Internet Book of Musculoskeletal Ultrasound » Deep Vein Thrombosis

Deep Vein Thrombosis

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Authors

Yvonne Chow, MD, CAQ-SM
Albany Medical Center

Summary

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Illustration of Deep Vein Thrombosis

Introduction

Deep venous thrombosis (DVT) is clinically important because of the potential morbidity caused by acute pain as well as long term damage to the veins that can result in impaired venous return, leading to chronic pain, swelling and skin changes associated with venous stasis.
Even more concerning is the potential for a DVT to propagate centrally into the pulmonary circulation, occluding the pulmonary arteries and causing a Pulmonary Embolism (PE).
The annual incidence of DVT alone in the US is about 370,000 and with the addition of PE well above 600, 000^[1]Heit JA, Cohen AT, A F. Anderson, on Behalf of the VTE Impact Assessment Group; Estimated Annual Number of Incident and Recurrent, Non-Fatal and Fatal Venous Thromboembolism (VTE) Events in the US. … Continue reading.
It has generally been estimated that approximately 90% of PEs originate from a lower extremity DVT, and about 1/3 of untreated DVTs can progress to a significant PE^[2]Calder KK, Herbert M, Henderson SO. The mortality of untreated pulmonary embolism in emergency department patients. Ann Emerg Med. 2005;45(3):302-310..
PE carries a 30 day mortality rate somewhere between 10 to 30%, with at least 20% of these presenting as sudden cardiac death^[3]Beckman MG, Hooper WC, Critchley SE, Ortel TL. Venous thromboembolism: a public health concern. Am J Prev Med. 2010;38(4 Suppl):S495-501..

A DVT is an important diagnosis to make so that treatment with anticoagulants can be initiated promptly.
In the past, venography was the gold standard for DVT diagnosis. However, it is invasive, costly and poses risks such as contrast reaction and postvenographic phlebitis.

Ultrasound video showing normal vein and a fantastic view of the valvees.

Over time, duplex Doppler ultrasound has become the standard imaging for diagnosing acute lower extremity DVT. These studies are typically performed by a vascular technician or sonographer, and often times include evaluation of the deep veins of the entire leg including calf veins. Many studies have shown that clinical providers can also accurately perform DVT ultrasound with appropriate training.
It is important to point out that there are a few different protocols used by point-of-care ultrasonographers that may yield different sensitivities.
POCUS allows for making clinical decisions about DVT treatment especially where sonographers are not readily available, and can significantly decrease ED disposition time by at least 2 hours^[4]Theodoro D, Blaivas M, Duggal S, Snyder G, Lucas M. Real-time B-mode ultrasound in the ED saves time in the diagnosis of deep vein thrombosis (DVT). Am J Emerg Med. 2004;22(3):197-200..

Commonly Used Scanning Protocols

2-point limited compression technique
- Some providers use a 2-point limited compression technique where two regions are interrogated: the common femoral vein in the groin, and the popliteal vein in the popliteal region.
3-point limited compression technique:
- Others use a 3-point limited compression technique where the common femoral vein is viewed in the groin, and then interrogation continued to the very proximal thigh where the common femoral vein splits into the femoral veins (deep and superficial), and then jump to behind the knee to catch the popliteal vein.
- Emergency physicians performing limited compression ultrasound is highly accurate, with one pooled estimate demonstrating a sensitivity of 90% and a specificity of 95%^[5]Lee JH, Lee SH, Yun SJ. Comparison of 2-point and 3-point point-of-care ultrasound techniques for deep vein thrombosis at the emergency department: A meta-analysis: A meta-analysis. Medicine … Continue reading.
Extended compression ultrasound:
- Many emergency medicine physicians perform an extended compression ultrasound which typically consists of examining the majority of the upper leg from the common femoral vein in the groin through the (superficial) femoral vein in the thigh down to just proximal to the knee, and the popliteal vein in the popliteal fossa until it trifurcates into the tibial veins. Extended compression ultrasound is preferred over 2- or 3-point limited compression because it can detect the 5-7 % of DVTs that can be isolated to the (superficial) femoral vein in the distal thigh, thereby increasing the sensitivity of the exam^[6]Needleman L, Cronan JJ, Lilly MP, Merli GJ, Adhikari S, Hertzberg BS. Ultrasound for lower extremity deep venous thrombosis: Multidisciplinary recommendations from the society of radiologists in … Continue reading^[7]Adhikari S, Zeger W, Thom C, Fields JM. Isolated deep venous thrombosis: Implications for 2-point compression ultrasonography of the lower extremity. Ann Emerg Med. 2015;66(3):262-266..
- These protocols forego evaluating for clots isolated to the calf, because these are unlikely to embolize centrally. Furthermore, treatment of these isolated distal calf veins is debatable.

