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(Chest. 2005;127:1606-1613.)
© 2005 American College of Chest Physicians

CT Scan Findings in Chronic Thromboembolic Pulmonary Hypertension*

Predictors of Hemodynamic Improvement After Pulmonary Thromboendarterectomy

Marc Heinrich, MD; Michael Uder, MD; Dietmar Tscholl, MD; Aleksandar Grgic, MD; Bernhard Kramann, MD and Hans-Joachim Schäfers, MD, FCCP

* From the Departments of Diagnostic Radiology (Drs. Heinrich and Kramann) and Thoracic and Cardiovascular Surgery (Drs. Tscholl and Schäfers), University Hospital of Saarland, Homburg/Saar, Germany; and the Department of Diagnostic Radiology (Dr. Uder), University Hospital of Erlangen, Erlangen, Germany.

Correspondence to: Hans-Joachim Schäfers, MD, FCCP, Department of Thoracic and Cardiovascular Surgery, University Hospitals Homburg/Saar University of Saarland, Kirrberger Str, D-66421 Homburg/Saar, Germany; e-mail: chhjsc{at}uniklinik-saarland.de


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: The aim was to correlate CT scan findings with hemodynamic measurements in patients who had undergone pulmonary thromboendarterectomy (PTE) and to evaluate whether CT scan findings can help to predict surgical outcome.

Patients and method: Sixty patients who underwent PTE and preoperative helical CT scanning were included. Preoperative and postoperative hemodynamics were correlated with preoperative CT imaging features.

Results: The diameter of the main pulmonary artery (PA) and the ratio of the PA and the diameter of the ascending aorta correlated with preoperative mean pulmonary artery pressure (PAP) [r = 0.42; p < 0.001; and r = 0.48; p < 0.0001, respectively]. There was a significant correlation of subpleural densities with preoperative pulmonary vascular resistance (PVR) [r = 0.44; p < 0.001] and of the number of abnormal perfused lobes with preoperative PAP (r = 0.66; p < 0.0001) and PVR (r = 0.76; p < 0.0001). Postoperative PVR correlated negatively with the presence and extent of central thrombi (r = –0.36; p = 0.007) and dilated bronchial arteries (p = 0.03) seen on preoperative CT scans. Sixty percent of patients (3 of 5 patients) without visible central thromboembolic material on CT scans had an inadequate hemodynamic improvement in contrast to 4% of patients (2 of 51 patients) with central thrombi (p = 0.003). Preoperative PVR (r = 0.31; p = 0.018) and the extent of abnormal lung perfusion (r = 0.37; p = 0.007) and of subpleural densities (r = 0.32; p = 0.017) were positively correlated with postoperative PVR.

Conclusions: In patients with thromboembolic pulmonary hypertension, CT scan findings can help to predict hemodynamic improvement after PTE. The absence of central thrombi is a significant risk factor for inadequate hemodynamic improvement.

Key Words: endarterectomy • pulmonary hypertension • pulmonary embolism • retrospective studies • spiral CT scan


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Chronic thromboembolic pulmonary hypertension (CTEPH) has been considered to be a rare complication of pulmonary embolism. It was, however, recently demonstrated1 that the occurrence of symptomatic CTEPH after pulmonary embolism is more common than previously thought, with a cumulative incidence of 3.8%. The etiology of CTEPH includes the incomplete resolution and organization of pulmonary emboli. These can be completely incorporated into the vascular wall and can lead to obstruction or stenosis of the pulmonary arteries. Additionally, remodeling of the primarily unaffected pulmonary arteries will occur over time, resulting in a vasculopathy of precapillary vessels similar to the arteriopathy found in patients with primary pulmonary hypertension (PPH) and pulmonary hypertension.234 CTEPH is associated with a poor prognosis, which depends on the severity of pulmonary hypertension. If the mean pulmonary artery pressure (PAP) exceeds 30 mm Hg, the 5-year survival rate is only 30%.56

