Non-traumatic thoracic emergencies: CT venography inanintegrated diagnosticstrategy ofacute pulmonary embolism andvenous thrombosis

Published online: 21 June 2002 © Springer-Verlag 2002 Categorical Course ECR 2003

Abstract Deep venous thrombosis and pulmonary embolism are the two aspects of venous thrombo-embo-lism. Investigation of lower limb veins has been part of various diag-nostic algorithms in the past 15 years. Recently, the combination of CT ve-nography (CTV) of lower limbs and abdominal veins together with CT angiography of the pulmonary arte-ries has allowed a complete exami-nation of venous thrombo-embolism in one session. The technical aspects, imaging findings, venous anatomy

on CT, interpretative pitfalls, results and advantages of CT venography are reviewed.

Keywords Veins · Thrombosis · Pulmonary arteries · Venography · CT

Benoit Ghaye

Robert F. Dondelinger

Non-traumatic thoracic emergencies:

CT venography in an integrated diagnostic

strategy of acute pulmonary embolism

and venous thrombosis

Introduction

Deep venous thrombosis (DVT) and pulmonary embo-lism (PE) are two aspects of the same disease process, termed venous thrombo-embolism (VTE), and consti-tutes major health problems that result in significant morbidity and mortality [1, 2, 3, 4]. It is estimated that VTE is associated with 300,000–900,000 hospitaliza-tions per year in the US and results in 50,000 to 150,0000 deaths [1, 5, 6]. Early diagnosis and treatment significantly improve survival in patients with VTE [7]. Clinical diagnosis and treatment of DVT and/or PE is difficult. The use of non-invasive and invasive testings vary, as the clinical manifestations of VTE are diverse [6]. Although ventilation–perfusion (V/Q) lung scanning has been a common screening test in the evaluation of suspected PE, spiral CT angiography (SCTA) is used in-creasingly, because it accurately defines emboli down to level of the segmental pulmonary arteries, while reveal-ing other non-embolic causes of thoracic symptoms [8, 9, 10]. Criticism has been raised against SCTA as a screening test for VTE. Firstly, small clots located distally to the segmental level may be missed even on a

high-quality examination, exposing untreated patients to the risk of recurrent PE. Secondly, patients may be unable to hold their breath for 10–40 s, and SCTA may be difficult to interpret in case of breathing artifacts (i.e. intensive care unit patients). Thirdly, SCTA has been considered indeterminate in 2–13% of the patients [10]. Some of the limitations will probably be overcome with the use of multi-slice CT (MSCT), but the role of SCTA relative to V/Q scanning currently remains a debate among clini-cians. A small pulmonary embolus may herald larger emboli, which imposes intensive evaluation of venous clots [11,12]. While clots in the lungs clearly influence the cardio-pulmonary status of the patients, the major risk of death is from recurrent PE. In the PIOPED study, a recurrent embolic event was the cause of death in 90% of the patients dying of PE [13]. Deep venous thrombo-sis is often asymptomatic, and approximately 90% of PE arise from deep veins of the legs and pelvis [1]; there-fore, it appears that optimization of resolution of SCTA is of less clinical importance than accurate assessment of residual DVT. Furthermore, dual assessment of both as-pects of the disease is important with respect to thera-peutic implications [6]. A common strategy emerged that B. Ghaye (

✉

Department of Medical Imaging, University Hospital Sart Tilman,

Domaine Universitaire du Sart Tilman B35, 4000 Liege, Belgium

e-mail: bghaye@chu.ulg.ac.be Tel.: +32-4-3667259

included SCTA, followed by US, to rule out DVT in the extremities [11, 14]. Although at our institution US of the lower limbs is the primary imaging modality for the diagnosis of DVT, a single examination that accurately depicts both PE and the presence of DVT would be de-sirable to avoid delay in the diagnosis of VTE and limit cost.

History

Before the 1970s, the diagnosis of DVT was almost ex-clusively based on conventional venography (VG). In-jection of contrast medium in the veins of the lower ex-tremities was among the first descriptions of diagnostic angiography [15]. Because of the relative invasive nature of VG, many non-invasive techniques have been devel-oped, including blood tests (i.e. d-dimers), radionuclide venography, impedance plethysmography (IPG), US, CT and MR. Introduced in the mid-1980s, US of leg veins is currently the most commonly used and usually only test in patients suspected of DVT [16]. In 1978, Steele et al. first reported incidental detection of inferior vena cava (IVC) thrombosis with CT in two patients [17]. In 1980, Zerhouni et al. reported five cases demonstrating CT findings of ilio-femoral venous thrombosis [18]; thereaf-ter, CT findings of DVT were refined in many papers published during the early 1980s [19, 20, 21, 22, 23, 24]. In 1987, Pillari et al. reported a series of 14 patients sus-pected of DVT who underwent CT of the legs after a negative venography. Computed tomography was per-formed from the patella to the inferior third of the calves during infusion of 30% contrast medium in a foot vein. No further DVT was demonstrated, but abnormalities, such as muscular haemorrhage or occult knee-joint effu-sion, responsible for the clinical symptoms, were shown [25]. In 1988, Bauer and Flynn reported the clinical use of indirect CT venography (CTV) in patients with incon-clusive conventional venography, or when venous access in the foot was impossible. The CT scanning of the lower extremities and pelvis was obtained during a slow infusion of 150 ml of contrast medium in an arm vein for 10 min [26]. In 1991, Langer et al. reported a series of indirect CTV from the ankles to the pelvis in 15 patients. In the 6 patients suspected of PE, the thorax was also scanned and concomitant pleuro-parenchymal changes were demonstrated. This report was the first to promote a combined incremental CT examination of the thorax, lower limbs, and pelvis in patients suspected of VTE [27]. In 1994, Stehling et al. reported the first case of di-rect spiral CTV of the lower limbs following injection through a catheter inserted in a dorsal vein of the foot [28]; however, it was not until 1998 that Loud et al. re-ported the combination of SCTA of the pulmonary arte-ries and indirect CTV in 5 patients suspected of VTE. Veins were imaged from the lower calves to the

dia-phragm thanks to contrast medium recirculation that fol-lows rapid infusion for SCTA [3].

