AJR 2001; 177:319-323
© American Roentgen Ray Society
Deep Venous Thrombosis
Spectrum of Findings and Pitfalls in Interpretation on CT Venography
Kavita Garg1 and
Jie Mao
1
Both authors: Department of Radiology, Veterans Affairs Medical Center and
University of Colorado, 1055 Clermont St., Denver, CO 80220.
Received December 15, 2000;
accepted after revision January 31, 2001.
Address correspondence to K. Garg.
Introduction
Venous thromboembolism is a major national health problem, with an overall
age- and sex-adjusted incidence of more than 1 per 1000 annually
[1]. Most pulmonary emboli
originate from the femoropopliteal veins. Recently, a comprehensive test that
uses CT pulmonary angiography and venography to evaluate both deep venous
thrombosis and pulmonary embolism has been proposed in place of two or more
separate examinations
[2,3,4].
This article illustrates the findings of acute and chronic deep venous
thrombosis on CT venography that has been performed in addition to CT
pulmonary angiography. The findings are correlated with sonography in select
cases. Pitfalls in interpretation of CT venograms are briefly discussed.
Technique
CT Venography
CT venography is typically performed after CT pulmonary angiography without
using additional contrast material. CT pulmonary angiograms are first obtained
using 100-150 mL of IV contrast agent administered at a rate of 4 mL/sec with
a delay of 15-20 sec before scanning. Three to four minutes after the start of
injection, 5-mm-thick axial CT venograms are acquired from the knees to the
mid abdomen. The venographic technique may vary in different institutions. In
a recent study [5],
investigators examined the lower extremity deep venous system using contiguous
10-mm-thick axial sections from the iliac crest to the popliteal fossa.
Leg Sonography
Leg sonography is generally performed with a 5- or 7-mHz linear array
transducer. The diagnostic criteria used for acute deep venous thrombosis are
lack of complete lumen obliteration with compression, flow void on color
Doppler scans, and lack of flow detection at spectral analysis
[6]. Venous expansion, if
present, helps confirm the finding of acute deep venous thrombosis. Criteria
used for chronic deep venous thrombosis are vessel noncompressibility, wall
thickening, and luminal contraction with or without flow at spectral analysis
and color Doppler sonography. Valsalva's maneuver is performed to assess
valvular incompetence.
CT Venographic Findings
Acute Deep Venous Thrombosis
The primary criterion used to diagnose acute deep venous thrombosis is the
presence of a definite intraluminal filling defect with or without distention
of the vein (Fig.
1A,1B,1C,1D).
In most patients, an intraluminal filling defect involves multiple venous
segments and is seen on multiple contiguous images (Fig.
1A,1B,1C,1D).
However, on occasion, the defect is seen on a single image only. To avoid
false-positive results, this defect should be confirmed or correlated with
sonographic findings before instituting anticoagulation therapy. The involved
vein may show wall enhancement. An increase in caliber indicates that the
thrombus is acute (Fig.
1A,1B,1C,1D).
In patients with atrophic musculature, acute deep venous thrombosis may be
seen in smaller than normal veins (Fig.
2). Focal wall thickening due to adherent chronic deep venous
thrombosis may cause a nonoccluding intraluminal filling defect that can mimic
acute deep venous thrombosis (Fig.
3A,3B).
The common sites of acute deep venous thrombosis shown on CT venography are
the knee and groin, similar to what has been reported and seen with
sonography. Superficial femoral vein involvement is commonly seen on CT
venography. Involvement of the pelvic veins and the inferior vena cava is less
common
[4,5].
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Fig. 1B. —Acute deep venous thrombosis in 72-year-old man suspected of
having pulmonary embolism. Axial CT venogram shows intraluminal filling defect
(arrow) in left common iliac vein at its confluence with right iliac
vein.
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Fig. 1C. —Acute deep venous thrombosis in 72-year-old man suspected of
having pulmonary embolism. Axial CT venogram shows nearly occluding filling
defect in left common femoral vein (arrowhead) with enhancement of
its walls.
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Fig. 1D. —Acute deep venous thrombosis in 72-year-old man suspected of
having pulmonary embolism. Axial CT venogram shows occluding intraluminal
filling defect in right popliteal vein. Thrombosed popliteal vein
(arrow) shows increase in caliber.
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Fig. 2. —Acute deep venous thrombosis in 48-year-old man with
amputation below knee of right leg. Axial CT venogram shows intraluminal
defects (arrows) with enhancing walls in right superficial and deep
femoral veins. Right thign musculature is atrophic.
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Fig. 3A. —Focal wall thickening mimicking acute deep venous thrombosis
in 66-year-old man suspected of having pulmonary embolism. Axial CT venogram
shows nonoccluding defect (arrow) along posterior aspect of right
common femoral vein.
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Fig. 3B. —Focal wall thickening mimicking acute deep venous thrombosis
in 66-year-old man suspected of having pulmonary embolism. Longitudinal color
Doppler sonogram (shown here in black and white) or right common femoral vein
shows thickening of posterior wall (arrowheads) consistent with
chronic deep venous thrombosis. This finding was unchanged compared with
previous sonogram obtained 6 months earlier.
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Chronic Deep Venous Thrombosis
Findings of chronic deep venous thrombosis on CT venography include
calcified thrombi, heterogeneously enhancing small thick-walled veins, and the
presence of collateral veins (Figs.
4A,4B,4C,4D,4E
and
5A,5B).
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Fig. 4A. —Chronic deep venous thrombosis in 74-year-old man undergoing
dialysis because of chronic renal failure. Axial CT venogram obtained at level
of inguinal ligament shows calcified thrombi in common femoral veins
(arrows).
