Diagnosis of venous disease with duplex ultrasound

Background

One-third of the adult population in the Western world is affected by venous disease (VD). ¹ Most patients with VD have reflux, obstruction or the combination of both while other pathologies such as aneurysms, malformations and tumours are uncommon. The most common pathology in patients with chronic venous disease is reflux, followed by a combination of reflux and obstruction while the latter is rare. ²

The advent of duplex ultrasound (DU) has substantially changed the diagnosis of VD. DU advantages include non-invasive evaluation of venous anatomy, valve function and obstruction in realtime, low cost, portability, safety and repeatability. ³ DU is unable to give an overall value for the condition of the extremity, identify the functional effect of the obstruction and evaluate the efficiency of calf muscle pump. However, it allows accurate diagnosis, instigation of treatment, guide interventions and evaluate the outcome.

Evaluation of venous reflux

Reflux is most often found in the superficial veins with the saphenous veins and their tributaries being the most common location. ⁴ Careful assessment of the distribution and extent of reflux is critical to tailor the treatment to the patient's needs.

The investigation of reflux is performed with the patient in standing position to allow maximum venous distension. Recently, a multicentre study has shown that reflux measurements in the superficial veins were more repeatable when performed in the morning with the patient standing. ⁵ Whenever the patient is unable to be in a standing position, a semierect position or with torso elevation at 45° is recommended.

Reflux may occur in patients with primary venous disease, after an episode of venous thrombosis, secondary to a traumatic or iatrogenic arteriovenous fistula or, rarely, due to congenital malformations including valve hypoplasia or agenesis. It has been defined as abnormal when the retrograde flow lasts > 1000 ms in the common femoral, femoral and popliteal veins and >500 ms for all other veins in the lower extremity.^6,7 Abnormal perforating veins (PVs) are defined as those with an outward flow of duration of > 500 ms, with a diameter of >3.5 mm. ⁷

Manual cuff compression or automated pneumatic cuff inflation/deflation device are used to assess reflux. ⁷ Recently, a multicentre study compared the automated compression/decompression device to manual compression. No significant difference in the duration of reflux was found when those two modalities were compared against each other. ⁵ However, the automated compression/decompression device may be of assistance if comparitive data on the duration of the reflux before and after a venous procedure are warranted. The Valsalva manoeuvre is used to test only the competency of the common femoral vein and sapheno-femoral junction (SFJ).

The diameter of the saphenous trunks and routes of reflux must be obtained. Varicose veins are defined as veins that are >3 mm in diameter having at least two dilations in continuity.^7,8 Dilations of only the valve sinus or of a short segment (<2 cm in length) must not be considered varicosities. ⁸ The saphenous trunks rarely are varicose but often have focal dilations. Vein aneurysm has been defined as vein enlargement of >3 times of the adjacent normal diameter. ⁸ However, no significant work has been done to differentiate vein aneurysms from varicose veins in patients with chronic venous disease (CVD).

The patterns and types of reflux must be recorded. Routinely reflux is first evaluated in the great saphenous vein (GSV) and small saphenous vein (SSV) and their tributaries. The perforating veins are then investigated along the saphenous veins and their tributaries. Evaluation of the deep vein reflux is critical to complete assessment of venous reflux particularly in patients with oedema and skin damage. Primary axial reflux in the deep veins alone is rare. ⁴ Very often segmental reflux is found in the common femoral and popliteal veins, which is caused by a longstanding saphenous reflux involving their junctions. ⁹ Such deep reflux is eliminated after treating the saphenous veins. This is different from the axial deep reflux often found after deep vein thrombosis. Precise determination of deep vein reflux is critical in order to set realistic expectations for the patients and provide proper management. ⁷

Recurrent varicose veins reflux

Reflux is frequently found after treatment. This can be residual or recurrent reflux. Its incidence varies according to the time of the follow-up and method of treatment. ¹⁰ Patients who had SFJ ligation or ablation may present with reflux at the GSV stump level due to tributaries that are connected to the stump or CFV as residual veins.^10,11 Tiny vessels with no valves may also be demonstrated causing reflux at the groin level after GSV ligation (neovascularization).^10,11 An analysis of 170 limbs from the REVAS study participants was performed to assess their presentation, causes and predisposing factors. ¹⁰ Most patients were symptomatic and three-quarters of the limbs had perforator reflux. Notably, reflux was mostly found in the SFJ (47.2%) and leg perforators (54.7%) areas. Another prospective study of patient with recurrent varicose veins after surgery demonstrated that reflux is located at the saphenofemoral or saphenopopliteal junction in at least a quarter of limbs scanned. ¹² A progressive valve function deterioration of the perforators was also shown. ¹²

A standard DU investigation and reporting of residual and recurrent disease after treatment was proposed by an UIP document. ¹³ Morphological and functional characteristics were listed to report findings after surgical, thermal and chemical ablation. A good record of the pretreatment reflux distribution and extent and the procedure notes was emphasized in order to give an accurate account of the post-treatment disease.

