Pulmonary Hypertension: CT of the Chest in Pulmonary Venoocclusive Disease
Abstract
OBJECTIVE. Pulmonary venoocclusive disease is a rare cause of pulmonary hypertension that is often difficult to distinguish from severe primary pulmonary hypertension. Unfortunately, medical treatment of primary pulmonary hypertension with prostacyclin can be fatal in patients with venoocclusive disease, and an early pretreatment diagnosis of this uncommon condition is critical. The aim of our study was to evaluate this disease noninvasively using CT of the chest.
MATERIALS AND METHODS. We reviewed cross-referenced records from 1996 to 2001 in our departments of radiology and pathology and identified 15 patients with initial pretreatment CT scans who had pathologically confirmed pulmonary venoocclusive disease. Their CT scans were compared with the CT scans of 15 consecutive patients with pathologically confirmed primary pulmonary hypertension. All patients had undergone a postmortem or posttransplantation examination.
RESULTS. Ground-glass opacities were significantly more frequent in pulmonary venoocclusive disease (p = 0.003); the opacities were abundant with random zonal predominance and preferentially centrilobular distribution (p = 0.03). Subpleural septal lines and adenopathy were also significantly more frequent (p < 0.0001).
CONCLUSION. On the initial pretreatment chest CT scan, the presence of ground-glass opacities (particularly with a centrilobular distribution), septal lines, and adenopathy are indicative of pulmonary venoocclusive disease in patients displaying pulmonary hypertension. Caution should be exercised before vasodilator therapy is initiated in the patients whose scans show such radiologic abnormalities.
Introduction
Pulmonary venoocclusive disease is a rare cause of pulmonary hypertension that preferentially affects the postcapillary (venous) pulmonary vasculature [1]. This disease poses diagnostic and treatment dilemmas. Indeed, patients with pulmonary venoocclusive disease frequently present in a similar fashion as those with other forms of pulmonary hypertension, particularly primary pulmonary hypertension [2]. Continuous IV infusion of prostacyclin (PGI2 or epoprostenol) or, most recently, inhalation of an aerosolized prostacyclin analogue (iloprost) [3, 4] are effective treatments for primary pulmonary hypertension [5, 6]. Unfortunately, these vasodilator therapies can be harmful and occasionally fatal in patients with pulmonary venoocclusive disease. Fulminant pulmonary edema has been reported with the use of prostacyclin [7–9]. It is therefore critical for clinicians to distinguish pulmonary venoocclusive disease from primary pulmonary hypertension.
Histopathologic diagnosis of pulmonary venoocclusive disease cannot generally be made by examination of transbronchial biopsy specimens, and an open biopsy is required. Because of the weakness of these patients, surgical biopsy is most often contraindicated and pulmonary venoocclusive disease remains a diagnosis made at autopsy or transplantation. Clearly, a noninvasive pretreatment screening method would be helpful to identify patients at risk for worsening of clinical symptoms resulting from inappropriate medical treatment. Consequently, the purpose of our study was to evaluate pulmonary venoocclusive disease noninvasively with CT of the chest.
Materials and Methods
Patients
Our institutional review board did not require its approval or the patients' informed consent for this study. We reviewed cross-referenced records from 1996 to 2001 in the departments of radiology and pathology at our institution and identified 17 patients with pathologically confirmed pulmonary venoocclusive disease and a reference pretreatment CT scan obtained within 2 weeks after admission. One patient who underwent surgical biopsy was excluded because the diagnosis of pulmonary venoocclusive disease was probable but not certain. The pathologic hallmark of pulmonary venoocclusive disease was obstruction of the pulmonary veins and venules by intimal fibrosis, cellular proliferation, and muscularization (Fig. 1A). One patient with associated arterial plexiform lesions was also excluded from the study. Therefore, 15 patients (six men and nine women; mean age ± SD, 41.2 ± 11.7 years) constituted our study group. The diagnosis of pulmonary venoocclusive disease was established in all patients via either a postmortem (n = 6) or posttransplantation (n = 9) examination.
We reviewed the cross-referenced records of the same two departments to identify 15 consecutive patients with pathologically confirmed primary pulmonary hypertension (characterized by lesions of plexogenic arteriopathy without evidence of hemosiderosis or capillary and venous modifications [Fig. 1B]) and a reference pretreatment CT scan obtained within 2 weeks after admission. These 15 patients (four men and 11 women; mean age ± SD, 45.5 ± 17.6 years) constituted our reference group. The diagnosis of primary pulmonary hypertension was established in all patients via either a postmortem (n = 11) or posttransplantation (n = 4) examination.