Ultrasound Probe and Setup

The veins of the lower extremity are usually superficial and warrant the higher frequency of a linear probe (5 to 10 MHz). However, if the patient is obese, you may want the deeper penetration of a curvilinear probe (3.5 to 6.5 MHz).
Common ultrasound presets that can be used include the vascular or superficial settings.

The exam is typically done with the patient supine in the “frog leg” position with the leg abducted and rotated externally, and the knee slightly flexed.
For the popliteal veins, the patient can stay in the frog leg/supine position. However, if adequate images are not obtained, the patient may be placed in the prone position.
Lateral decubitus positioning can be used to help visualize the calf veins.
A reverse Trendelenburg tilt to the examination bed or having the patient sit can distend the calf veins, aiding in vein identification.

Linear transducer typically used in VTE evaluation

Demonstration of the frog leg position

Demonstration of the prone position

Demonstration of the lateral decubitus position

Demonstration of reverse trendelenburg

Anatomy

The venous system of the lower extremities consists of smaller veins in the distal leg that drain blood into larger veins in the proximal leg, before eventually dumping into the iliac veins and inferior vena cava in the abdominal cavity.
The deep veins of the proximal leg always run with an artery.
Duplication of the femoral and popliteal veins is seen in up to 20% and 35% of patients, respectively. This anatomic variant is important to keep in mind when searching for clot.8

Illustration of the veins of the lower leg (click to enlarge)

There are four anatomy regions that can be included in your ultrasound:
- Inguinal fold: common femoral vein, artery
- Proximal thigh: greater saphenous vein, superficial femoral vein
- Popliteal fossa: popliteal artery, vein
- Lower leg, calf: tibial veins
At the level of the inguinal ligament, the common femoral vein and common femoral artery course next to each other, extending from the external iliac vein and artery respectively.
- The greater saphenous vein (GSV) enters the common femoral vein medially at the level of the groin, just inferior to the inguinal ligament
- The GSV is actually a superficial vein, but at the level of the groin it is a very important part of the venous system because it is right at the entry point of the deep venous system. Any DVT seen at this point has a high chance of propagating into the deep veins, and so warrants treatment
Moving distally, the common femoral vein breaks into the superficial and deep femoral veins.
- The superficial femoral vein is NOT a superficial vein. It is a deep vein, and actually the main vein that is tracked in the leg to look for a DVT. Some textbooks will call the superficial femoral vein the “femoral vein” to prevent confusion.
- The deep femoral vein is smaller and harder to see on ultrasound.
The (superficial) femoral vein moves deeper in the thigh as it courses distally, and eventually runs behind the knee in the popliteal fossa to become the popliteal vein, where it trifurcates into the:
- Anterior tibial vein, with accompanying artery, into the anterior compartment of the calf to the dorsum of the foot.
- Posterior tibial vein, with accompanying artery, travels in the deep musculature of the posterior calf and passes posterior to the medial malleolus.
- Peroneal or fibular vein, with accompanying artery, runs medial to the posterior aspect of the fibula
Gastrocnemius and soleal veins are located within the respective muscles of the calf and do not have accompanying arteries. Some centers do not routinely scan these veins.

Normal Ultrasound Anatomy

This study is accomplished by scanning the deep venous system from the groin down the leg.

Inguinal Fold

Starting in the inguinal fold, you will place the probe in line with the groin crease, in a transverse orientation. The probe indicator should be pointed to the patient’s right regardless of which leg you are scanning.
Once you identify the common femoral vein and artery in the inguinal fold, start scanning about one centimeter above that region, looking for a clot. Then from this point, you should follow the common femoral vein down the leg, compressing the vein every one to two centimeters.

Anatomy illustration of the femoral triangle (click to enlarge)

In the inguinal fold, the common femoral vein is right next to and medial to the common femoral artery. In either leg the common femoral artery is lateral to the vein (often remembered using the acronym NAVEL which stands for nerve, artery, vein, empty space and lymph node which describes the order of structures in the inguinal crease region, starting laterally and moving medially towards the navel in either leg).