Pulmonary thromboendarterectomy (PTE), which appears to be permanently curative in the majority of the cases, is the treatment of choice for CTEPH.57 The location and proximal extent of the thromboembolic changes are considered to be crucial in determining operability.89 It is generally thought that organized thrombi should be present at the level of the main or lobar arteries, or at the origin of the segmental vessels to safely create a dissection plane.49

Decision making for or against PTE can be difficult in these patients. Traditionally, the surgeon attempts to differentiate between the proximal, surgically accessible component of the scar tissue and the surgically inaccessible disease or secondary small-vessel arteriopathy.58 Despite careful diagnostic workup and decision making in all of these patients, the mortality rate after PTE is still approximately 10%,781011 and the persistence of high pulmonary vascular resistance (PVR) is seen in most of these patients.5 In addition, about 10 to 15% of the patients show persistent pulmonary hypertension, probably due to distal arteriopathy.211

Pulmonary angiography still is considered to be the "gold standard" for the evaluation of CTEPH and for assessing operability.47 Angiography, however, is an invasive method, and the interpretation of these angiograms can be difficult in patients with CTEPH.4 Over the past few years, CT scanning has proven its diagnostic value in cases of acute pulmonary embolism.12131415 It has also been proposed as a reliable and less invasive tool for the diagnosis of CTEPH.161718 While CT scanning appears to be helpful in establishing the diagnosis, its role in the preoperative evaluation of patients with CTEPH remains incompletely defined.79 It is unclear whether operability and surgical success, defined as mortality and/or improvement of PVR, can be predicted by CT scan parameters with sufficient accuracy.

The aim of the present study was to correlate preoperative CT scan findings in patients who have undergone PTE with preoperative and postoperative hemodynamics, and to evaluate whether CT scanning can identify patients who are at high risk for insufficient hemodynamic improvement after surgery.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Patients
Sixty consecutive patients (31 men, 29 women) with an average age of 54 years (age range, 18 to 79 years) were included in this retrospective study, and underwent PTE for CTEPH and a CT scan of the chest at our institution between May 1996 and September 2002. Preoperatively, all patients underwent additional left and right heart catheterization and pulmonary angiography. Right atrial pressure, PAP, and pulmonary wedge pressure were measured. Cardiac output was determined by thermodilution, and PVR was calculated. All operations were performed by the same surgeon using a technique that has previously been described.11 Postoperative hemodynamic measurements were performed before Swan-Ganz catheter removal. Postoperative PVR was available in 58 patients and was used to determine surgical outcome.

Helical CT Scan
A helical CT scan of the chest was performed using a single-slice CT scanner (Somatom Plus-S; Siemens; Erlangen, Germany) or a four-row multidetector CT unit (MX8000; Philips Medical Systems; Hamburg, Germany) with a collimation of 2.5 to 5 mm, an increment of 1.6 to 5 mm, and a pitch of 1.5 to 2.0. The whole chest was scanned during a single breathhold. One hundred twenty milliliters of the nonionic, monomeric contrast medium iomeprol with a concentration of 300 mg I/mL (Imeron 300; Bracco-Byk Gulden; Konstanz, Germany) was administered by a power injector, in some patients followed by a saline solution flush of 30 to 50 mL, with an injection rate of 2.5 to 3.5 mL/s. Scan delays varied between 20 and 30 s depending on cardiac function, location, and size of the IV line, and the duration of the CT scan. CT scans obtained images at the mediastinal window setting (level, 50 Hounsfield units [HU]; width, 350 HU) and the lung window setting (level, –500 HU; width, 1,500 HU).

Image Interpretation
Two radiologists, who were blinded to the hemodynamic measurements and the surgical outcome, interpreted axial images of the CT scans on hard copies in consensus. The widest diameter of the ascending aorta (AO) and the widest diameter of the main pulmonary artery (PA) perpendicular to its long axis were measured at the level of the bifurcation of the pulmonary artery, and the ratio of the main pulmonary artery and AO was determined (rPA) [n = 60]. The outer limits of the contrast were used to determine vessel diameter on the IV contrast medium-enhanced CT scans.

