Venous malformations (VMs) are characterized by vein wall defects due to vascular dysmorphogenesis caused by the lack of smooth muscle cells. As a result, the veins become enlarged, with impaired blood circulation (1-3). VM is the most common type of congenital vascular malformation (CVM), comprising up to two-thirds of CVMs, with an incidence of 1∼2 in 10,000 and a prevalence of 1% (4,5). Although VM may be present at birth, it is not always clinically evident until later in life (6). The presen-tation varies according to the location and extent of VM the and tissues involved (7). Approximately 40% of VMs occur in the extremities (8). When it affects the lower extremities, the symptoms and signs are similar to those of varicose vein (VV). These symptoms can range from aesthetic issues to chronic venous insufficiency symptoms, and the severity of symptoms is associated with the extent of the disease (7). The extent of VM can vary considerably from being focal to involving most of the extremity. It may also involve one tissue, that is, subcutaneous, or multiple superficial and deep tissues, including the bone. The natural history and prognosis of VVs and VM are different, and the discrimination of both diseases is critical for devising management strategies. This paper focuses on ultrasound imaging of VM to facilitate differential diagnosis and treatment planning.

VM can be clinically diagnosed when it is present at birth or when the lesion shows characteristic morphological features of bluish skin discoloration. Superficial and localized lesions without specific symptoms or signs that indicate treatment may not require imaging studies. In cases of symptomatic or extensive lesions, Doppler ultrasono-graphy (US), computed tomography, and magnetic resonance imaging (MRI) or magnetic resonance venography (MRV) are the preferred methods for the initial diagnosis of VMs and post-treatment follow-up (5). Duplex US is a useful, noninvasive imaging technique and should be used as the first modality when investigating the presence of a VM, especially for superficial lesions or those in the extremities (9). Other benefits of duplex US include its ubiquity in clinical settings, low cost, and lack of ionizing radiation, which is an important aspect in young patients (10). When the area affected with VM is large, US may not be sufficient to evaluate overall lesion progression. Additionally, US has limited ability to display the full extent of large lesions and intraosseous components. MRI or MRV is used when there is a lack of US experience, the quality of the ultrasound image is suboptimal, or the VM is complex or extensive.

1) Ultrasound protocol

Lower-extremity venous duplex examinations are generally performed with a linear array transducer using high frequencies of 9∼12 MHz. Because ultrasound examination of VMs does not document reflux, it can be performed with the patient in the supine position. However, standing or reverse Trendelenburg positioning may facilitate examina-tion by dilating the veins. These positions are also useful when reflux needs to be evaluated, as in patients with Klippel–Trenaunay syndrome, characterized by VM and varicosities. When the lesion is visible superficially, the area around the suspected lesion can be observed. If the lesion is extensive, the deep and superficial veins of the affected limb should be examined. Sonographic techniques include a combination of grayscale, color Doppler, and spectral wave Doppler examinations. Once the echotexture, borders, and size of the lesion are measured with gray-scale imaging, color Doppler and spectral wave Doppler examinations are performed to document the flow characteristics within the lesion. When VM is associated with Klippel–Trenaunay syndrome or other phosphatidy-linositol 4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA)-related overgrowth syndromes, marginal veins can be observed from the lateral aspect of the leg. The marginal vein is a valveless anomalous vein that charac-teristically lacks fascial encasements (11). It needs to be differentiated from the persistent sciatic vein (PSV), which is a lower-extremity persistent embryonic vein (12). The PSV is situated deep in the thigh and originates from tributaries that emanate from the popliteal vein. It follows, in part, the sciatic nerve and connects the gluteal perforators with the internal iliac venous system. VM can be found at different locations in patients with such syndromes, and Doppler ultrasound can help detect the VMs and demonstrate their extent and tissue involvement.

2) Characteristics of VM on ultrasound imaging

The margin and size of the lesion can be measured on gray-scale examination. Appearances of the lesions range from purely solid to multicystic and localized and from well-defined to infiltrative or cavitary (most common) dysplastic (5). VM appears hypoechoic or heterogeneous in 80% of cases (13,14). When VM is not associated with thrombosis, it is compressible. It should be noted that some VMs are harder to compress; therefore, more pressure should be applied to the transducer. The detection of phleboliths with acoustic shadowing further supports the diagnosis because these are rare in other soft tissue tumors (15,16). Anechoic channels can be visualized in less than 50% of cases. Occasionally, isoechoic thickening of the subcutaneous tissue without a solid mass or discernible channels is the only feature. Hypoechoic foci with posterior acoustic shadowing were observed in less than 20% of cases. All previous treatments should be noted, as imaging after treatment may show different characteristics based on the method used. Doppler ultrasound can confirm slow flow or absence of flow within the malformation. Occasionally, flow may be observed only when performing the Valsalva maneuver or distal augmentation (17). In cases where no flow is produced with distal augmentation, direct com-pression with the transducer over the VM should be performed to demonstrate the flow. This is often seen because the flow in many VMs is extremely slow. Furthermore, in many patients, the flow in the VMs produces spontaneous contrast, mimicking the image of a very fresh thrombus. In such cases, adequate compression should be applied by the transducer to ensure that there are no thrombi in the VM. A clinical case is presented below to demonstrate some of the imaging characteristics of VMs.