Starting probe position

Video of common femoral vein compression

Ultrasound of the greater saphenous vein (SV), common femoral vein (CFV) and common femoral artery (CFA).

Ultrasound of the left common femoral vein with and without compression

Ultrasound of the right mid femoral vein with and without compression.

Ultrasound of the right ionferior femoral vein with and without compression.

Proximal Thigh

The greater saphenous vein enters the common femoral vein medially at the level just inferior to the inguinal crease. It is important to assess the greater saphenous vein for any clot at this level and for about 5cm proximal to its entry into the common femoral vein. If a clot is present, then this is a clinically significant venous clot that must be treated.

Ultrasound of the upper thigh

As you move the probe distally (about 6-8cm below the inguinal ligament), the (superficial) femoral vein will transition to below the femoral artery. As you move more distally, the femoral vein and artery will dive deeper into the adductor canal of the leg.
As the vein gets deeper in the leg you will likely need to increase the depth of the ultrasound field. Continue scanning down the thigh until you reach the knee or until you can no longer see the (superficial) femoral vein.

Popliteal Veins

With the probe nestled in the popliteal fossa behind the knee, still in transverse orientation, the popliteal vein and artery will be vertical to each other, with the popliteal vein on top of the artery (often remembered using the phrase “Pop on Top”).
The popliteal vein will trifurcate into 3 small tibial veins. Sometimes the 3 branches diverge at nearly the same time. Other times, you will see one branch come off one after another.

Ultrasound of the popliteal artery and vein

Popliteal vein trifurcation

Video demonstrating compression of Popliteal vein

Tibial Veins

If you choose to identify the tibial veins more distally into the calf, you can trace them down the leg from the popliteal region to the ankle.
If having difficulty identifying the distal tibial veins, you could try finding the veins just above the ankle and scan retrograde up the calf/leg^[13]Rumack CM, Wilson SR, Charboneau JW, Johnson J-A. Diagnostic Ultrasound. 3rd ed. Mosby; 2004..

Ultrasound of non compressible calf or tibial veins.

Dilated vein in the gastrocnemius in long axis. No DVT is present.

Dilated vein in the gastrocnemius in short axis. No DVT is present.

Pathology

Compressibility of the vein is the main modality for evaluating for deep vein thrombosis.

The deep veins are compressed with the probe, with the expectation that the vein should collapse under adequate pressure. If it does not collapse, then there is concern for something keeping the vein open, specifically a DVT.
Blood clots in the vein are often hyperechogenic and either completely or partially occlude the vein. The clot may also be isoechoic in nature. Unfortunately, sometimes the vein can even be hypoechoic, especially early on in clot formation.

Ultrasound of non compressible common femoral vein with echogenic thrombus

Non compressible popliteal vein with arrow pointing to clot burden (1 of 2).

This is the same patient with the probe sagital over the vein and the clot is easily identified (2 of 2)

To determine whether you have adequate probe pressure for compression of the vein, you should compress the vein until the neighboring artery starts to compress. If you can compress the artery (which is a higher pressure system than a vein) and the vein remains open, then you must presume there is a blood clot in the vein. This is regardless of whether you can visibly see a clot within the vein.

Ultrasound of clot burden

Ultrasound of partially compressed vein

Color and pulse wave doppler can be used as an adjunct to compression of the veins, not in lieu of it. This is often used by vascular lab technicians, and less often by EM physicians.
It is relatively simple to do, however, only a small amount of clinical information is added. Generally, relevant information can be obtained by using just compression of the veins.
The limitations of color or pulse wave spectral doppler is that findings with these modalities may not occur if there is a partially occluded DVT.

Ultrasound of color or pulsewave doppler

Pulse wave doppler ultrasound of a positive DVT study. Note there is no doppler signal on the bottomo of the image which suggests DVT. Also note that you can see the DVT where the indicator is.

Pearls and Pitfalls

A noncompressible vein trumps the absence of a hyperechoic clot in diagnosing a DVT
How much pressure is adequate pressure for compression ultrasound? Apply enough pressure that it causes the neighboring artery to collapse. If the vein is still not compressed, there is concern for a DVT.
If more pressure is needed to collapse the vein, try applying pressure to the posterior aspect of the leg to help minimize the distance of the soft tissue, bringing the vein closer to the probe. Do not apply too much pressure though. Especially in the popliteal region you may need to release the pressure of your probe to be able to see the lumen of the vein.
The deep veins ALWAYS run with an artery. If you see an isolated vein, then this is not a vein in the deep venous system. It is likely you are too superficial and the vein of interest is actually deeper (a common mistake in bigger patients)
The superficial femoral vein is NOT a superficial vein. It is a deep vein, and the main vein we monitor for DVT.
Compression technique is typically all that is needed to perform an adequate DVT study.