The presence of thromboembolic disease in the central arteries was evaluated. Central, surgically accessible arteries were defined as vessels that were proximal to the segmental arteries. The presence of central disease was assumed if thrombi, thromboembolic material lining the vessel wall, or irregularities of the intimal surface were observed.

On axial images obtained at mediastinal window settings, the central thromboembolic material was quantified using a modified index described by Qanadli et al.19 In three patients, the scoring of thrombi was not possible because of insufficient contrast media enhancement of the pulmonary arteries or missing CT scans (n = 57). In contrast to the original index, which was evaluated in patients with acute pulmonary emboli, we scored only the thromboembolic material in the central arteries. The index was defined as n x d, where n is the value of the proximal thrombus site, equal to the number of segmental branches arising distally, and d is the degree of obstruction, defined as 1, when partially occlusive thrombus was observed, and 2 for total occlusion. So, the maximal obstruction index was 40 for each patient. This score was converted into a percentage by dividing the patient score by the maximal total score and by multiplying the result by 100 ({sum}[n x d]/40 x 100).

The CT scans were evaluated to assess dilated bronchial arteries. Bronchial arteries were considered to be dilated if their diameters were ≥ 1.5 mm.20 The evaluation of bronchial arteries was not possible in nine patients because of insufficient imaging quality or missing films (n = 51).

CT scan images at lung window settings were analyzed for peripheral, irregular, wedge-shaped, or linear densities, possibly representing residual densities from prior infarctions. To quantify the peripheral densities, we added the number of involved lobes (lingula was regarded as a lobe, score 0 to 6). In three patients, the assessment of peripheral densities was not possible because of missing CT scans obtained at lung window settings (n = 57).

The abnormal perfusion of the lobes was evaluated on images obtained at lung window settings. The perfusion of the lobes was considered to be abnormal if the lung parenchyma was inhomogeneous or of relatively low attenuation, or if segmental vessel size was diminished or varying. We quantified the abnormal lung perfusion by adding the number of lobes with abnormal perfusion (score, 0 to 6). Lung perfusion scoring was not possible in seven patients because of artifacts resulting from respiration or because of missing CT scans at lung window settings (n = 53).

Statistical Analysis
For statistical analysis and graphic representation, a statistical software package (SPSS, version 11.5 for Windows; SPSS; Chicago, IL) was used. All data were given as the mean ± SD. Comparisons of CT findings with hemodynamic measurements were performed by univariate and multivariate analysis. Patients with postoperative PVR of ≥ 500 dyne · s · cm–5 were considered to have insufficient hemodynamic improvement and to have not benefited from surgery. The univariate analyses for continuous variables were performed by t test or nonparametric Mann-Whitney test and nonparametric Spearman rank correlation. Nominal variables were analyzed by cross-tabulations and Fisher exact test. Multivariate analysis was performed by multiple linear stepwise regression analysis.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Correlation With Preoperative Hemodynamics
The preoperative PAP ranged from 24 to 80 mm Hg (mean, 47 ± 12 mm Hg). The mean preoperative PVR was 906 ± 422 dyne · s · cm–5 (range, 267 to 1938 dyne · s · cm–5). The PA ranged from 2.5 to 5.3 cm (mean diameter, 3.9 ± 0.55 cm). Ninety-eight percent of patients showed a pulmonary artery size of ≥ 3 cm. The mean rPA was 1.14 ± 0.2 (range, 0.84 to 1.85). One of 60 patients had a PAP of < 25 mm Hg. In this patient, the rPA was 0.84. In 86% of patients with a PAP of > 20 mm Hg, the rPA was ≥ 1.

