CME article 9

 

CME: Deep Venous Thrombosis: Recent Trends


 

Deep venous thrombosis (DVT) is a common clinical problem that complicates many medical and surgical disorders. It can cause morbidity in itself due to acute pain and swelling of the affected limb, and it may also cause structural damage to the valves of the deep veins that results in the postphlebitic syndrome. If not recognized, deep venous thrombi can extend and embolize to the pulmonary arterial circulation. Pulmonary embolism can cause sudden death or, if nonfatal, result in shortness of breath and chest discomfort. Antithrombotic therapy reduces the morbidity of this disorder and the risk of it causing pulmonary embolism. However, since the clinical signs and symptoms of DVT are nonspecific, it is important to promptly perform testing to confirm the diagnosis and enable the institution of safe and effective therapy.

 

CLINICAL PRESENTATION 

Patients who come to medical attention because of symptoms of lower extremity DVT will usually present with symptoms of calf-popliteal vein DVT pain and swelling of calf in one leg, associated increased warmth, redness, and tenderness of the calf area, or with symptoms of iliofemoral DVT (symptoms of pain in the buttock and/or groin region). With time, the entire leg may become swollen, painful, and dusky in color, and prominent collateral superficial veins may develop. This syndrome is referred to as phlegmasia cerulea dolens.

 

ETIOLOGY

DVT in the peripartum period frequently occurs in the iliofemoral region, and in over 90% of cases, it will involve the left leg, likely due to compression of the left common iliac vein by the right iliac artery during pregnancy. DVT associated with a pelvic mass or recent pelvic surgery is typically found in the iliofemoral veins. Also, DVT occurring in association with oral contraceptive use or the antiphospholipid antibody syndrome may first develop in the iliofemoral system. The antiphospholipid antibody syndrome is a condition caused by the development of autoantibodies that interact with phospholipid surfaces. DVT usually develops in only one leg at a given time. Bilateral calf popliteal DVT is occasionally seen in patients with metastatic adenocarcinoma. Iliofemoral DVT may result in bilateral findings if the thrombus extends proximally to involve the inferior vena cava.

 

ASYMPTOMATIC DVT

Most patients who develop DVT are asymptomatic. Most patients with postoperative DVT have no specific symptoms, likely because the thrombi are very small (in some cases, <1 cm in length), and they often do not cause vein occlusion. Postoperative thrombi do not necessarily follow the typical anatomic distribution seen in symptomatic patients. Postoperative DVT may involve an isolated portion of one of the proximal leg veins, likely due to local trauma from the surgical procedure, and most resolve spontaneously without causing specific symptoms or complications.

 

PATHOGENESIS AND RISK FACTORS FOR DVT

Many patients who develop DVT have well-defined risk factors that are associated with this condition. These risk factors include recent malignancy, major surgical procedures, trauma, prolonged immobilization, pregnancy or use of oral contraceptives, underlying inflammatory states, or a previous history of venous thromboembolism.

 

DIAGNOSTIC METHODS FOR DVT

 

Clinical Diagnosis

Before the 1970s, the diagnosis of DVT was made entirely on clinical grounds. With the availability of venography, it became recognized that errors were made when the diagnosis of DVT was based on the clinical examination alone.

 

Venography

Ascending venography was the first imaging procedure available for the diagnosis of DVT and has been regarded as the reference-standard technique. Venography remains the only diagnostic test that enables reliable detection of DVT isolated to the calf veins, the iliac veins, or the inferior vena cava. Venography is also the most accurate method for the diagnosis of asymptomatic thrombi. However, it has a number of limitations that make it less practical and attractive than noninvasive methods. In addition to the technical challenges associated with obtaining an adequate venogram, there are both minor and serious adverse side effects associated with this invasive procedure. These include local pain, skin reactions, and postinjection superficial phlebitis. Nausea, vomiting, and dizziness may also occur. Clinically important venous thrombosis after venography has been reported in up to 2% of patients in whom conventional ionic contrast agents were used but is likely to be less common with the use of nonionic contrast medium. Real-time B-mode US provides direct visualization of the deep venous structures and has proved to be the most sensitive and specific noninvasive test for the diagnosis of DVT involving the proximal leg veins.