Diagnostic imaging of DVT

Ascending venography (VG) is still currently accepted as the most reliable test for the diagnosis of DVT and the gold standard against which all diagnostic tests should be evaluated [15, 26]. Ascending venography is consid-ered the only technique available that accurately depicts all calf and muscular venous thrombi. A variation of the basic technique may be necessary if initial results are doubtful. Using proper technique in a cooperative pa-tient, it is almost always possible to define the deep ve-nous system and to determine whether occlusion is acute or chronic. This invasive test is limited only by technical factors and complications which may be minimized by using a careful technique [15]. Inter- and intra-observer variability confirmed important operator dependence and the need for experience to perform and interpret the ex-amination [29, 30].

Ultrasound is an established and widely available technique for evaluation of the veins of both the lower and upper extremities. Advantages include non-invasive and inexpensive technique, and the ability to perform the examination at the patient’s bedside. In a large meta-anal-ysis, US showed sensitivities of 92–100% and specifici-ties of 80–100%, when compared with VG for proximal veins in symptomatic patients. For distal or calf veins, sensitivity was 40–87% depending on the technique used. In asymptomatic patients, sensitivity was 38–100% for the proximal level, and 38–58% for the calf level, con-firming that none of the US examination techniques had a sufficiently high sensitivity for calf veins [16].

Similar to CT, MR has the ability to allow for a com-bined evaluation of pulmonary embolism and venous thrombosis. Preliminary results of MR venography showed results similar to ascending VG [31, 32]. Wide-spread availability, lower cost, shorter examination time and higher accuracy for peripheral pulmonary arteries are currently the main advantages of CT over the emerg-ing MR imagemerg-ing.

In nuclear medicine imaging, radiolabelled thrombus-detecting agents are investigated, with the potential of screening the whole body for thrombo-embolic disease in a single examination, and differentiating between acute or chronic thrombosis [33].

Direct CT venography

medium into the deep venous system. Axial, multiplanar and maximum intensity projection images allowed dif-ferentiation of acute DVT from chronic thrombus in a patient with ambiguous sonographic and venographic findings. Potential advantages over venography were the ability to perform 3D imaging, a tenfold reduction of contrast medium volume, increased patient comfort due to the low concentration of contrast medium, a supine position and a decreased risk of post-injection phlebitis. Layering of contrast medium in the vein may remain nevertheless a factor of suboptimal opacification [28]. One study compared direct spiral CTV with convention-al venography in 52 patients. Sensitivity of direct spirconvention-al CTV was 100%, specificity 96%, positive predictive val-ue 91% and negative predictive valval-ue 100%. The exten-sion of DVT, particularly in pelvic veins and IVC was better demonstrated with CTV. Interobserver agreement was 0.81–0.93 and 0.71–0.88 for direct CTV and con-ventional venography, respectively. Intra-observer agree-ment was 0.91–0.94 and 0.75–0.92, respectively. Global venous opacification was significantly better with direct CTV, despite a 80% reduction of the volume of contrast medium (40 vs 200 ml). Major differences were found in the IVC, pelvic veins and deep femoral veins. Only 11% (compared with 25% with venography) of all deep veins were not opacified. The technique is less operator depen-dent than US or venography but remains susceptible to inflow phenomena that can mimic intraluminal filling defect. The deep venous system is not always opacified entirely, and puncture of both feet veins is required [34, 35]. The same group also applied the technique to evalu-ation of venous thrombosis in the upper extremities [35, 36]. Direct CTV better demonstrates the relation be-tween thrombi and vessel wall, confirming that conven-tional venography overestimated the prevalence of free-floating clots [37].

Indirect CT venography

Combined SCTA of the pulmonary arteries and indirect CTV of the lower limbs allow for a complete one-ses-sion evaluation of VTE [3, 38, 39, 40, 41, 42].

Image interpretation

In clinical practice, the differentiation between acute and chronic DVT is important for determination of the need for anticoagulation and duration of treatment [15, 43, 44].

The CT signs of acute DVT

Basic CT signs of acute DVT have been described in case reports published in the 1980s [17, 18, 19, 20, 21,

22, 23, 24, 45, 46, 47]. The primary CT sign used to di-agnose DVT is the demonstration of intra-vascular clot, presenting as a complete, partial or mural filling defect, depending on the degree of venous occlusion (Figs. 1, 2). Recognition of clot with CT may be difficult in some cases, as fresh thrombus may exhibit attenuation values similar to contrast-enhanced blood [18, 39]. Additional findings may contribute to establish the diagnosis. A non-opacified venous segment that is sandwiched by an opacified distal and proximal segment has to be inter-preted with caution. Other signs of acute DVT include venous dilation compared with the normal contralateral side, obliteration of perivenous fat suggestive of edema, Fig. 1 Proximal acute deep venous thrombosis (DVT) in a 69-year-old woman. Axial CT venogram at the level of the thigh shows typical findings of DVT in the right groin. An endoluminal filling defect is demonstrated in the right common femoral vein (arrow), which is enlarged compared with the left normal side. Note also extensive peri-focal oedema infiltrating the fat. A clot is also demonstrated in the right greater saphenous vein (arrowhead)

erogeneous lumen and strands. Multiple deep or superfi-cial collaterals are commonly encountered. Other signs include small retracted veins and ultimately a fibrous cord replacing the vein [49]. Some chronic clots may show vein dilation, or perivascular and soft tissue ede-ma, which makes differentiation between acute and chronic disease sometimes difficult [44, 50, 51].

The CT signs of recurrent DVT

Association of findings of acute and chronic DVT on CTV suggests the diagnosis of recurrent DVT (Fig. 3b) [44]. Recurrent DVT is a major challenge in diagnostic imaging [52, 53]. Comparison with previous examinations improves confidence in diagnosis. Both CTV and US have been suggested to have a complementary role in unsolved cases [44]. The accuracy of CTV in predicting the age of the thrombus and recurrent DVT needs to be assessed.