The univariate correlation of CT scan findings with preoperative PAP and PVR are summarized in Table 1 . The PA and the rPA showed a significant correlation with PAP, whereas the correlation with preoperative PVR was only weak or not significant. In 91.4% of patients (53 of 58 patients), central thromboembolic material was detectable. There were no significant differences of preoperative PAP or PVR between patients with and without the depiction of central thrombi (PAP, 47 ± 12 vs 45 ± 6 mm Hg, respectively; PVR, 891 vs 1,050 ± 512 dyne · s · cm–5, respectively; p > 0.05). The mean score of central thrombi was 37 ± 21% (range, 0 to 85%). The score of central thromboembolic material showed a significant correlation with neither PAP nor PVR. Dilated bronchial arteries could be demonstrated in 47.1% of patients (Fig 1 ). The mean preoperative PAP and PVR were not significantly different in patients with and without dilated bronchial arteries (PAP, 44 ± 12 vs 50 ± 11 mm Hg, respectively; PVR, 817 ± 419 vs 986 ± 427 dyne · s · cm–5; p > 0.05). Peripheral densities were seen in 87.7% of patients (Fig 2 ). The number of lobes with peripheral densities (scar score) demonstrated a poor correlation with PAP and a moderate correlation with PVR (mean score, 2.28 ± 1.46; range, 0 to 6). All patients showed at least two lobes with abnormal perfusion. The best parameter for correlation with preoperative hemodynamic measurements was the number of lobes with abnormal perfusion (perfusion score), which demonstrated a strong correlation with PAP and PVR (mean score, 5.17 ± 1.24; range, 2 to 6) [Fig 3 ]. In multiple linear regression analysis, including all evaluated CT scan findings, the perfusion score correlated with the PAP and mean PVR (PAP, 13.82 + 6.48 x perfusion score; R = 0.60; p < 0.0001; PVR: –397.98 + 257.33 x perfusion score; R = 0.67; p < 0.0001).


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  		Table 1.. Correlation of CT Scan Findings With Preoperative Hemodynamics

 


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  		Figure 1.. Contrast-enhanced CT scan in a patient with CTEPH shows bronchial artery collaterals. Note that the enlarged main pulmonary artery has a larger diameter than the AO.

 


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  		Figure 2.. CT scan in a patient with CTEPH shows a pleura-based wedge-shaped scar in the right upper lobe caused by prior infarction.

 


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  		Figure 3.. Correlation of perfusion score and preoperative PVR.

 
Correlation With Postoperative PVR
Mean postoperative PVR was 290 ± 181 dyne · s · cm–5 (range, 69 to 1,058 dyne · s · cm–5). Univariate correlation of CT findings with postoperative PVR is summarized in Table 2 . Preoperative PVR demonstrated a significant correlation with postoperative PVR. Neither the PA nor the rPA showed a significant correlation with postoperative PVR. Postoperative PVR was significantly lower in patients with central thromboembolic material visible on CT scan compared to patients without visible central thrombi (265 ± 143 vs 575 ± 305 dyne · s · cm–5; p = 0.008). Three of five patients (60%) without central thromboembolic material visible on CT scan had an inadequate hemodynamic improvement in contrast to 2 of 51 patients (4%) with central thrombi (p = 0.003). The score of central thromboembolic material showed a significant negative correlation with postoperative PVR. The score of peripheral densities correlated positively with the postoperative PVR. The mean postoperative PVR was significantly lower in patients with dilated bronchial arteries than in patients without (221 ± 79 vs 318 ± 206 dyne · s · cm–5; p = 0.03). The score of lung perfusion showed a significant positive correlation with postoperative PVR.


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  		Table 2.. Correlation of CT Scan Findings With Postoperative PVR

 
The analysis of postoperative PVR demonstrated five patients to be "outliers" with PVR values of > 500 dyne · s · cm–5 (Fig 4 ). The multivariate analysis of the correlation of CT scan findings with postoperative PVR, including all evaluated CT scan findings and preoperative PVR, was performed by multiple linear regression analysis in all patients and after exclusion of the 5 "outliers" with postoperative PVR of > 500 dyne · s · cm–5. In a multivariate analysis of all patients, the presence of central thromboembolic material and the score of peripheral densities were shown to be significant predictors of postoperative PVR (ie, post-operative PVR = 461 – 285 x thrombus + 36 x scar score; R = 0.55; p < 0.001). After the exclusion of the five patients with a postoperative PVR of > 500 dyne · s · cm–5, the central thrombi score and lung perfusion score were significant predictors of postoperative PVR (postoperative PVR = 210 – 2 x thrombi score + 20 x perfusion score; R = 0.54; p = 0.003).



