiacomesenteric anastomoses between branches of the GDA and the superior mesenteric artery. A quadrifurcation of the CT commonly occurs when a different branch is added to the 3 normal ones. An uncommon quadrifurcation of the CT occurs when only one or 2 of the normal branches of the CT participate. METHODS: The CT quadrifurcations were documented on 112 computed tomography angiograms. RESULTS: Five different types of CT quadrifurcation-3 uncommon (types 1-3) and 2 common (types 4-5)-were found in 15/112 cases (13.39%). A marginal significant association was found between the presence of quadrifurcations and male gender (P = 0.05; Fisher's exact test). Type 1 showed a hepatogastric trunk+SA + right hepatic artery+GDA pattern, type 2 had an HGT + right inferior phrenic artery + CHA + SA pattern, type 3 had a gastrophrenic trunk + left inferior phrenic artery+CHA + SA pattern, type 4 showed an left gastric artery + CHA + SA + left inferior phrenic artery combination, and type 5 had an additional common inferior phrenic trunk. One of the type 4 cases showed a buildup of a mesentericomesenteric anastomotic pancreatic arcade between the inferior pancreaticoduodenal arteries, rather than a celiacomesenteric one. CONCLUSIONS: Anatomic variation of the celiacomesenteric axis is important during hepatobiliary and duodenopancreatic approaches. Therefore, preoperative evaluation is essential because theoretical anatomic possibilities could be real arterial variants.

Genes and phenotypes in vascular malformations.

Vascular malformations (VMs) are caused by localized defects of vascular development. Most VMs are due to sporadic, postzygotic mutations, while some are the result of autosomal dominant germline mutations. Genotype-phenotype correlation is influenced by many factors. Individual genes can induce different phenotypes (pleiotropy), and similar phenotypes can be due to different genes/mutations (redundancy). The phenotypic spectrum of somatic mutations is wide, and depends on variant allele frequency, timing during embryogenesis, cell type(s) involved and type of mutation. The phenotype of germline mutations is determined by penetrance and expressivity, and is influenced by epigenetic factors (DNA methylation, histone modification) or 'second-hit' somatic mutations. Except for disorders with pathognomonic phenotypes such as Proteus syndrome or a characteristic constellation of symptoms such as CLOVES [congenital lipomatous (fatty) overgrowth, vascular malformations, epidermal naevi and scoliosis/skeletal/spinal anomalies] or PIK3CA-related overgrowth spectrum syndrome, differential diagnosis of VM is therefore difficult. It will be greatly facilitated with increasing analytic sensitivity of sequencing techniques such as next-generation sequencing. High-sensitivity molecular techniques are a prerequisite for targeted pharmacotherapy, i.e. selective therapeutic inhibition of activating mutations underlying VM, which has shown promising results in preliminary studies.

Thermography for the differential diagnosis of vascular malformations.

Vascular malformations classification may pose a diagnostic challenge for physicians. In the early stages, they are diagnosed clinically mainly by visual inspection. For a deeper analysis, Doppler ultrasonography is the preferred technique to determine the haemodynamic behaviour of the anomaly. However, this imaging method is not always available and it requires trained operators to acquire and interpret the images. There is a lack of portable and user-friendly systems that may help physicians in the assessment of vascular malformations. We propose a new diagnostic procedure, more affordable and easier to use, based on a portable thermal camera. This technique provides information about temperature, which has been found to be correlated with the flow rate of the lesion. In our study, > 60 vascular malformations of previously diagnosed patients were analysed with a thermal camera to classify them into low-flow and high-flow malformations. The value was 1 for both sensitivity and specificity of this technique.

Emerging importance of molecular pathogenesis of vascular malformations in clinical practice and classifications.