Don't Mistake a DVT for the following

Lymph node: this vascular structure has an appearance similar to the kidney with a hypoechoic rim and hyperechoic center, and can be especially noticeable in the proximal thigh.

Ultrasound demonstration of a normal appearing lymph node

Baker’s cyst: this will appear as an irregularly shaped hypoechoic structure in the popliteal fossa. Applying color to this area will reveal there is no flow.

Ultrasound demonstration of Baker’s Cyst

Aneurysm: can make the difference between anticoagulation and a vascular surgery consult. This can be seen in the popliteal artery or the distal aspect of the (superficial) femoral vein. An aneurysm will look like a bulge or focal enlargement of at least 20% of the expected diameter. Color doppler will show a swirling blood flow pattern.

Ultrasound demonstration of popliteal venous aneurysm.

With special thanks to Dr Vi Dinh of pocus101.com for allowing us to use many of his images.

References

References[+]

References
↑1	Heit JA, Cohen AT, A F. Anderson, on Behalf of the VTE Impact Assessment Group; Estimated Annual Number of Incident and Recurrent, Non-Fatal and Fatal Venous Thromboembolism (VTE) Events in the US. Blood. 2005;106(11):910.
↑2	Calder KK, Herbert M, Henderson SO. The mortality of untreated pulmonary embolism in emergency department patients. Ann Emerg Med. 2005;45(3):302-310.
↑3	Beckman MG, Hooper WC, Critchley SE, Ortel TL. Venous thromboembolism: a public health concern. Am J Prev Med. 2010;38(4 Suppl):S495-501.
↑4	Theodoro D, Blaivas M, Duggal S, Snyder G, Lucas M. Real-time B-mode ultrasound in the ED saves time in the diagnosis of deep vein thrombosis (DVT). Am J Emerg Med. 2004;22(3):197-200.
↑5	Lee JH, Lee SH, Yun SJ. Comparison of 2-point and 3-point point-of-care ultrasound techniques for deep vein thrombosis at the emergency department: A meta-analysis: A meta-analysis. Medicine (Baltimore). 2019;98(22):e15791.
↑6	Needleman L, Cronan JJ, Lilly MP, Merli GJ, Adhikari S, Hertzberg BS. Ultrasound for lower extremity deep venous thrombosis: Multidisciplinary recommendations from the society of radiologists in ultrasound consensus conference. J Vasc Surg Venous Lymphat Disord. 2019;7(2):282.
↑7	Adhikari S, Zeger W, Thom C, Fields JM. Isolated deep venous thrombosis: Implications for 2-point compression ultrasonography of the lower extremity. Ann Emerg Med. 2015;66(3):262-266.
↑8	Image courtesy of Dr Vi Dinh, pocus101.com, “DVT Ultrasound Made Easy: Step-by-Step Guide”.
↑9	Case courtesy of Assoc Prof Craig Hacking, Radiopaedia.org, rID: 70536
↑10, ↑12	Image courtesy of Dr Vi Dinh, pocus101.com, “DVT Ultrasound Made Easy: Step-By-Step Guide”.
↑11	Lee B, Choi YS. Nerve blocks for optimal postoperative analgesia after total knee arthroplasty. Anesth Pain Med. 2019;14(3):249-254.
↑13	Rumack CM, Wilson SR, Charboneau JW, Johnson J-A. Diagnostic Ultrasound. 3rd ed. Mosby; 2004.
↑14	Case courtesy of Dr Ali Abougazia, Radiopaedia.org, rID: 23174
↑15	Kuna, S. K., Bracic, I., Tesic, V., Kuna, K., Herceg, G. H., & Dodig, D. (2006). Ultrasonographic differentiation of benign from malignant neck lymphadenopathy in thyroid cancer. Journal of Ultrasound in Medicine: Official Journal of the American Institute of Ultrasound in Medicine, 25(12), 1531–1537; quiz 1538–1540.
↑16	Emmerich, J., Blachier, V., Fanon, L., Mairesse, S., Cordier, C., & Alsac, J.-M. (2019). Treatment of popliteal venous aneurysms by femoral vein ligation. Journal of Vascular Surgery Cases and Innovative Techniques, 5(3), 228–231.