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  		Figure 4.. Box-and-whisker plot of the PVR. There are five outliers with postoperative PVR values of > 500 dyne · s · cm–5.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
PTE has been repeatedly shown to be effective in patients with CTEPH, resulting in marked improvement of symptoms and pulmonary hemodynamics.51011 Despite its potential role as causative therapy, CTEPH is still associated with a mortality rate of 10% and fails to significantly reduce PVR in an additional 10 to 15% of the patients.11 In view of these results, most patients undergo a careful diagnostic evaluation before the decision for or against surgery is made. Pulmonary angiography has been regarded as the diagnostic "gold standard," even though its interpretation may be difficult in patients with this disease.47 Angioscopy has not found wide acceptance. Both methods, however, have not provided reliable predictors of surgical success (ie, they have not been able to identify patients who are at high risk for the persistence of pulmonary hypertension preoperatively). Initially, CT scanning was used primarily to identify thrombi in the central pulmonary arteries, which has been considered as a criterion for the operability of CTEPH. More recently, it has been found that CT scanning provides more information on different components of the disease, predicting surgical success in the individual patient.2021

The degree of postoperative residual PVR is the factor, which most strongly correlates with mortality. In one study,5 patients with a postoperative PVR of > 500 dyne · s · cm–5 had a mortality rate of 30.6% compared to a mortality rate of 0.9% in patients with a postoperative PVR of < 500 dyne · s · cm–5. Thus, we used postoperative PVR as the parameter for determining surgical success; patients with a postoperative PVR > 500 dyne · s · cm–5 were considered not to have benefited from surgery.

The presence of thromboembolic changes in the central pulmonary arteries has been one of the key features of CTEPH. In interpreting these manifestations, one has to consider the pathologic nature of this central disease. In our study, the presence and extent of central thromboembolic disease as assessed by CT scan correlated negatively with postoperative PVR. The absence of central disease on the CT scan was associated with a higher risk of inadequate hemodynamic improvement after surgery. Two previous studies2122 have already demonstrated that patients with more extensive central disease seen on CT scans had lower postoperative PVR values than patients with less extensive central changes. This is in agreement with a clinical study23 based on operative findings in which patients without central thromboembolic disease had higher postoperative PVR values and perioperative mortality rate than patients with central changes.

Interestingly, in our study two patients with central thromboembolic disease showed inadequate hemodynamic improvement. On the other hand, two patients without evidence of central disease had a good hemodynamic response to surgery. It is also notable that the presence of central material showed no significant correlation with preoperative PVR or PAP, and therefore the presence of central thrombi did not predict the degree of pulmonary hypertension. These findings confirm previous observations that the detection of central thromboembolic changes does not ensure surgical success and that their absence does not necessarily predict an inadequate surgical outcome.24 The reasons for this discrepancy between surgical results and the presence of central thrombus have not been clarified. It has been proposed that factors other than major vessel occlusion contribute to the development of pulmonary hypertension.4 A secondary precapillary vasculopathy developing over time in the unobstructed lung regions as well as its occurrence distal to the occluded proximal pulmonary arteries is thought to play an important role in this process.24 On the other hand, one has to keep in mind that the obstruction of pulmonary arteries in patients with CTEPH is primarily caused by scar tissue, which develops through the organization of the original fresh thrombi. It has been our impression that some of the CT scan changes in the proximal pulmonary arteries are caused by a chronic thrombus overlying the obstructing scar tissue. The removal of scar tissue rather than removal of the chronic thrombus has been shown to be the important part of the surgical procedure. Scar tissue, on the other hand, can exist without a superimposed thrombus, which explains the surgical success in the absence of CT scan morphology that is consistent with central disease. Finally, thrombi have also been observed in patients with PPH.25

Thus, it appears reasonable to assume that the presence of central thromboembolic changes does not accurately predict the degree of mechanical obstruction of the pulmonary arteries. The high incidence of central thrombotic material in our patient cohort and other observations may simply be due to the fact that this CT scan morphology is suggestive of CTEPH and more often leads to its diagnosis.