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Fig. 4B. —Chronic deep venous thrombosis in 74-year-old man undergoing
dialysis because of chronic renal failure. Axial CT venogram obtained 2 cm
superior to A shows intraluminal filling defect in left common femoral
vein, which suggests acute thrombus (arrow).
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Fig. 4C. —Chronic deep venous thrombosis in 74-year-old man undergoing
dialysis because of chronic renal failure. Transverse sonogram of left common
femoral vein shows intraluminal echogenic material without shadowing
(arrow). Vein was not compressible. It is known that thrombus
echogenicity is not an accurate criterion for determining age of venous
thrombosis.
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Fig. 4D. —Chronic deep venous thrombosis in 74-year-old man undergoing
dialysis because of chronic renal failure. Longitudinal sonogram shows some
flow in left common femoral vein and monophasic waveform that does not
decrease to baseline with inspiration. Lack of changes with respiration
suggests iliac vein obstruction.
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Fig. 4E. —Chronic deep venous thrombosis in 74-year-old man undergoing
dialysis because of chronic renal failure. Axial CT venogram of right distal
superficial femoral vein shows intraluminal calcification in otherwise
normally enhancing vein (solid arrow). Three smaller venous
collaterals (open arrows) surrounding artery are also seen.
Calcification and collateral veins were not revealed on sonography, but right
superficial femoral vein wall thickening was shown only on sonography (not
shown).
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Fig. 5A. —Acute and chronic venous thrombosis in 64-year-old man with
small cell lung carcinoma. Axial CT venogram shows small heterogeneously
enhancing right superficial vein (straight arrow), acute thrombus in
greater saphenous vein (curved arrow), and large profunda vein
(arrowhead).
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Fig. 5B. —Acute and chronic venous thrombosis in 64-year-old man with
small cell lung carcinoma. Longitudinal sonogram using color Doppler of
proximal right thigh shows recanalized small superficial femoral vein
(arrowheads) and capacious profunda vein shown in black and white
(arrow) with normal flow. Valvular incompetence indicated by reversed
flow on spectral waveform during Valsalva's maneuver was also noted (not
shown).
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Residual changes from acute deep venous thrombosis may be seen in up to 50%
of sonograms at 6 months and may persist indefinitely. Venous insufficiency is
a common sequela of deep venous thrombosis. This condition results in reverse
flow in the veins, which is revealed on sonography by using Valsalva's
maneuver. Recanalization of a small vein is also better shown on sonography
than on CT venography. The lack of venous compression is a much less specific
diagnostic sign for recurrent deep venous thrombosis. Neither sonography nor
CT venography may be able to accurately differentiate acute from chronic deep
venous thrombosis in a patient. Therefore, both CT venography and sonography
should be used in unresolved cases to evaluate the chronicity of venous
thrombus. An accurate differentiation of acute from chronic deep venous
thrombosis is important to determine the need and duration of anticoagulation
therapy. It is also important when the safety and efficacy of new thrombolytic
or anticoagulant therapy is being investigated
[7].
Acute and Chronic (Recurrent) Deep Venous Thrombosis
A diagnosis of recurrent deep venous thrombosis can be made when findings
of acute and chronic deep venous thrombosis coexist on CT venography (Fig.
5A,5B).
Pitfalls in Interpretation
The most common pitfall in interpretation of CT venograms is an apparent
intraluminal filling defect caused by flow-related inhomogeneous opacification
of the vein (Fig. 6).
Suboptimal opacification can also result in a false-negative study
[4]. Beam-hardening artifacts
caused by adjacent calcifications (Fig.
7) and prosthetic joints or orthopedic hardware can result in
pseudo filling defects. Anatomic variations such as duplicated veins or a
dominant profunda femoris vein may potentially be misinterpreted as collateral
veins (Fig. 8). An arterial
thrombus can be easily differentiated from a venous thrombus if these vessels
are systematically followed from slice to slice.
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Fig. 6. —Flow artifact on CT venogram in 64-year-old man suspected of
having pulmonary embolism. Axial CT venogram shows apparent filling defect
(arrow) in left common femoral vein. Complete compressibility of this
vein was seen on sonography (not shown). Flow artifacts are caused by
inadequate delay before scanning. These artifacts are commonly seen on CT
venograms in patients with significant peripheral artery disease, even with
longer delay.
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Fig. 7. —Beam hardening artifact on CT venogram in 75-year-old man
suspected of having pulmonary embolism. Axial CT venogram of right superficial
vein shows apparent sharply demarcated filling defect (arrow) caused
by superficial femoral artery calcification.
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Fig. 8. —Anatomic variation of deep venous system in 50-year-old man
suspected of having pulmonary embolism. Axial CT venogram shows duplicated
right superficial vein (open arrows) and dominant profunda femoral
vein on left (solid arrow). Duplicated superficial femoral vein is
common anatomic variation. Duplicated venous segments may be seen on one image
or on multiple contiguous images.
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Conclusion
A spectrum of findings on CT venography can be seen in patients with deep
venous thrombosis related to chronicity of thrombi. In most cases acute deep
venous thrombosis can be differentiated from chronic deep venous thrombosis.
However, the findings of acute and chronic deep venous thrombosis may overlap
or may truly coexist. CT venography and sonography play complementary roles,
and both should be used in unresolved cases. The most common difficulty in
interpretation arises when inhomogeneous opacification creates a pseudo
filling defect that mimics venous thrombosis. Unless the veins show good
homogeneous opacification, CT venograms should be interpreted with caution to
avoid false-positive or false-negative results.
Acknowledgments
This article is dedicated to the memory of Marsha Heinig, M.D., Ph.D.
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