Examination protocol

How to perform data acquisition

Patients are positioned supine on the CT table with the feet directed towards the gantry. Feet are placed in the head holder or on a table extender and immobilized to-gether with tape to limit leg motion. This patient orienta-tion allows for scanning from the ankle to the cervico-thoracic junction without repositioning the patient. Legs are maintained slightly elevated on a folded blanket to avoid compression of the calf veins. Some centres use tourniquets for preferential opacification of the deep ve-nous system [54]. Elastic stockings have recently been reported to increase venous enhancement at popliteal, femoral and iliac levels between 28 and 32% (p<0.0005) [55]. The arms are placed over the patient’s head as with SCTA. Firstly, a scout view of the thorax is obtained. Next, 120–150 ml of 240–300 mg iodine/ml contrast me-dium are injected at a flow rate of 3–5 ml/s through an antecubital vein for acquisition of SCTA. After comple-tion of examinacomple-tion of pulmonary arteries, the table is manually moved and the reference laser placed at the level of the ankles. The CTV starts approximately 210 s following the start of injection using either sequential or spiral scanning. With sequential technique, 5- to 10-mm-thick slices are acquired every 20–50 mm. Total elimina-tion of the secelimina-tion interval would lead to only a minimal increase in sensitivity for DVT, while resulting in a sub-stantial increase in radiation dose, number of images and cost [51]. Of the patients, 2.1% had DVT visible on one slice only when using a 20-mm slice interval. A slice in-terval >2 cm can potentially lead to either false-negative findings on CTV or an underestimation of the extent of DVT [43]. Using spiral technique, 3.75- to 10-mm-thick high contrast ring-like rim of the venous wall due to

con-trast staining in the vasa vasorum or concon-trast accumula-tion around intraluminal clot, muscular swelling and opacification of collateral veins [3, 39]. Prolonged arteri-al phase of enhancement may occasionarteri-ally be seen in pa-tients with extensive bilateral DVT [48].

The CT signs of chronic DVT

slices are usually obtained [41, 48, 54, 56, 57, 58]. With multi-slice CT, a length of 100 cm can be scanned in ap-proximatively 20 s, using 4×5-mm collimation, 0.5-s ro-tation time and a pitch of 1.8 [59].

Which level of irradiation dose

Additional technical parameters influencing the dose de-livered to the patient have to be carefully selected. To the best of our knowledge, there is no published study com-paring different irradiation parameters for CTV. In pub-lished clinical studies using spiral CT, parameters were variable (75–260 mA and 120–150 kVp and a pitch of 1–1.5) [41, 54, 56, 57]. “Low-dose” technical parameters (75 mAs, 120 kVp) have been shown to be adequate when using dual-detector spiral CT, 6.5-mm slice thickness, 20-mm/s table feed and 1-s rotation [54]. With sequential CT, we use 100 mA and 130 kVp [60]. One study estimat-ed the dose of CTV to be slightly less than that of a stan-dard pelvic CT [41]. Another study calculated the effec-tive radiation dose of combined spiral SCTA–CTV to be approximately 57% of a dual-phase spiral CT of the liver (4.75 vs 8.3 mSv). Although such an evaluation depends on the specific technical parameters and type of scanner used, it demonstrated that spiral CTV was responsible for 50% of the effective dose of the combined SCTA–CTV technique and for a significant increase in the gonadal dose. Although the risk–benefit ratio remains limited in a mainly aged population, indications of CTV should be considered carefully in younger patients [61].

When to perform data acquisition

Screening during the optimal time window for CTV is important for proper clot detection. Optimal vein analy-sis requires high level of luminal attenuation, homogene-ous opacification and a sufficient vein-to-surrounding muscle gradient and vein-to-clot gradient. A gradient of 30 HU is generally considered to be sufficient.

Morphology and density of clots measured in vivo ap-pear to vary with thrombus composition and age. Venous thrombus, generated in slow-flow conditions, are “red thrombus” composed predominantly of red blood cells. The relative concentration of protein, particularly globin, is responsible for high CT density values. Acute red thrombi have a higher haematocrit value than blood, due to increased concentration of globin [62]. Recent clots (<8 days) appear homogeneous with average densities of 31±10 HU [38], 51 HU [41], 66±7 HU [34], 76 HU [62] and 60–80 HU [50]. With time, globin is broken down and removed by phagocytes, resulting in decreased atten-uation values, which are sometimes at a lower level than normal blood [62]. Subacute or chronic clots (>8 days) tend to become heterogeneous with areas of high

attenu-ation and average densities of 28 HU [62], less than 50 HU [50] or 55±11 HU [34].

Time–density curves of venous enhancement follow-ing SCTA have been studied usfollow-ing sequential, or spiral or multi-slice CT [42, 60, 63]. The time–density curves for the veins of lower limbs are presented in Fig. 4. Curves at different levels of the lower limbs showed that all density values comprised in the time interval from mean peak venous enhancement (ranging from 93 to 137 HU) to mean densities at 420 s (ranging from 88 to 103 HU) were above reported attenuation of recent clots. Time to reach maximum enhancement increased from IVC (93±9.5 s) to popliteal veins (141±57 s) and de-creased for calf veins (124±32 s) [60].

Homogeneity of venous enhancement is another pa-rameter that affects clot detection during CTV. Homoge-neous enhancement is obtained after 150 s for above-knee veins, except for femoral vein (180 s), and 210 s for veins below the knee (Fig. 5) [60].

When considering time–density curves, homogeneous venous opacification, vein-to-muscles and vein-to-clot gradients at different levels, an optimal time window for CTV was determined to be between 210 and 240 s for the calf level and 180–300 s for above-knee veins. When using a sequential acquisition for CTV, a caudo-cranial acquisition is recommended, which starts at 210 s for the sural level (optimal time window). For faster CTV tech-nique, such as multi-slice CT, the choice of direction of acquisition is irrelevant [60].

