Venous malformations (VMs) have been described by the Mulliken and Glowacki classification of vascular anomalies in 1982 (1). They are classified as low-flow vascular malformations in opposition to high flow lesions such as arteriovenous malformation and arteriovenous fistula. These malformations are well distinguished from vascular tumors (most often hemangiomas) based on endothelial characteristics, as VMs are composed of normal endothelial-lined vascular spaces without hypercellularity whereas hemangiomas are characterized by several histological abnormalities, including hyperplasia. The Mulliken and Glowacki classification has been revised since its creation, and the ISSVA (International Society for the Study of Vascular Anomalies) classification of vascular anomalies (2) is now used to define vascular anomalies (as shown in Table 1). The revised version of 2018 continues to divide vascular anomalies into vascular tumors and vascular malformations and classifies vascular malformations in simple or combined (if two or more vascular malformations are found in one lesion) rather than high or low flow. Associated syndromes (Klippel-Trenaunay, Blue-rubber bleb nevus, Familial cutaneomucosal venous malformation, Maffucci’s) and specific mutations (TIE2 mutation) have been also included in the classification.
VMs are always present at birth by definition, thus have to be considered as congenital lesions, and grow in parallel with the child's development (3, 4), with a peak from infancy to puberty. VMs may be very small initially and thus be identified only later in childhood or teenagehood(5, 6). Both sexes are equally affected with a reported incidence of 1–2 per 10,000 births and a prevalence of 1% (5, 6).
Clinically, these lesions are superficial, soft, without pulsations, thrill or increase of temperature relative to adjacent skin, in contrast to arteriovenous malformations. The size of the VM can increase with activity, Valsalva, or supine position (5, 7, 8). Classical appearance changes from light to dark-blue lesions.
VMs can sometimes be painful, especially in cases of facial VMs, if the temporal muscle is affected (patients can complain of migraine). Patients could also present with swelling and pain, due to thrombosis of a portion of the lesion (5).
Diagnostic workup should start first with Ultrasonography (US), to identify the classic hypoechoic, heterogeneous and compressible appearance of VMs. Duplex is then used to show the low-flow, and identify the feeding vessels and intralesional thrombosis. Duplex ultrasound is also the best modality to differentiate hemangioma (high flow on duplex) from VMs (low flow). This discrimination is important because in case of misdiagnosis, inappropriate beta-blocker therapy may be proposed(9). MRI T1 and T2-weighted sequences are considered as the gold standard to assess VMs (10, 11). On fat-saturated T2-weighted MR, VMs appears hyperintense, heterogeneous with lobulated margins. Phleboliths are sometimes visible inside the lesion. In selected cases, contrast venogram, CT scan or even scintigraphy could be useful (5).
Treatment options include medications, surgery, sclerotherapy, cryoablation, and laser photocoagulation; the decision for treatment should be ideally done after interdisciplinary discussion. Small well-localized VMs are often treated successfully with a single modality (surgery, sclerotherapy), whereas larger venous malformations may require a combination of technique (3–5, 9).
Compressive therapy is a simple and efficient option mostly for VMs of the extremities to reduce pain and thrombosis; targeted medical treatment consist of low-dose aspirin, anti-inflammatory drugs or low molecular weight heparin in cases of pain associated to thrombophlebitis (12, 13).
The modality of choice for the treatment of VMs is considered to be sclerotherapy, which can be curative, or used prior to surgery as a neo adjuvant solution, mostly to induce thrombosis inside the lesion to facilitate excision (12). Many different sclerosants are available, including alcohols, detergents, antitumor agents and doxycycline. Alcoholic agents considered to be the most effective, with a very low recurrence rate (12), but also associated with an increased risk of lesions for adjacent skin, nerves and soft tissues.
Surgery alone is sometimes preferred to sclerotherapy, especially when the venous malformation is small and does not involve vital structures; the use of sclerotherapy as an neoadjuvant therapy is often advocated mostly to reduce intraoperative blood loss, to decrease the volume of the malformation to be resected and to improve visualization of vital structures.