We will only describe the most common lesions and those associated with clinical or specific nosological entities.

VMs represent the most common peripheral vascular malformation [43, 44]. They can be simple, combined (e.g., capillary-venous and capillary-lymphaticovenous malformations), or syndromic (associated with Klippel-Trenaunay syndrome, blue rubber bleb nevus syndrome, or Maffucci syndrome). They are present at birth, but patients usually develop symptoms during late childhood or early adulthood (especially during puberty and pregnancy). They vary in size and shape and can be localized and well defined or diffuse and infiltrative. They can involve the superficial and/or deep tissues. When superficial, patients typically demonstrate bluish skin abnormalities and a soft compressible and nonpulsatile soft tissue mass [45]. They typically expand during the Valsalva maneuver and decompress with extremity elevation and local compression [17, 45]. They can also be deep, involving many anatomical structures, including the muscle, synovial membrane, bone, and liver [4, 45, 46]. They may cause pain, impaired mobility, and skeletal deformities. They are usually located on the extremities (40 %), head and neck (40 %), and trunk (20 %) [17, 45]. Elevated D-dimer levels are a specific biomarker for VMs [47].

Pathologically, VMs are characterized by small- or large-sized venous channels connected with the normal venous system. They may contain thrombi whose dystrophic mineralization produces phleboliths [43]. Although pathologists now apply the new ISSVA nomenclature [46, 48], the historical terminology is kept in the current WHO classification (Table 16.1) [5]. Therefore, entities such as cavernous, venous, or intramuscular hemangiomas usually correspond to venous malformations and are still frequently used in pathologic reports using the WHO classification [5, 38, 46].

Phleboliths and dystrophic calcifications are easily detected on radiographs and CT and are highly suggestive of VMs (Fig. 16.8) [2]. In case of extensive malformations, the involvement of the adjacent joints or bones is possible, such as cortical erosion, periosteal reaction, regional osteopenia, and bony overgrowth [49, 50].

Ultrasound shows an extremely variable appearance of the lesion, ranging from predominantly solid to multicystic lesions [1]. VMs can be well defined or infiltrative. These usually hypoechoic and heterogeneous lesions consist of tubular vascular or cavity compressible areas, reflecting the presence of vessels. The phleboliths are usually seen as hyperechoic foci. After applying compression, the movement of blood into the cavities can be identified (Fig. 16.9). Doppler US typically shows no flow or low-velocity flow. In the absence of a spontaneous vascular signal, dynamic maneuvers such as the Valsalva maneuver or manual compression by the probe followed by its decompression can cause the appearance of vascular signal although thrombosis is possible.

MRI is an excellent imaging modality to define the extent of the lesions and their relationship with the adjacent structures. VMs demonstrate well- or ill-defined limits, but they typically do not produce any significant soft tissue mass syndrome, which suggests diagnosis. Vascular vessels are seen as tubular and serpiginous cavities with hypo- to iso-signal intensity on T1-weighted images and strong hyper-signal intensity on T2-weighted images, separated by hyperechoic fat (Fig. 16.10). Fat-suppressed T2-weighted images are particularly useful to evaluate the extent of the VMs. Phleboliths appear as small low-signal-intensity foci on all pulse sequences. Sometimes fluid-fluid levels due to hemorrhage or high protein content can be seen (Fig. 16.11) [1], though they are less common compared to lymphatic malformations. Contrast-enhanced 3-D acquisitions after dynamic gadolinium administration should be performed to evaluate the perfusion of the malformation and its drainage into the venous system. VMs are characterized by a lack of arterial and early venous enhancements and the absence of enlarged feeding vessels or arteriovenous shunting. They typically demonstrate a slow and progressive enhancement. Characteristic nodular enhancement of tortuous vessels can be observed on delayed venous phase images (Fig. 16.12) [3, 51]. The time between the beginning and the maximal enhancement is between 50 and 100 s [52]. Less specific appearances may be encountered when the lesion is composed of small vessels (Fig. 16.13) or in the absence of adipose tissue [53]. Intramuscular VMs often demonstrate serpiginous venous channels between the muscle fibers that are oriented along the long axis of the involved muscle [1]. Intra-articular involvement may lead to chronic hemarthrosis and joint destruction [54, 55] (Fig. 16.14). Localized intravascular coagulopathy is more frequent in diffuse compared to focal VMs and can be responsible for pain and thrombosis [56].

Most VMs are managed conservatively with a compression bandage of the extremity and medical antalgics for pain. In cases of major pain, joint involvement, and functional or cosmetic problems, the first-line treatment for VMs is sclerotherapy (dehydrated ethanol, sodium tetradecyl sulfate, polidocanol, and bleomycin), which can be followed by resection, laser therapy, and photodynamic therapy [57, 58].

LMs represent the second most common type of vascular malformation after venous malformations [59]. These low-flow vascular malformations are classified into three types depending on the size of the cystic cavities [1, 2, 45, 60, 61]:

Pathologically, they are composed of serpiginous dilated lymphatic channels that do not communicate with the normal lymphatic system [45], except in the retroperitoneum. Macrocystic and microcystic lesions are pathologically indistinguishable [61]. Diagnosis is suggested after a positive test for markers of lymph vessels, such as the vascular endothelial growth factor receptor 3 (VEGFR-3), LYVE-1, D2-40, and podoplanin [61–63]. However, it should be kept in mind that LMs can be associated with the other vascular malformations.

LMs are present at birth in half of the patients (prenatal diagnosis of macrocystic types is possible) and are diagnosed before the age of 2 years in 90 % of the cases [61, 64]. They mainly involve the head and neck (55–95 %) and axillary regions (20 %) with a predilection for the left side of the body [64]. They can affect multiple structures (lung, intestine, liver, spleen, etc.) including the bones [38]. Macrocystic LMs are typically large and clinically manifest as a soft swelling mass with a rubbery consistency. They are well limited and mobile under a normal skin [57, 64]. Transillumination confirms the liquid nature of the lesion. The majority of the cases are asymptomatic, but complications, such as local compression, sudden increase in size secondary to bleeding (trauma), or infection from an adjacent process of the head and neck, can occur [65].