Ultrasound
Fig 1 (Distended Vein)

Fig 2: No Flow


In the absence of DVT, the entire deep venous system between the common femoral vein and the trifurcation of the popliteal vein should collapse with complete apposition of the vein walls during gentle compression. The inability to completely compress the vein lumen is the principal criterion for the diagnosis of DVT. In patients with DVT, several adjunctive US findings may be observed that are less sensitive and less specific than vein compressibility as diagnostic parameters. Acute DVT usually causes distention of the involved vein, and Doppler evaluation may reveal absence of flow (Fig 1 & Fig 2). If there is incomplete obstruction of the vein lumen, there is usually loss of the phasic respiratory venous flow pattern and a continuous flow wave may be observed that is minimally affected by augmentation. Acute DVT is often anechoic and cannot be distinguished from a normal vein. With time, the clot usually will become echoic. In the absence of DVT, internal echos due to artifact of slow-flowing blood may be observed within vein lumina. Thus, lack of vein compression is required to confirm the presence of DVT. Over time, the US appearance of DVT will evolve. In some areas of the vein, the thrombus may become increasingly echogenic and the intima of the vein wall may thicken and become echogenic and resistant to compression. However, other areas of the vein may revert to normal both in appearance and in response to compression.
The major advantages of US over other noninvasive techniques in the evaluation of patients with suspected DVT are its greater accuracy and its ability to depict anatomic variations (eg, duplicated venous segments) and alternative causes of symptoms. Diagnoses that may be discovered during the US examination include intact or ruptured Baker cysts, hematomas or other localized masses, superficial phlebitis, and arterial aneurysms or pseudoaneurysms.

Venography should be performed as a confirmatory test in the postoperative setting to avoid the unnecessary risk and cost of antithrombotic therapy in patients with false-positive results. Although US is less sensitive for the diagnosis of proximal DVT in the postoperative setting, some have continued to advocate its potential role as a screening test following high-risk surgical procedures.

Spiral CT Evaluation of Deep Vein Thrombosis 

The introduction of spiral CT (CT-V) has revolutionized CT evaluation of the vascular system. The rapid data acquisition in spiral CT allows scanning of a volume of tissue in a short period of time, thus optimizing vessel contrast with iodinated contrast material. Many authors feel that though color Doppler has a good sensitivity and specificity range of over 95% for femoral and popliteal DVT, it is less accurate for detecting DVT in the calf and pelvis veins.

 

Fig 3 (No filling of calf veins)

Fig 4 (Opacification of collaterals)


Major criteria for detecting DVT by spiral CT venography is the presence of  a filling defect in an opacified vein (Fig 3), non-opacification of a venous segment if the vein distal and proximal to the non-opacification is opacified, venous dilatation, soft-tissue density infiltration of fat suggestive of edema, and opacification of collateral veins (Fig 4). The findings of non-opacification of venous segments without venous dilatation, irregular borders of the venous walls, and opacification of collateral veins are diagnostic of post-phlebitic syndrome.

Limitations of CT-V include need for IV contrast administration,  images may be difficult to interpret cephalad to bifurcations, and flow-artefacts

Advantages include better imaging of calf and pelvis veins, higher detection in silent DVT, and advantage of imaging for pulmonary embolism simultaneously.

 

References

  1. Ginsberg JS. Management of venous thromboembolism. N Engl J Med 1996; 335:1816-1828.
  1. Salzman EW, Hirsh J. The epidemiology, pathogenesis, and natural history of venous thrombosis. In: Colman RW, Hirsh J, Marder VJ, Salzman EW, eds. Hemostasis and thrombosis: basic principles and clinical practice. 3rd ed. Philadelphia, Pa: Lippincott, 1995; 1275-1297.
  1. Lensing AWA, Hirsh J, Buller HR. Diagnosis of venous thrombosis. In: Colman RW, Hirsh J, Marder VJ, Salzman EW, eds. Hemostasis and thrombosis: basic principles and clinical practice. 3rd ed. Philadelphia, Pa: Lippincott, 1995; 1297-1322.
  1. Anderson FA, Wheeler HB, Goldberg RJ, et al. A population-based perspective of the hospital incidence and case-fatality rates of deep vein thrombosis and pulmonary embolism: the Worcester DVT study. Arch Intern Med 1991; 151:993-938.
  2. Fraser JD, Anderson DR. Deep Vein Thrombosis: Recent Advances and Optimal Visualization with Ultrasound. Radiology 1999; 211 (1): 9-24.
  3. Baldt MM, Zontisch T, Kainberger F, FleischmannG, Mostbeck G. Spiral CT Evaluation of Deep Vein Thrombosis. Sem in USG-CT-MRI Oct 1997 18 (5); 369-376.

 

CONTRIBUTION
DR. RAHUL SACHDEV
BR DIAGNOSTICS
NEW DELHI