Vascular malformations occur during early vascular development resulting in abnormally formed vessels that can manifest as arterial, venous, capillary or lymphatic lesions, or in combination, and include local tissue overdevelopment. Vascular malformations are largely caused by sporadic somatic gene mutations. This article aims to review and discuss current molecular signaling pathways and therapeutic targets for vascular malformations and to classify vascular malformations according to the molecular pathways involved. A literature review was performed using Embase and Medline. Different MeSH terms were combined for the search strategy, with the aim of encompassing all studies describing the classification, pathogenesis, and treatment of vascular malformations. Major pathways involved in the pathogenesis of vascular malformations are vascular endothelial growth factor (VEGF), Ras/Raf/MEK/ERK, angiopoietin-TIE2, transforming growth factor beta (TGF-ß), and PI3K/AKT/mTOR. These pathways are involved in controlling cellular growth, apoptosis, differentiation, and proliferation, and play a central role in endothelial cell signaling and angiogenesis. Many vascular malformations share similar aberrant molecular signaling pathways with cancers and inflammatory disorders. Therefore, selective anticancer agents and immunosuppressants may be beneficial in treating vascular malformations of specific mutations. The current classification systems of vascular malformations, including the International Society of the Study of Vascular Anomalies (ISSVA) classification, are primarily observational and clinical, and are not based on the molecular pathways involved in the pathogenesis of the condition. Several molecular pathways with potential therapeutic targets have been demonstrated to contribute to the development of various vascular anomalies. Classifying vascular malformations based on their molecular pathogenesis may improve treatment by determining the underlying nature of the condition and their potential therapeutic target.

Benign vascular anomalies: A transition from morphological to etiological classification.

The International Society for the Study of Vascular Anomalies (ISSVA) devised a multidisciplinary etiopathogenesis based approach to classify benign vascular anomalies into tumors and malformations. This classification scheme has major therapeutic and prognostic implications as treatment modalities differ for both the categories. Inappropriate usage of the term "hemangioma" for etiopathogenetically distinct entities is commonly seen in clinical practice leading to delivery of incorrect treatment to the patients. We aimed to study the histomorphological and immunohistochemical features of benign vascular anomalies for their precise histopathological classification. A total of 48 cases diagnosed over a period of 3.5 years were reviewed and reclassified into vascular tumors and malformations based on ISSVA classification and prototypical histopathological features. Biopsies were reviewed based on 5 histopathological criteria viz. endothelial morphology, mitotic activity, intralesional nerve bundles, intralesional inflammation, and prominent vessel type. A panel of GLUT-1, WT-1, and Ki-67 was performed in each case. Seven cases of infantile hemangioma, 4 cases each of non-involuting congenital hemangioma and pyogenic granuloma, and 33 cases of vascular malformations were diagnosed. Endothelial cell morphology (p < 0.001), mitotic activity (p < 0.001), and intralesional nerve bundles (p < 0.001) were found to be statistically significant in differentiating hemangioma from malformations. GLUT-1 (p < 0.001) and Ki-67 labeling index (p < 0.001) were useful to distinguish infantile hemangioma from vascular malformations. To conclude, the ISSVA classification of benign vascular anomalies can be reliably done on histopathology. However, every case must be interpreted in the light of clinical and radiological features.

Radiological classification of azygos anterior cerebral artery and evaluation of the accompanying vascular anomalies.

PURPOSE: There is not a classification of azygos anterior cerebral artery (ACA) based on anatomical branching levels in the literature. In the present study, a classification of azygos ACA was made based on radiological imaging for a common terminology, and frequency, accompanying vascular anomalies and malformations were investigated. METHODS: A total of 4913 cases who had brain CTA, MRA, contrast-enhanced MRI and DSA in January 2010-January 2020 period were screened for the study. Based on anatomical branching level, azygos ACAs were classified into four groups. Aneurysms, anomalies and malformations accompanying azygos ACA were identified. The associations of azygos ACA types with the presence of aneurysm or ACA A1 segment anomalies were investigated. RESULTS: Azygos ACA was observed in 57 cases (29 male and 28 female) and frequency of azygos ACA was 1.16%. Average age of the cases with ACA was 56.19 ± 19.65 years. Forty-eight of the cases had type C azygos ACA, four cases type B, four cases type D and one case type A azygos ACA. A total of nine intracranial aneurysms were identified in seven of the cases (12.28%). Five of the aneurysms were located in MCA and four in distal ACA. Most common vascular anomalies accompanying azygos ACA were unilateral vertebral artery hypoplasia and ACA A1 segment hypoplasia. Azygos types did not have significant correlations with the presence of aneurysms or ACA A1 segmental anomalies (p = 0.683 and p = 0.949, respectively). CONCLUSION: Azygos ACA is a rare variation, but it could be accompanied by aneurysms or other vascular anomalies.