Similar levels of enhancement (91–101 HU) were re-ported in clinical practice for above-knee veins, when starting CTV 180–210 s after contrast medium injection [38, 41, 64].

heart failure, severe distal arterial obstruction or impaired flow dynamics, such as abdominal vein compression, adding a further delay of 60 s is recommended before CTV acquisition [40]. A contrast–blood interface is occa-sionally observed in dilated varicosities, due to local low flow [49, 65]. Rescanning the area 1–2 min later shows homogeneous filling in varicosities with normal lumen; however, insufficient venous opacification can occur in an unpredictive manner, which may limit CTV in some patients [63]. Figure 6 shows quality of venous enhance-ment obtained in our experience. In clinical practice, suf-ficient and homogeneous enhancement is obtained in 84–99% of the patients depending on the anatomic level (Fig. 6). Poor opacification leading to indeterminate re-sults for CTV has been reported in 1–5% of the patients [38, 40, 41, 43, 48, 64]. In one study, patients with fair- to poor-quality SCTA (5%; 27 of 541) were more likely to have fair- to poor-quality CTV (52%; 14 of 27) [41].

Venous anatomy

Computed tomographic venography enables recognition of DVT in veins which are difficult to assess with US or ascending venography, such as deep femoral vein, internal iliac vein, gonadal vein, renal vein and hepatic vein. Com-bination with SCTA may further demonstrate clots in the right heart, superior vena cava, right and left innominate veins and the distal part of subclavian and jugular veins. Normal anatomy

Figure 7 shows the normal anatomy on an ascending ve-nography with correlated CTV sections at different levels. Diameter of the veins reflects their capacious role. The ve-Fig. 5a, b Heterogeneous venous enhancement. a Axial CT

veno-gram at the groin level shows a pseudo-filling defect in both com-mon femoral veins (arrows). Scanning was performed less than 180 s after start of contrast medium injection. b Axial CT veno-gram evidences normal enhancement after rescanning 30 s later (arrows)

nous calibre is similar to that of the corresponding artery for popliteal vein, superficial and common femoral veins, external and common iliac veins and IVC. Veins below the popliteal level, deep femoral vein and internal iliac vein have a calibre superior to the corresponding artery. Greater and lesser saphenous veins, as other superficial veins, are not accompanied by a corresponding artery. Anatomic variants

Anatomic variants should be recognized to avoid false-negative results of CTV. Duplication is usual for

posteri-or tibial, anteriposteri-or tibial and peroneal veins. Partial dupli-cation of popliteal and/or superficial femoral veins may be frequently encountered, particularly in patients with DVT. The IVC may be occasionally duplicated or left sided (Fig. 8) [66, 67]. Duplication represents a classic pitfall in US [49, 51]. Embryologic remnants of the sci-atic vein may rarely be seen with popliteal vein draining either in deep femoral vein (partial form), or in internal iliac vein (complete form; Fig. 7). Unusual venous path-ways may be associated with absence of usual normal venous segment.

Interpretive pitfalls

Pitfalls related to the technique

Computed tomographic venography may be performed using sequential or spiral technique. Theoretical advanta-ges of the sequential technique is to reduce the number of slices and total irradiation. We perform 5-mm slice every 20 mm (15-mm interslice gap) [39], whereas others use 5- to 10-mm-thick sections every 50 mm (40-to 45-mm interslice gap) [3, 38, 51, 68] or 10 mm every 20 mm (10-mm interslice gap) [40]. We found that a Fig. 7 Venous anatomy of the lower limbs. Normal venous

anato-my is shown on venography and corresponding slices obtained by CT venography (CTV). The veins that could be correctly analysed on axial CT venograms are annotated on the slices. Veins repre-sented in blue are visible on CTV and are usually poorly or non-opacified on state-of-the-art venography (RV, GonV, IIV, CxV, GSV, DFV and LSV). Most of these veins are also among the most difficult to study on US examinations. Veins represented in green are anatomic variants and include duplicated inferior vena cava (IVC) or left-sided IVC (LIVC), direct continuation of the PV in the IIV (PV-IIV cont), direct continuation of the PV in the DFV (PV-DFV cont) and duplication of PV (PV dupl) or SFV (SFV dupl)

▲

maximum 5-mm collimation is necessary to avoid par-tial-volume averaging on small veins, particularly veins presenting a transaxial or oblique course, and that a 15-mm interslice gap is acceptable. Small non-occlusive DVT involving a short venous segment, especially in asymptomatic patients, has been detected, although its clinical significance is not clear (Fig. 9) [40]. Two short areas of clots in superficial and common femoral veins were missed, when using 40- to 45-mm interslice gap in 308 patients (0.6%) [51]. We perform a “live” inter-pretation of CTV on the screen during and after acquisi-tion. For doubtful images, a short spiral sequence of 5-mm collimation is acquired over the problematic area (Fig. 10). Another option is to correlate findings with so-nography [44]. Multi-slice CT using 5-mm collimation or less may become routine in the future, but cost-effec-tiveness and irradiation have to be evaluated [40].

Inhomogeneous opacification of the veins may cause pseudo-filling defects, which may simulate DVT [44, 49]. Such artefacts may be flow-related or due to im-proper selection of scanning time [40, 49, 69, 70, 71]. Rescanning 60 s later eliminates these artefacts (Fig. 5).

Computed tomographic venography acquired with “low dose” or too thin slices can produce noisy images with lumen of the vessels difficult to interpret, particu-larly in obese patients [72].

Normal or pathological structures

Some normal structures may present with a hypervascu-lar rim and a central hypodensity mimicking DVT: vol-ume averaging integrating a venous valve, lymph node, sciatic nerve, aponeurosis or tendon, obstructed and di-lated ureter or bowel loop with non-opacified lumen (Fig. 11) [18, 23, 48, 49, 73]. Abnormal or pathological structures may also wrongly suggest DVT, including thrombosed arteries or by-pass, haematoma, abscess, popliteal cyst and acute compartment syndrome [49].

Streak artefacts

Orthopaedic material, bone, calcification and opacified bladder or ureter can produce streak or beam-hardening artefacts, which may be responsible for endovascular hy-podensities when crossing a normally opacified vessel (Fig. 12). The sharp and straight appearance of these artefacts that extend in the surrounding tissues may help to the correct diagnosis [41, 49].