3) Clinical cases with ultrasound images

Experience is required to image VMs in order to accurately diagnose and provide all measurements necessary to guide treatment. If the ultrasound report is inadequate or incomplete, an MRI/MRV examination should be performed. The person who performs the imaging should be familiar with any potential limitations related to his/her experience and those of ultrasound. Some cases that may be helpful for physical examination and ultrasound assessment are also presented.

(1) Case 1

A 33-year-old woman presented with a long-standing history of a large mass on the right lateral foot with increased swelling and pain on palpation (Fig. 1). She had a history of occasional pain with palpation or ambulation, particularly with prolonged standing, and no history of venous thrombosis or trauma. She underwent sclerotherapy for the mass in 2000. Ultrasound B-mode imaging revealed multiple dilated veins on the lateral aspect of the foot (Fig. 2A). The lesion extended from behind the lateral malleolus to the base of the toe. The diameters of the veins varied from 1 to 6 mm. On color flow imaging, slow flow was observed in multiple veins and the flow was augmented by distal compression (Fig. 2B). Spectral Doppler waveform also revealed slow flow (Fig. 2C).

Fig. 1. A mass on the lateral aspect of the right foot. This patient presented with a long-standing history of a large mass on the right lateral foot with increased swelling and pain on palpation.

Fig. 2. Ultrasound imaging of the foot mass. (A) B-mode imaging. Multiple dilated veins were found in the lateral aspect of the foot. (B) Color flow imaging. Slow flow is seen in multiple veins. PRF was set at 750 Hz in order to demon-strate the slow flow. The flow was augmented by distal compression (right panel). (C) Pulse-wave Doppler Imaging. Slow venous flow is observed. The waveform does not contain arterial components.

On MR, a large, complex, low-flow VM along the lateral aspect of the ankle and foot was observed, which insinuated within the intermuscular fat of the flexor compartment (Fig. 3). The lesions were markedly hyperintense on the T2- weighted images.

Fig. 3. Magnetic resonance image of the right foot. A large, complex, and low-flow venous malformation is observed along the lateral aspect of the ankle and foot, insinuating within the intermuscular fat of the flexor compartment.

(2) Case 2

Other imaging features of VM can be observed in images obtained from various patients. Fig. 4 shows an anterior shin mass in a 56-year-old man (Fig. 4A). This patient had a hard mass that had not regressed or increased in size for many years. Ultrasound B-mode imaging showed multiple dilated veins in the subcutaneous space (Fig. 4B-D). No spontaneous flow was observed on color flow imaging (Fig. 4E).

Fig. 4. Ultrasound imaging of the shin mass. (A) Gross image of the shin mass. This patient presented with a mass on the anterior shin that was hard to the touch. (B-D) B-mode images. Dilated veins in the subcutaneous space appear as multiple hypoechoic tubular lesions. (E) Color mode image. There is no spontaneous flow in the lumen.

(3) Case 3

Fig. 5 shows anterior and anterolateral thigh VMs. A 39-year-old man presented with a dilated vein in the thigh and symptoms of swelling and pain (Fig. 5A). Ultrasound B-mode imaging showed multiple dilated veins in numerous locations of the subcutaneous and intramuscular spaces (Fig. 5B-D). On color flow imaging, short reflux was seen in multiple veins using distal compression with sudden release (Fig. 5E). On spectral Doppler imaging, slow flow was observed (Fig. 5F), which was augmented with low intensity by forceful distal compression (Fig. 5G).

Fig. 5. Thigh VM. (A) Gross image of the patient. Lateral thigh VM is observed. (B-D) B-mode imaging. Dilated veins are observed in subcutaneous and intramuscular spaces. (E) Color flow imaging. Flow was observed in the intramuscular dilated vein on distal compression. (F, G) Spectral Doppler imaging. Very slow flow was observed within the dilated vein, and short low-intensity reflux was observed with forceful distal compression. VM: venous malformation.

4) Differential diagnosis with VV

Table 1 summarizes the differences between VM and VV. First, the etiologies of the two diseases are different. VM is congenital and usually occurs at birth. In some cases, where VM is not recognized at birth, it often presents as a mass that does not regress on its own for many years. VM can occur anywhere in the body. VV is caused by reflux in the lower extremities and appears relatively late in life. Both types of disease can appear as dilated hypoechoic tubular structures on B-mode imaging; however, VM can be found at various depths, including subcutaneous, intramuscular, or even within the bone. VMs exhibit much slower flow than VVs. Reflux can be observed in VMs. However, even if reflux is found in a VM, the intensity is low, and the duration is short, unlike the reflux seen in VVs.

Table 1

Differential diagnosis of venous malformation (VM) and varicose vein (VV)

	VM	VV
Cause	Birth defect	Reflux
Presentation	At birth	Various
Location	Various	Lower extremity
Shape	Dilated vein	Dilated vein
Extent	Localized, extensive	Localized, extensive
Flow	Stagnant flow	Normal venous flow
Reflux	Low intensity	>0.5 sec
	Short duration

Ultrasonography is an excellent method for the diagnosis and follow-up of patients with VM. The imaging features of VM are distinct and easy to recognize using ultrasound. Experience is necessary to understand most VM patterns and provide an accurate diagnosis to help plan treatment. When there is limited experience with ultrasound or the exam is inadequate, and in cases with extensive complex VMs, MRI/MRV should be performed.