Hepatic arterial system anomalies encountered during pancreaticoduodenectomy - our experience.

We present our experience of incidence and management of aberrant hepatic arterial anatomy encountered during pancreaticoduodenectomy (PD). Patients undergoing PD between December 2014 and November 2016 at the Shaukat Khanum Memorial Cancer Hospital, Lahore were included in this short report. Preoperative imaging and operative findings of these patients were reviewed to evaluate the hepatic arterial anatomy and classified according to Hiatt classification. Sixty-four PD were performed with aberrant arterial anatomy identified in 24 (37.5%) of the cases. Most common anomaly was replaced right hepatic artery (rRHA) arising from the superior mesenteric artery seen in seven (11%) of the patients. Aberrant vessels were recognised and preserved in 23 cases. In one patient, the rRHA was coursing through the pancreatic parenchyma needing resection and reconstruction with uneventful postoperative recovery. Hepatic arterial anomalies are common and it is possible to preserve these vessels with careful surgical dissection using artery first technique.

Guidance Document for Hepatic Hemangioma (Infantile and Congenital) Evaluation and Monitoring.

OBJECTIVE: To define the types of hepatic hemangiomas using the updated International Society for the Study of Vascular Anomalies classification and to create a set of guidelines for their diagnostic evaluation and monitoring. STUDY DESIGN: We used a rigorous, transparent consensus protocol defined by an approved methodology, with input from multiple pediatric experts in vascular anomalies from hematology-oncology, surgery, pathology, radiology, and gastroenterology. RESULTS: In the first section, we define the subtypes of hepatic hemangiomas based on the clinical course, histology, and radiologic characteristics. We recommend against using the term "hemangioma" for any vascular malformations affecting the liver or any hypervascular tumors that are not characterized by the approved definitions. We recommend against using the term "hemangioendothelioma" for infantile or congenital hemangioma. The following 2 sections dedicated to infantile hepatic hemangioma and to congenital hepatic hemangioma individually describe these subtypes in further detail, including complications to be considered during monitoring and respectively recommended screening evaluations. CONCLUSIONS: Although institutional variations may exist for specific clinical details, a clear understanding of the diagnosis of hepatic hemangiomas affecting children and the possible complications that require screening during the monitoring period should be standard. As children with hepatic hemangiomas are managed by different medical and surgical specialties, we offer an expert opinion multidisciplinary consensus based on current literature and on data extracted from the liver hemangioma registry.

Duplicated Prostate Artery Central Gland Blood Supply: A Retrospective Analysis and Classification System.

Angiograms and cone-beam computed tomography scans of 36 consecutive prostate artery embolization patients (72 hemipelves) between October 2014 and February 2018 were reviewed. The hemipelves were classified according to the presence of dual central gland (CG) blood supply and the pattern of vascularization: Type 1 with a single CG blood supply (83.3%; n = 60); Type 2 with 2 independent CG arteries with overlapping territories (9.7%; n = 7); and Type 3 with 2 independent CG arteries with isolated territories (7%; n = 5). Up to 20% of pelvic sides may have more than 1 independent CG prostate artery that should be searched for during prostate artery embolization.

Inconsistency in classifying vascular anomalies: What's in a name?