Potential benefits of combined SCTA and CTV

aspects of VTE, which allows for immediate treatment of patients who have isolated DVT, without further delay of other types of diagnostic examinations. No separate venipuncture or additional contrast medium injection are necessary, as only the contrast medium already in circu-lation from SCTA is used. Little time (30–240 s) is added to the overall examination duration, depending on the technique used, with negligible additional cost. Total room transit time of the patient is between 15 and 25 min. Preliminary results have suggested that com-bined SCTA–CTV is more cost-effective in selected pa-tients than a combination of other tests [74]. The techni-cal quality of CTV is not dependent on patient

collabora-tion or mobility; therefore, it may be useful in ICU pa-tients who are intubated, or who are unable to hold their breath, or in whom leg symptoms cannot be assessed [40]. The CTV is not limited by leg cast or painful com-pression, dressing, oedema, open wounds, severe burns or trophic changes of lower limbs or obesity [40, 54, 75]. Patient comfort is increased, as no further mobilization is required. The CTV provides adequate visualization of veins that are difficult to image with other techniques, such as iliac veins and IVC, which is advantageous to guide further interventions, such as catheter placement for thrombolysis or IVC filter introduction [3]. Comput-ed tomographic venography also demonstrates unsus-pected DVT in the opposite limb [26], adjacent disease or other anomalies compressing the venous system [26, 39]. These findings may be responsible for the symp-toms and may have an impact on patient management. Examples are given by gastrointestinal tract perforation, abdominal tumour, haematoma or other fluid collections, Fig. 10a–i Comparison of

se-quential scanning and spiral scanning at the calf level in a 61-year-old woman. a–c Five-millimetre-thick axial CT venograms were acquired se-quentially 20 mm apart. Suspi-cion of DVT in a right sural vein (arrow). d–i Five-milli-metre-thick axial CT veno-grams were acquired using spi-ral technique on the same area without reinjection of contrast medium. The DVT was con-firmed in a right sural vein (arrows) as well as in other lo-cations (arrowheads)

Fig. 12 Beam-hardening artefact from opacified ureter in a 55-year-old man. Axial CT venogram at the level of the pelvis demonstrates a linear filling defect in the right internal iliac vein (arrow) that corresponds to streak or beam-hardening artefact from contrast in the right ureter located anteriorly

Fig. 13a, b Recurrent pulmonary embolism in an 83-year-old woman with a history of venous thrombo-embolism treated with percutaneous insertion of an inferior vena cava filter (ICVF). a Axial CT venogram at the level of the infrarenal IVC demon-strates tilting of the IVCF by showing the asymmetrical aspect of the struts (arrow). Recurrent DVT was evidenced in the right low-er limb (not shown). b Spiral CT angiography shows recurrent pulmonary embolism in the right lower lobe (arrows)

Fig. 14a, b Incidental demonstration of a pelvic tumor compress-ing the right iliac vein in an 81-year-old woman with acute deep venous thrombosis and non-symptomatic sub-acute pulmonary embolism. a Axial CT venogram at the level of the pelvis shows DVT in the right external iliac vein (arrow). A haematic collection is demonstrated in the uterine cavity (star). b Axial CT venogram acquired 20 mm cranial to a demonstrates large necrotic lymph nodes, metastatic of a neoplasia of the endometrium, compressing the right iliac vein (arrow)

ascitis, portal vein thrombosis and arterial embolism (Figs. 13, 14, 15) [39, 54, 56, 68]. Computed tomographic venography may also decrease multiple referrals to CT units for suspected malignancy as an underlying cause for VTE [59]. Combined SCTA–CTV results in a com-plete evaluation of potential sources of clots by screen-ing the lower limbs veins, IVC, superior vena cava and the heart chambers (Figs. 16, 17). It is a valuable base-line for follow-up of VTE or against which any further development can be evaluated [3]. The technique is less operator dependent than US or venography. A potential role in the work-up of paradoxical embolism has been suggested [76].

Clinical results

Fourteen clinical studies of combined CTV–SCTA have been published until 2002: 12 papers and 2 abstracts. The CTV has been performed using sequential [38, 39, 40, 43,

51, 68], spiral [41, 48, 56, 57, 77, 78] or mixed technique [54, 58]. Results are most often compared to US which is known to be a weak standard of reference (Table 1). Compared with US, the results of CTV were 89–100% sensitivity, 94–100% specificity, 67–100% positive pre-dictive value and 97–100% negative prepre-dictive value. Global inter-technique agreement was 0.84 to 1.00 be-tween CTV and US [39, 56, 79]. Agreement was lower for infra-popliteal veins (kappa=0.57) than for popliteal and supra-poplitel veins (kappa=0.78–0.87) [56]. Inter-observer agreement was 0.59–0.95 [43, 54, 78, 79]. The moderate correlation (kappa=0.53) between CTV or US and venography in one study can be partially explained by the fact that venography was mainly applied in pa-tients with discordant results of CTV and US [39]. Pre-liminary results did not show any difference whether se-quential or spiral technique was used. The overall detec-tion rate of DVT in CTV in patients with PE was 32–89% (mean 59%). Except for one series, CTV increased the percentage of positive results for VTE by 11–36% (mean Fig. 16a, b Pulmonary embolism originating from thrombosis of

the superior vena cava in a 48-year-old woman. a Late phase of spiral CT angiography (SCTA) shows clot in the superior vena cava (arrow). The CT venography was negative for DVT. b A CT angiogram shows segmental pulmonary embolisms in both lower lobes (arrows)

T

able

1

Published clinical studies of combined spiral CT angiography of pulmonary arteries and CT venography of lower limbs and abdomen

. US ultrasound; VG venogra-phy; IVC

inferior vena cava;

NA

non available;

PPV

positive predictive value;