Evaluation of venous obstruction

Venous obstruction can be acute and chronic and it is caused from intraluminal and extraluminal pathology or a combination of both. Extrinsic compression can be caused by arteries, tumours, haematomas, cysts, aneurysms and musculoskeletal structures. The most common cause of obstruction is venous thrombosis. DU is the first imaging study utilized to rule out deep vein thrombosis with a sensitivity and specificity of >95%. ¹⁴

Four pertinent components must be obtained while performing a DU, visualization, compressibility, flow and augmentation. ⁷ Compressibility test must be performed every 3–5 cm. It is the most reliable assessment for obstruction and is carried out with the probe in transverse direction in all the deep veins of the extremity including the femoral, deep femoral, popliteal, peroneal, soleal, gastrocnemial and posterior tibial veins. The anterior tibial veins are not routinely scanned due to their low incidence of thrombosis unless local symptoms or history of trauma to the anterior compartment is present. The venous flow must be phasic with respiration especially in central veins and augmented with distal compression or stopped with Valsalva manoeuvre at the level of the common femoral vein. Continuous flow in the common femoral vein having low or no augmentation by any manoeuvres is abnormal and requires an investigation of the iliac veins and vena cava to rule out venous outflow obstruction. A unilateral obstruction of the iliac veins can be demonstrated by asymmetrical common femoral vein flow compared with the normal phasic flow in the contralateral side. It is important to note that the presence of a phasic flow does not exclude obstruction.

Patients with acute deep venous thrombosis (DVT) have dilated veins filled with a hypoechoic, homogeneous, partially compressible thrombus (Table 1). Despite absence of confirmatory DU findings of acute DVT, some patients with high clinical probability measured by a validated score (Wells' score) should be re-imaged in a few days to confirm or exclude acute DVT. Chronic vein changes is suggested when a non-dilated vein with a contracted, organized, hyperechoic, heterogeneous, uncompressible thrombus, firmly adherent to the vein wall is found (Table 1). The term subacute DVT is also used in clinical practice and it illustrates a venous thrombosis event that occurred few weeks to months prior to the duplex scanning. A mixed pattern of hypo and hyperechoic thrombus with or without signs of recanalization or wall thickening is often visualized. Such patients are treated according to their clinical presentation and DU findings. Typically most of these patients are placed on anticoagulation.

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Table 1

DU criteria to distinguish acute from chronic deep vein thrombosis ^*

	Acute (days to weeks)	Subacute (weeks to months)	Chronic (months to years)
Size	Distended	No longer distended due to lysis	Reduced; sometimes unable to be traced by DUS
Echogenicity	Echolucent acute thrombi containing spongy material	Moderate echogenecity. Increased cellular components showing spongy and somewhat organized thrombus	Echogenic: due to fibroblasts and collagen deposits in the thrombus
Lumen characteristics The lumen is non- or partially compressible and often has spongy feel on compression	Recanalization with adherence of residual thrombus to vein wall	Partial recanalization with filling defects (multiple reflux channels) and reflux may be present
Wall characteristics	Thin and smooth	Thickened	Thickening with luminal reduction due to inflammatory response from the thrombus
Flow pattern	Absence of flow/fillings defects	Partial recanalization	Partial recanalization with reflux
Enhanced flow in dilated collateral veins
Thrombus characteristic	Presence of tail	Decreased linear extension of thrombus
Collateral veins	Absent	May be present	Often found around the obstructed segments

DU, duplex ultrasound; DUS, duplex ultrasonography

*

Chronic thrombosis refers to chronic luminal changes, as at a longer stage if the thrombus does not lyse becomes fibrous tissue

Venous stenosis is diagnosed by DU using planimetric measurements of luminal reduction, a poststenotic/prestenotic velocity ratio (V2/V1) of >2.5 slow flow, spontaneous echogenity and vein dilation prior to the stenosis and the presence of collateral veins bypassing the obstruction. ¹⁵ Whenever central vein stenosis or occlusion is suspected other imaging modalities such as magnetic resonance venography, computed tomography venography (CTV) or contrast venography are often used due to the lack of DU training in these areas. Evaluation of obstruction with DU is mostly anatomical providing also some functional information but it is unable to determine its severity.

Recurrent deep vein thrombosis

Many patients with DVT will present with more than one episode that may occur in a previous affected venous segments (acute on chronic) or in a new location, i.e. the contralateral limb. Risk factors for recurrent DVT are previous ipsilateral DVT, age > 65 years, high levels of d-dimer, residual thrombus or previous iliofemoral involvement. ¹⁶ Suggested diagnostic criteria for recurrent DVT are the extension of the thrombus, non-compressibility of a vein segment that had previously been compressible or had previously recanalized and increase in the thrombus thickness by 4 mm.

Superficial vein thrombosis

Most often superficial vein thrombosis (SVT) affects the saphenous veins and their tributaries but it can affect any superficial vein. SVT is not a benign entity as previously thought. Using DU it is critical to determine the extent of SVT because propagation can occur from GSV into the common femoral vein, SSV into the popliteal vein or even causing DVT via propagation through perforating veins. Clinical exam is often inaccurate and underestimates the proximal extension of the thrombus by 5–10 cm. It is of clinical relevance to perform DU to confirm the diagnosis, define the extent of thrombosis and provide data for follow-up.

Conclusion

DU is the method of choice for detecting acute venous disease and CVD, delineating and guiding the treatment as well as evaluating the outcome of interventions. In the investigation of the lower extremity veins the major limitation is the lack of formal training and standardized examination protocols, which could allow to maximize the benefits of using such technology.