BACKGROUND: Vascular anomalies are a heterogeneous group of disorders seen in children and adults. A standard nomenclature for classification has been offered by the International Society for the Study of Vascular Anomalies. Its application is important for communication among the multiple specialties involved in the care of patients and for planning treatment, as well as for research and billing. We hypothesized that terminology still is not uniformly applied, and that this could have an impact on treatment. METHODS: We retrospectively reviewed the medical records of patients with nonbrain lesions from our institutional vascular anomalies database seen during 2010-2016 for whom at least one clinic visit, radiologic imaging report, and pathology report were available to compare diagnoses among and within disciplines, and treatment recommendations. Diagnoses and referral patterns by community healthcare providers were also reviewed. RESULTS: Of 400 patients seen during the targeted time interval, 35 had clinical, imaging, and pathology reports. Agreement in terminology from initial clinic notes with imaging and pathology reports was noted in only three cases (9%). "Hemangioma" was often misused; "lymphangioma" and "cystic hygroma" persist as diagnostic labels. Community healthcare providers referred vascular malformations with a diagnosis of "mass" or "hemangioma" in 17 of 18 cases where that information was available. Incomplete or mislabeling of vascular anomalies sometimes delayed referrals to appropriate clinics, though it did not have a major impact on treatment. CONCLUSIONS: An understanding of vascular anomalies as tumors or malformations is not uniform. Ongoing education will be needed to promote consensus terminology and facilitate referrals.

Magnetic Resonance Imaging of the Soft Tissue Vascular Anomalies in Torso and Extremities in Children: An Update With 2014 International Society for the Study of Vascular Anomalies Classification.

Vascular anomalies can occur anywhere in the body, and the majority present in the pediatric population. Accurate classification is essential for proper clinical evaluation, particularly because multidisciplinary care is often required. The International Society for the Study of Vascular Anomalies classification offers a comprehensive classification for all subspecialties. In this review article, we present a magnetic resonance imaging protocol with exemplary cases of the most common types of vascular anomalies in the pediatric trunk and extremities using the current International Society for the Study of Vascular Anomalies classification.

Update on classification and diagnosis of vascular malformations.

PURPOSE OF REVIEW: This review provides an update of the classification in the classification of vascular anomalies since April 2014 at the International Society for the Study of Vascular Anomalies meeting in Melbourne, Australia. RECENT FINDINGS: The reader will become familiar with how to diagnose the major vascular malformations, including capillary, venous, arteriovenous, and lymphatic and combinations thereof. In addition, vascular malformation syndromes, including those with overgrowth, will be clarified. SUMMARY: Vascular malformations are common. Capillary malformations are now better understood through an updated classification. Verrucous hemangioma is truly a venulocapillary malformation that extends into the subcutis. PIK3Ca-Related Overgrowth Syndromes encompass Klippel-Trenaunay, Congenital Lipomatous Asymmetric Overgrowth of the Trunk with Lymphatic, Capillary, Venous, and Combined-Type Vascular Malformations, Epidermal Nevi, Scoliosis/Skeletal and Spinal Anomalies, Megalencephaly-Capillary Malformation-Polymicrogyria Syndrome (M-CAP), fibroadipose hyperplasia, and macrodactyly. Yet another syndrome should be highlighted: Capillary Malformation of the Lower Lip, Lymphatic Malformation of the Face and Neck, Asymmetry and Partial/Generalized Overgrowth. Knowledge of the genetic basis of vascular malformations will lead to future treatments.

Phosphoinositide 3-kinase: a new kid on the block in vascular anomalies.