NPV

negative predictive value

Reference No. of T echnique Slice Increment Region Standard Sensitivity Specificity PPV NPV Inter -patients thickness (mm) studied of (%) (%) (%) (%) technique (mm) reference agreement (n) [56] 100 Double-5.5 NA Mid-calf to US (100) NA NA NA NA k=1.00 detector retro-hepatic spiral IVC [41] 541 Spiral 10 10 Iliac crest to US (1 16) NA NA NA NA 93% popliteal fossa [48] 74 Spiral 10 NA Iliac crest to US (74) 89 94 67 98 NA knee [40] 70 Sequential 10 20 Knee to US (70) 100 97 71 100 NA renal vein [39] 209 Sequential 5 2 0 Ankle to US (199) NA NA NA NA k=0.84 diaphragm VG (51) k=0.53 [68] 150 Sequential 10 50 Diaphragm US (150) 97 100 NA NA NA to ankle [38] 71 Sequential 5–10 50 Upper calf to US (71) 100 100 100 100 NA diaphragm [54] 65 Double-6.5 5 Mid-calf to US (65) 93 97 93 97 NA detector pelvis

spiral (lower limbs) Sequential

10 40 Pelvis to VG (2) (abdomen) retro-hepatic IVC [51] 650 Sequential 5–10 50 Diaphragm US (308) 97 100 100 99 NA

to upper calf or reverse direction

23%) [40, 41, 51, 54, 58, 68, 80]. In one study the addi-tion of CTV to SCTA increased the accuracy of detecaddi-tion of VTE from 69 to 88% [74]. Other advantages were more accurate demonstration of extension of DVT, partic-ularly in pelvic and abdominal veins [39, 40, 51, 58, 79]. Additional findings and alternative diagnoses for the clin-ical symptoms were also provided by CTV [39, 54, 56, 68]. Other authors have suggested to perform limited CTV of the pelvis only or pelvis and abdomen, in combi-nation with SCTA, when a previous US was negative. In

this condition, additional DVT was demonstrated in 2–8% of the patients suspected of PE [81, 82].

In conclusion, the combination of SCTA of pulmona-ry arteries and CTV of lower limb and abdominal veins allows a complete one-session evaluation in patients sus-pected of having VTE. Further studies are required to optimize technique and evaluate cost-effectiveness. Acknowledgements Thanks to C. Coimbra for help in translation of reference published in the Portuguese language.

References

1. Moser KM (1990) Venous thromboem-bolism. Am Rev Respir Dis 141:235– 249

2. Goldhaber SZ (1998) Pulmonary em-bolism. N Engl J Med 339:93–104 3. Loud PA, Grossman ZD, Klippen-stein DL, Ray CE (1998) Combined CT venography and pulmonary angio-graphy: a new diagnostic technique for suspected thromboembolic disease. Am J Roentgenol 170:951–954 4. Shah AA, Buckshee N, Yankelevitz

DF, Henschke CI (1999) Assessment of deep venous thrombosis using routine pelvic CT. Am J Roentgenol 173:659– 663

5. National Institutes of Health (1986) Prevention of venous thrombosis and pulmonary embolism. J Am Med Assoc 256:744–749

6. Ferris EJ (1992) George W Holmes Lecture. Deep venous thrombosis and pulmonary embolism: correlative eval-uation and therapeutic implications. Am J Roentgenol 159:1149–1155 7. Dalen JE, Alpert JS (1975) Natural

his-tory of pulmonary embolism. Progr Cardiovasc Dis 17:259–270

8. Remy-Jardin M, Remy J, Deschildre F et al. (1996) Diagnosis of pulmonary embolism with spiral CT: comparison with pulmonary angiography and scin-tigraphy. Radiology 200:699–706 9. Herold CJ, Hahne J, Ghaye B et al.

(1999) Prospective evaluation of pul-monary embolism: diagnostic perfor-mance of spiral CT angiography in the ESTIPEP trial. Radiology 213(P):126– 127

10. Ghaye B, Remy J, Remy-Jardin M (2002) Non-traumatic thoracic emer-gencies: CT diagnosis of acute pulmo-nary embolism: the first 10 years. Eur Radiol DOI 10.1007/s00330–002– 1506-z

11. Goodman LR, Lipchik RJ (1996) Diag-nosis of acute pulmonary embolism: time for a new approach. Radiology 199:25–27

12. Goodman LR (2000) CT diagnosis of pulmonary embolism and deep venous thrombosis. Radiographics 20:1201– 1205

13. Carson JL, Kelley MA, Duff A et al. (1992) The clinical course of pulmona-ry embolism. N Engl J Med 326:1240– 1245

14. Fishman EK, Horton KM (2000) CT of suspected pulmonary embolism: study design optimization. Am J Roentgenol 175:1002–1003

15. Bettmann MA (1997) Venography. In: Baum S (ed) Abrams’ angiography, vol 2. Little, Brown and Company, Boston, New York, pp 1743–1754

16. Lensing AW, Kraaijenhagen R, Van Beek EJR, Buller HR (1999) Diagnosis of venous thrombosis. In: Oudkerk M, Van Beek EJR, Cate JW ten (eds) pp 44–70, Blackwell, London

17. Steele JR, Sones PJ, Heffner LT (1978) The detection of inferior vena caval thrombosis with computed tomography. Radiology 128:385–386

18. Zerhouni EA, Barth KH, Siegelman SS (1980) Demonstration of venous thrombosis by computed tomography. Am J Roentgenol 134:753–758 19. Van Breda A, Rubin BE, Druy EM

(1979) Detection of inferior vena cava abnormalities by computed tomo-graphy. J Comput Assist Tomogr 3:164–169

20. Pawar SV, Kay CJ (1984) Soft-tissue CT changes in pelvic venous thrombo-sis. Am J Roentgenol 143:605–607 21. Pagani JJ, Thomas JL, Bernardino ME

(1982) Computed tomographic mani-festations of abdominal and pelvic ve-nous collaterals. Radiology 142:415– 419

22. Vujic I, Stanley J, Tyminski LJ (1981) Computed tomography of suspected caval thrombosis secondary to proxi-mal extension of phlebitis from the leg. Radiology 140:437–441

23. Allgayer B, Reiser M, Ries G, Feuer-bach S (1981) Computed tomographic demonstration of venous thrombosis of different etiologies. Eur J Radiol 1:204–206