Since the physiologically important component of pulmonary vascular obstruction may be difficult to visualize directly, the assessment of pulmonary parenchymal perfusion appears to be a reasonable parameter. We quantified the abnormality of lung perfusion by adding the number of lobes with abnormal perfusion. Lobes were regarded as abnormally perfused when the lung parenchyma was inhomogeneous or of relatively low attenuation, or if the segmental vessel size was diminished or varying (ie, mosaic oligemia). All patients demonstrated lobes with abnormal perfusion. This is consistent with the findings of previous studies,26272829 which demonstrated a mosaic pattern of lung attenuation in 77 to 100% of patients with CTEPH.

In patients with CTEPH, the areas of decreased attenuation represent the hypoperfused lung zones.2829 This could explain the good correlation of the number of abnormally perfused lobes seen on CT scans with the preoperative PVR as a sign for the severity of the disease. A high preoperative PVR is a well-known risk factor for the postoperative improvement of PVR.511 Independent of its correlation with preoperative PVR, the number of abnormally perfused lobes was also a predictor for postoperative PVR by means of multivariate analysis in our study. A high number of abnormally perfused lobes correlated with a higher postoperative PVR. Possibly this is due to the fact that patients with a high number of abnormally perfused lobes, as assessed by CT scan, have a high number of lobes in which small-vessel disease could be present, whereby patients have less benefit from a central revascularization. A previous study21 demonstrated that an extensive mosaic perfusion pattern in the presence of normal segmental arteries was associated with a relatively high postoperative PVR. The authors suggested that this was due to small-vessel disease. In contrast to these results, no correlation between the presence of a mosaic perfusion pattern with either normal or abnormal segmental arteries and the postoperative PVR was found in a recent study.22 The attenuation differences due to the occlusion of medium-sized and small-sized pulmonary arteries may be subtle and close to the limit of visual detection.30 We would suggest that the evaluation of a mosaic pattern of lung attenuation on a segmental level, such as was done in the study by Oikonomou et al,22 is less reliable than evaluation on a lobar level, as was done in our study.

In our study, 87% of patients showed peripheral densities. This is comparable with the results of a previous study,27 in which 59 to 82% of patients with CTEPH had peripheral densities in contrast to only 22 to 26% of non-CTEPH patients. Subpleural, often wedge-shaped opacities are a well-known finding in patients with pulmonary emboli313233 and are commonly seen on the CT scans of patients with CTEPH, probably due to prior infarction.1828 With increasing age, the appearance of pulmonary infarctions can shift to irregular opacities because of scarring.34

The peripheral densities showed a significant correlation with preoperative PVR in our study. Additionally, the peripheral densities correlated significantly with postoperative PVR, independently of the correlation with the preoperative PVR by means of multivariate analysis. Pulmonary infarction is uncommon when central arteries are obstructed, but is frequent when distal arteries are occluded.35 Therefore, we suggest that patients who had multiple peripheral densities, which were probably due to prior infarctions, had a greater number of occluded distal arteries, which are surgically incompletely accessible, leading to higher preoperative and postoperative PVR values compared to patients with fewer peripheral infarctions.

Dilated bronchial arteries were seen in 47% of our patients. This is consistent with previous studies of CT scans,203637 which demonstrated dilated bronchial arteries in 47 to 51% of patients with CTEPH. The presence of dilated bronchial arteries can help to distinguish patients with CTEPH from patients with acute PE or PPH, in which dilated bronchial arteries are only rarely present.363738

There was no significant difference between patients with and without dilated bronchial arteries regarding preoperative hemodynamics. An earlier study20 already found no significant differences in PAP between patients with and without the depiction of bronchial arteries seen on CT scans. This suggests that elevation of PAP per se is not the stimulus for the development of dilated bronchial arteries. Other factors, for instance, the localization of the thromboembolic occlusion, must play a role.