Vascular anomalies are broadly divided into vascular tumours and malformations. These lesions are composed of abnormal vascular elements of various types, and mainly affect infants, children, and young adults. Vascular anomalies may be painful, may be complicated by bleeding, infection, or organ dysfunction, and can have secondary effects on other tissues. Current treatment strategies include surgical excision, pulsed laser, and sclerotherapy, which are invasive, with risks of recurrence. There are growing pharmacological options for these vascular anomalies, but, to date, no specific targeted therapies have been developed. Phosphoinositide 3-kinases (PI3Ks) constitute a family of lipid kinases that are involved in signal transduction and vesicular traffic, and that modulate important cellular processes such as proliferation, growth, and migration. Recent findings have indicated that the PI3K signalling pathway is important in the pathogenesis of vascular anomalies. This provides an opportunity to use PI3K inhibitors, which are in clinical trials for cancer treatment, for such lesions. Here, we provide an update on the classification of vascular anomalies, with their major features, and discuss the role of the PI3K signalling pathway in the pathogenesis of vascular anomalies, and their clinical implications and therapeutic opportunities. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Clinical and sonographic features of pediatric soft-tissue vascular anomalies part 2: vascular malformations.

Vascular malformations are a heterogeneous group of entities, many of which present in the pediatric age group. Sonography plays a major role in the management of children with these vascular anomalies by providing information that helps in diagnosing them, in assessing lesion extent and complications, and in monitoring response to therapy. The interpretation of sonographic findings requires correlation with clinical findings, some of which can be easily obtained at the time of scanning. This has to be combined with the use of appropriate nomenclature and the most updated classification in order to categorize these patients into the appropriate management pathway. Some vascular malformations are part of combined vascular anomalies or are associated with syndromes that include other disorders, frequently limb overgrowth, and these are now being reclassified based on their underlying genetic mutation. Sonography has limitations in the evaluation of some vascular malformations and in these cases MR imaging might be considered the imaging modality of choice, particularly for lesions that are large, that involve multiple compartments or are associated with other soft-tissue and bone abnormalities. In this article, which is part 2 of a two-part series, the authors review the most relevant clinical and sonographic features of arteriovenous, capillary, venous and lymphatic malformations as well as vascular malformations that are part of more complex conditions or associated with syndromes, including Parkes-Weber syndrome, phosphatase and tensin homologue (PTEN) hamartoma tumor syndromes, Klippel-Trénaunay syndrome, CLOVES (congenital lipomatous overgrowth, vascular malformations, epidermal nevi and skeletal anomalies) syndrome, fibro-adipose vascular anomaly and Proteus syndrome.

A Diagnostic Program of Vascular Tumor and Vascular Malformations in Children According to Modern Classification.

The aim of the study was to analyze the cohort of inpatient children with vascular anomalies according to the globally accepted classification introduced by the ISSVA. METHODS: The study included 205 inpatient children within the time period of the years 2010-2015. Types of vascular anomalies (VAs), age of patients, diagnostic procedures, and anatomical localization of VAs were analyzed. RESULTS: 65 patients of first year of life had vascular tumors, with prevalence of infantile hemangiomas (IHs) in 57 (87.7%) patients. 45 children had IHs localized within soft tissues, whereas 7 patients suffered from IHs of the liver, and 5 children from IHs of the respiratory tract. Most patients with soft tissue IHs were diagnosed only with ultrasound; СT or MRI diagnostics were performed on 5 (8.8%) patients, and biopsy was carried out in 2 (4.4%) children. Vascular malformations (VM) were diagnosed in 140 (68.3%) patients. Ultrasound investigation (US) was the screening method. MRI was performed to confirm the diagnosis of low-flow VM, whereas for high-flow VM CT angiography and selective angiography were useful. Venous malformations were diagnosed in 17 (12.1%) patients, and 112 (80.0%) had cystic LM, among them children under the age of 2 years prevailed. Arteriovenous malformations were diagnosed in 5 (3.8%) patients, ages 2-14 years. CONCLUSIONS: Clinical manifestations of vascular anomalies have clear age features. Among hospitalized children vascular tumors add up to 31.7% and VM - up to 68.3%.

Klippel-Trenaunay syndrome belongs to the PIK3CA-related overgrowth spectrum (PROS).