24. Hidalgo H, Korobkin M, Breiman RS, Heaston DK, Moore AV, Ram PC (1982) CT demonstration of subcutan-eous venous collaterals. J Comput Assist Tomogr 6:514–518

25. Pillari G, Zito J, Chang JB et al. (1987) Lower extremity swelling: computer-ized tomography following negative venography. Cardiovasc Intervent Radiol 10:261–263

26. Bauer AR, Flynn RR (1988) Computed tomography diagnosis of venous thrombosis of the lower extremities and pelvis with contrast material. Surg Gynecol Obstet 167:12–15 27. Langer B, Kauffman P, Bechara M,

Aguiar ET, Aun R (1991) Diagnosis of deep venous thrombosis of the lower limbs by computed tomography. Rev Paul Med 109:149–152

28. Stehling MK, Rosen MP, Weintraub J, Kim D, Raptopoulos V (1994) Spiral CT venography of the lower extremity. Am J Roentgenol 163:451–453 29. McLachlan MS, Thomson JG, Taylor

DW, Kelly ME, Sackett DL (1979) Ob-server variation in the interpretation of lower limb venograms. Am J Roent-genol 132:227–229

30. Picolet H, Leizorovicz A, Revel D, Chirossel P, Amiel M, Boissel JP (1990) Reliability of phlebography in the assessment of venous thrombosis in a clinical trial. Haemostasis 20:362– 367

31. Carpenter JP, Holland GA, Baum RA, Owen RS, Carpenter JT, Cope C (1993) Magnetic resonance venogra-phy for the detection of deep venous thrombosis: comparison with contrast venography and duplex Doppler ultra-sonography. J Vasc Surg 18:734–741 32. Ruehm SG, Wiesner W, Debatin JF

33. Blum JE, Handmaker H (2000) Role of small-peptide radiopharmaceuticals in the evaluation of deep venous throm-bosis. Radiographics 20:1187–1193 34. Baldt MM, Zontsich T, Stumpflen A et

al. (1996) Deep venous thrombosis of the lower extremity: efficacy of spiral CT venography compared with con-ventional venography in diagnosis. Radiology 200:423–428

35. Baldt MM, Zontsich T, Kainberger F, Fleischmann G, Mostbeck G (1997) Spiral CT evaluation of deep venous thrombosis. Semin Ultrasound CT MR 18:369–375

36. Zontsich T, Turetschek K, Baldt M (1998) CT-phlebography. A new method for the diagnosis of venous thrombosis of the upper and lower extremities. Radiologe 38:586–590

37. Gartenschlager M, Klose KJ, Schmidt JA (1996) Floating venous thrombi: diagnosis with spiral-CT-phlebography. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 164:376–381 38. Loud PA, Katz DS, Klippenstein DL,

Shah RD, Grossman ZD (2000) Com-bined CT venography and pulmonary angiography in suspected thromboem-bolic disease: diagnostic accuracy for deep venous evaluation. Am J Roent-genol 174:61–65

39. Ghaye B, Szapiro D, Willems V, Dondelinger RF (2000) Combined CT venography of the lower limbs and spi-ral CT angiography of pulmonary arte-ries in acute pulmonary embolism: pre-liminary results of a prospective study. JBR-BTR 83:271–278

40. Garg K, Kemp JL, Wojcik D et al. (2000) Thromboembolic disease: com-parison of combined CT pulmonary angiography and venography with bi-lateral leg sonography in 70 patients. Am J Roentgenol 175:997–1001 41. Cham MD, Yankelevitz DF, Shaham D

et al. (2000) Deep venous thrombosis: detection by using indirect CT veno-graphy. Radiology 216:744–751 42. Yankelevitz DF, Gamsu G, Shah A et

al. (2000) Optimization of combined CT pulmonary angiography with lower extremity CT venography. Am J Roentgenol 174:67–69

43. Garg K, Kemp JL, Russ PD, Baron AE (2001) Thromboembolic disease: vari-ability of interobserver agreement in the interpretation of CT venography with CT pulmonary angiography. Am J Roentgenol 176:1043–1047 44. Garg K, Mao J (2001) Deep venous

thrombosis: spectrum of findings and pitfalls in interpretation on CT veno-graphy. Am J Roentgenol 177:319–323

45. Vogelzang RL, Gore RM, Anschuetz SL, Blei AT (1988) Thrombosis of the splanchnic veins: CT diagnosis. Am J Roentgenol 150:93–96

46. Lien HH, Lund G (1983) Collateral veins in inferior caval vein occlusion demonstrated via CT. Eur J Radiol 3:319–323

47. Seem E, Stranden E, Stiris MG (1985) Computed tomography in deep venous thrombosis with limb oedema. Acta Radiol Diagn 26:727–730

48. Duwe KM, Shiau M, Budorick NE, Austin JH, Berkmen YM (2000) Evalu-ation of the lower extremity veins in patients with suspected pulmonary em-bolism: a retrospective comparison of helical CT venography and sonogra-phy. Am J Roentgenol 175:1525–1531 49. Ghaye B, Szapiro D, Willems V,

Dondelinger RF (2002) Pitfalls in CT venography of the lower limbs and ab-dominal veins. Am J Roentgenol 178:1465–1471

50. Gmelin E, Link J, Judaschke S, Marienhoff N (1992) Non-enhanced CT of thrombosed calf veins. Rofo Fortschr Geb Rontgenstr Neuen Bild-geb Verfahr 156:338–341

51. Loud PA, Katz DS, Bruce DA, Klippen-stein DL, Grossman ZD (2001) Deep venous thrombosis with suspected pul-monary embolism: detection with com-bined CT venography and pulmonary angiography. Radiology 219:498–502 52. Hull RD, Carter CJ, Jay RM et al.