Postoperative PVR was significantly lower in patients with dilated bronchial arteries than in patients without. Kauczor et al20 found evidence for a lower postoperative mortality rate in patients with dilated bronchial arteries after PTE compared to patients without dilated arteries. We would suggest that patients without dilated bronchial arteries have a higher degree of distal vascular disease, due either to distal thromboembolic material or to secondary small-vessel disease, leading to a higher postoperative PVR compared to patients with dilated bronchial arteries. This hypothesis is supported by an animal study39 that demonstrated that the increase in number and enlargement of bronchopulmonary anastomoses were more pronounced after proximal occlusion of the left diaphragmatic lobar pulmonary artery than after distal occlusion. If in patients with proximal CTEPH the small distal arteries and arterioles are unaffected, this would increase the pressure gradient between the systemic circulation and the pulmonary circulation distal to the blockage, allowing an increase in bronchopulmonary blood flow and the development of bronchopulmonary collateral supply.38 In contrast, the small arteries and arterioles are primarily affected in patients with PPH, in whom no bronchopulmonary collaterals were observed.38

The dilation of the main pulmonary artery is a common finding in patients with pulmonary hypertension. The presence of a dilated pulmonary artery can readily predict pulmonary hypertension.404142 Schmidt et al43 studied patients with CTEPH and demonstrated a significant correlation of the PA with PAP (r = 0.43), but not with PVR. These results are similar to those in our study (r = 0.42 [PA vs PAP]; there was no significant correlation with PVR). The rPA showed a slightly better correlation with PAP compared to the PA. This observation has to be interpreted carefully, because Ng et al40 demonstrated that in patients with a wide range of pulmonary and cardiovascular diseases the PA was influenced by the body surface area, whereas the rPA was confounded by age. The authors suggested the dependency of rPA, but not the PA, on age to reflect a gradual increase in aortic diameter with age. In their study, PAP correlated more strongly with rPA than with the PA in patients < 50 years of age, whereas the correlation with the PA was stronger in patients > 50 years of age.40 The PA and the rPA may be useful to support the diagnosis of pulmonary hypertension, but only provide a rough estimation. Most importantly, the PA and the rPA did not predict postoperative hemodynamics.

Some limitations of our study have to be considered. The retrospective design of our study allows for less generalization from our results. Furthermore, there was a strong selection bias because only patients who underwent PTE were included in our study. Moreover, there was only a small number of patients with a postoperative PVR of > 500 dyne · s · cm–5, making a multivariate analysis of this group of patients impossible and leading to a limited value for the statistical analysis. Because of the retrospective study design, there was no standardized CT scan protocol. The evaluation of the CT scans was possible to perform only on hard copies, and no postprocessing images (eg, maximum intensity projections) were available.

The correlation of CT scan findings with preoperative hemodynamics in patients with CTEPH showed that CT scanning is useful to estimate the severity of the disease. Moreover, a combination of different relatively simple-to-assess CT scan scores can help to predict hemodynamic improvement after PTE. However, the performance of a prospective study with more recent CT scan technology is necessary to evaluate whether CT scanning can predict surgical outcome in all patients. With the new ≥ 16-row multidetector CT scan technology, it is possible to cover the entire chest with submillimeter collimation in a single breathhold, facilitating maximum intensity projections, multiple planar reformations, and curved planar reformations of the highest quality due to isotropic voxels, which markedly improve the evaluation of the pulmonary vessels. New CT scan technology using these postprocessing modalities may be the answer for the existing diagnostic problems in patients with CTEPH, and they may be able to replace the other imaging modalities, including perfusion scanning and pulmonary angiography.


   Footnotes
 
Abbreviations: AO = ascending aorta; CTEPH = chronic thromboembolic pulmonary hypertension; HU = Hounsfield units; PA = diameter of the main pulmonary artery; PAP = mean pulmonary artery pressure; PPH = primary pulmonary hypertension; PTE = pulmonary thromboendarterectomy; PVR = pulmonary vascular resistance; rPA = ratio of the main pulmonary artery and ascending aorta

All authors have no direct or indirect financial interest in the products under investigation or subject matter discussed in this article.

Received for publication September 23, 2004. Accepted for publication November 17, 2004.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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