Klippel-Trenaunay syndrome (KTS), originally described as a triad of cutaneous capillary malformation, bone and soft-tissue hypertrophy, as well as venous and lymphatic malformations, has been considered by dermatologists as a distinct diagnostic entity. However, cases with KTS have also been reported to have neurological disorders, developmental delay and digital abnormalities, indicating multisystem involvement. Recently, a number of overgrowth syndromes, with overlapping phenotypic features with KTS, have been identified; these include MCAP and CLOVES syndromes as well as fibroadipose hyperplasia. These conditions harbour mutations in the PIK3CA gene, and they have been included in the PIK3CA-related overgrowth spectrum (PROS). Based on recent demonstrations of PIK3CA mutations also in KTS, it appears that, rather than being a distinct diagnostic entity, KTS belongs to PROS. These observations have potential diagnostic and therapeutic implications for KTS.

Treatment Strategy for Persistent Sciatic Artery and Novel Classification Reflecting Anatomic Status.

BACKGROUND: Persistent sciatic artery (PSA) is a relatively rare congenital variant of the lower limb vasculature and can have highly variable clinical presentations. The purpose of this study was to analyze the relationship between PSA anatomy and clinical presentation, and to suggest an optimal management strategy. METHODS: Between 2001 and 2014, 24 PSAs in 19 patients were diagnosed by computed tomography and referred to the vascular surgery department. Patient demographics, types of PSA and femoral artery, aneurysmal changes, symptoms, and treatment methods were assessed. Additionally, all English literature from 1964 to 2014 was reviewed and compared using the PubMed database (224 PSAs in 171 patients). RESULTS: PSA was diagnosed in 10 men (52.6%) and nine women (47.4%). PSAs were bilateral in five patients (26.3%) and symptomatic in 12 patients, while in seven patients PSA was found incidentally. According to the Pillet-Gauffre classification, Type 2a was the most common variant (n = 15/24, 62.5%), with unclassifiable types in two limbs. Compared with cases in the literature, the PSA occlusion rate in this study was higher (n = 10/24, 41.7% vs. n = 54/224, 27.5%), but aneurysm incidence was higher in the literature cases (n = 5/24, 20.8% vs. n = 112/224; 50.7%). In this study, 16 limbs (66.6%) were treated conservatively, and six limbs were treated by open surgery, including four bypasses, one amputation, and one thrombo-embolectomy. Endovascular coil embolization was performed in one limb, and a hybrid procedure with stent graft was performed in one limb with PSA aneurysm. Based on the present series and the literature review, a new classification system and treatment option is proposed according to the anatomic status and the presence of aneurysm. According to the new classification, class III was the most common in both the present study (18/24; 75%) and the literature review, and the presence of aneurysm was the most important determinant of surgical treatment. CONCLUSIONS: The new classification system is simple and provides guidance for management. Limb anatomy of the femoral artery system and the presence of PSA aneurysm should be considered when selecting the optimal treatment. The risk of embolism from the presence of aneurysm is an important factor for treatment, and bypass surgery is mostly required in classes III and IV.

2014 Revised Classification of Vascular Lesions from the International Society for the Study of Vascular Anomalies: Radiologic-Pathologic Update.

Since the publication of the seminal work on the histology-based classification of vascular anomalies by Mulliken and Glowacki in 1982 and the subsequent adoption of an expanded and modified version in 1996 by the International Society for the Study of Vascular Anomalies, an increasing number of vascular lesions have been recognized as histologically distinct entities. Furthermore, there have been significant advances in detailing the behavior and underlying genetics of previously identified lesions. These developments have required restructuring and expansion of the classification scheme so that appropriate therapies may be studied and implemented in affected patients. The new classification retains the broad categories of neoplasms and malformations but now divides the tumor group into benign, locally aggressive or borderline, and malignant, with the malformation group being divided into simple, combined, those of major named vessels, and those associated with other anomalies. Additionally, a category has been created for lesions in which the histology and behavior do not yet allow clear separation into neoplasm or malformation (thus named "provisionally unclassified vascular anomalies"). The known clinical courses and imaging, histologic, and genetic findings of the most common and/or clinically relevant lesions in the newly adopted revised system are reviewed in this article. (©)RSNA, 2016.