(1983) The diagnosis of acute, recur-rent, deep-vein thrombosis: a diagnos-tic challenge. Circulation 67:901– 906

53. Cronan JJ, Leen V (1989) Recurrent deep venous thrombosis: limitations of US. Radiology 170:739–742 54. Coche EE, Hamoir XL, Hammer FD,

Hainaut P, Goffette PP (2001) Using dual-detector helical CT angiography to detect deep venous thrombosis in patients with suspicion of pulmonary embolism: diagnostic value and addi-tional findings. Am J Roentgenol 176:1035–1039

55. Abdelmoumene U, Portier F, Wicky S, Schnyder P, Denys A (2001) Optimiza-tion of venous enhancement in multi-detector CT by wearing compressive stockings. J Radiol 82:1264

56. El Hajjam M, Qanadli SD, Mignon F, Sissakian J, Chagnon S, LaCombe P (1999) Combined double helical CT phlebography of the lower extremities and CT pulmonary angiography: new approach for thromboembolic disease diagnosis. Radiology 213 (Suppl):126 57. Muller C, Kopka L, Funke M,

Funke C, Grabbe E (2001) Diagnosis of lung embolism and underlying ve-nous thrombosis in multi-slice spi-ral CT. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 173:528–535

58. Nicolas M, Debelle L, Laurent V et al. (2001) Incremental lower extremity CT venography, a simplified approach for the diagnosis of deep venous thrombo-sis in patients with pulmonary embo-lism. J Radiol 82:251–256

59. Schoepf UJ, Kessler MA, Rieger CT et al. (2001) Multislice CT imaging of pulmonary embolism. Eur Radiol 11:2278–2286

60. Szapiro D, Ghaye B, Willems V, Zhang L, Albert A, Dondelinger RF (2001) Evaluation of CT time–density curves of lower-limb veins. Invest Radiol 36:164–169

61. Rademaker J, Griesshaber V, Hidajat N, Oestmann JW, Felix R (2001) Com-bined CT pulmonary angiography and venography for diagnosis of pulmonary embolism and deep vein thrombosis: radiation dose. J Thorac Imaging 16:297–299

62. Lomas DJ, Britton PD (1991) CT dem-onstration of acute and chronic ilio-femoral thrombosis. J Comput Assist Tomogr 15:861–862

63. Matar LD, Ramirez JA, McAdams HP, Farrell MA, Herndon JE (1999) Opti-mal timing of CT venography follow-ing CT pulmonary angiography usfollow-ing a multidetector row helical scanner: work in progress. Radiology 213 (Suppl):472–473

64. Bruce D, Loud PA, Klippenstein DL, Grossman ZD, Katz DS (2001) Com-bined CT venography and pulmonary angiography: How much venous en-hancement is routinely obtained? Am J Roentgenol 176:1281–1285 65. Youssefzadeh S, Liskutin J,

Do-rffner R, Bankier A, Hubsch P (1998) Venous contrast fluid level in comput-ed tomography. Clin Radiol 53:528– 531

66. Wagner M, Mark L (1969) Duplication of the inferior vena cava and its role in recurrent pulmonary emboli. J Am Med Assoc 209:108–109

67. Kouroukis C, LeClerc JR (1996) Pul-monary embolism with duplicated infe-rior vena cava. Chest 109:1111–1113 68. Katz DS, Loud PA, Klippenstein DL, Shah RA, Grossman ZD (2000) Extra-thoracic findings on the venous phase of combined computed tomographic venography and pulmonary angiogra-phy. Clin Radiol 55:177–181 69. Glazer GM, Callen PW, Parker JJ

(1981) CT diagnosis of tumor throm-bus in the inferior vena cava: avoiding the false-positive diagnosis. Am J Roentgenol 137:1265–1267 70. Barnes PA, Bernardino ME, Thomas

71. Vogelzang RL, Gore RM, Neiman HL, Smith SJ, Deschler TW, Varla RF (1985) Inferior vena cava CT pseudo-thrombus produced by rapid arm-vein contrast infusion. Am J Roentgenol 144:843–846

72. Yankelevitz DF, Cham MD, Shaham D, Henschke CI (2000) Common diagnos-tic pitfalls of indirect CT venography. Radiology 217 (Suppl):127

73. Ciccotosto C, Goodman LR, Washington L, Quiroz FA (2002) Indirect CT ve-nography following CT pulmonary angiography: spectrum of findings. J Thorac Imaging 17:18–27

74. Censullo ML, Ernst RD, Kawashima A, Caskey CI, Sandler CM (1999) CT venography as an adjunct to CT pul-monary angiography for the detection of pulmonary thrombo-embolic dis-ease. Radiology 213 (Suppl):558

75. Balakrishnan C, Gheiler EL (1993) Computed tomography for diagnosis of deep venous thrombosis in burn pa-tients. Plast Reconstr Surg 91:1174– 1175

76. Delalu P, Ferretti GR, Bricault I, Ayanian D, Coulomb M (2000) Para-doxical emboli: demonstration using helical computed tomography of the pulmonary artery associated with ab-dominal computed tomography. Eur Radiol 10:384–386

77. Wildberger JE, Mahnken AH, Sinha AM, Haage P, Schaller S, Gunther RW (2002) A differentiated approach to pulmonary embolism and deep venous thrombosis using multi-slice CT. Eur Radiol 12 (Suppl):262

78. Ciccotosto C, Filippone A, Storto ML, Ricciardi M, Salcuni M, Bonomo L (2002) Accuracy of multislice CT for acute deep venous thrombosis: vari-ability of observer performance related to clinical experience. Eur Radiol 12 (Suppl):150

79. Landragin E, Delval O, Corneloup O, Tallon JB, Morin M, Vandermarcq P (2001) Can CT venography replace US in the diagnosis of deep venous throm-bosis? J Radiol 82:1444

80. Jonetz-Mentzel L, Basche S, Eger C (2001) CT phlebography and CT angio-graphy of the pulmonary arteries in the diagnosis of acute lung embolism. Eur Radiol 11 (Suppl):137

81. Ferretti GR, Ayanian D, Ranchoup Y, Thony F, Bosson JL, Coulomb M (1998) CT assessment of abdominal and pelvic veins in patients suspected of acute pulmonary embolism and pre-senting with normal sonography of the lower limbs. J Radiol 79:327–330 82. Au VW, Walsh G, Fon G (2001)