Methods
The CT examination was performed within the first 2 weeks after admission (study group, 2.6 ± 2.7 days; reference group, 4.7 ± 4.6 days) before initiation of any vasodilator treatment and always included a thin-section CT sequence and helical CT angiography. CT scans were obtained using a HiSpeed scanner (General Electric Medical System) at end-inspiration in the patients in the supine position. Thin-section CT was performed with 1-mm section thickness at 10-mm intervals; reconstruction matrix, 512 × 512; high-spatial-frequency reconstruction algorithm; field of view, 28–34 cm; exposure, 1 sec; 130 kV; and 100 mAs, without injection of contrast medium. For helical CT angiography, data were acquired with a collimation of 3 mm and a pitch of 1.7, 180 mAs, 120 kV, and reconstruction of overlapping images at 2-mm intervals. Helical CT was initiated at the level of the aortic arch to the level of the inferior wall of the right ventricle, and scanning was completed during a single breath-hold. We injected 140 mL of contrast material ([iohexol] Omnipaque 300; Nycomed Ingenor) at a rate of 4.0–4.5 mL/sec and a delay of 15–20 sec. Scans were photographed with both soft-tissue (level, 30 H; width, 300 H) and lung (level, –600 H; width, 1,600 H) window settings.
CT scans were reviewed by three chest radiologists who were unaware of the pathologic diagnosis. Final decisions on the findings were reached by consensus.
Grading CT Scans
CT scans were assessed for the presence of different pathologic features (Table 1). For ground-glass opacities and septal lines, severity and zonal predominance were also taken into account. Severity was rated on a 4-point scale according to the lung parenchyma extension: Normal findings were coded as 0, no ground-glass opacities or septal lines present; abnormal findings involving less than one third of the lung were coded as 1, abnormal findings involving between one third and two thirds of the lung were coded as 2, and pathologic findings involving more than two thirds of the lungs were coded as 3.
| CT Finding | All Patients (n = 30) | Pulmonary Venoocclusive Disease (n = 15) | Primary Pulmonary Hypertension (n = 15) | p | Sensitivity (%) | Specificity (%) | |||
|---|---|---|---|---|---|---|---|---|---|
| No. | % | No. | % | No. | % | ||||
| Ground-glass opacities | 18 | 60 | 13 | 87 | 5 | 33 | 0.003a | 87 | 67 |
| Septal lines | 16 | 53 | 14 | 93 | 2 | 13 | < 0.0001a | 83 | 87 |
| Honeycombing | 1 | 3 | 1 | 7 | 0 | 0 | > 0.9b | ||
| Nonseptal lines | 2 | 7 | 2 | 13 | 0 | 0 | 0.48b | ||
| Nodules | 5 | 17 | 2 | 13 | 3 | 20 | > 0.9b | ||
| Emphysema | 1 | 3 | 1 | 7 | 0 | 0 | > 0.9b | ||
| Bronchiectasis | 2 | 7 | 2 | 13 | 0 | 0 | 0.48b | ||
| Pleural effusion | 6 | 20 | 4 | 27 | 2 | 13 | 0.65b | ||
| Pericardial effusion | 18 | 60 | 9 | 60 | 9 | 60 | NA | ||
| Lymph nodes | 12 | 40 | 12 | 80 | 0 | 0 | < 0.0001a | 80 | 100 |
| Cardiomegaly | 26 | 87 | 11 | 73 | 15 | 100 | 0.1b | ||
| rPA > 1a | 29 | 97 | 15 | 100 | 14 | 93 | > 0.9b | ||
| Enlarged pulmonary vein diameter | 0 | 0 | 0 | 0 | 0 | 0 | NA | ||
Note.—rPA = ratio of diameter of main pulmonary artery to that of the thoracic aorta, NA = not applicable.
a
Derived with chi-square test.
b
Derived with Fisher's exact test.
Zonal predominance was assessed as upper or lower, subpleural or central, or random. The upper lung zone was defined as the area above the level of the carina, and the lower lung zone was defined as the area below this level. The subpleural lung zone was defined as the outer third of the lung, and the central lung zone was defined as the inner two thirds of the lung. Scans were deemed to show random predominance when abnormal findings were a mixture of upper and lower predominance or a mixture of central and subpleural predominance.
Ground-glass opacity was defined as increased opacity of the lung parenchyma not sufficient to obscure pulmonary vessels. Patterns of ground-glass opacities were divided into two categories according to the lobular distribution [10]: centrilobular distribution corresponded to poorly defined nodular opacities ranging in diameter from a few millimeters to 1 cm, and panlobular distribution corresponded to geographic regions of lung attenuation with relatively well-defined borders that were either homogeneous (involving all the parenchyma to an equal degree) or heterogeneous (having various degrees of increased attenuation throughout the parenchyma) [11–13].
Septal lines corresponded to thickened interlobular septa (fine linear areas of attenuation or polygonal patterns of multiple polygonal lines), with smooth, irregular, or nodular borders. Mediastinal abnormalities evaluated included pericardial effusion, cardiomegaly, adenopathy (smallest diameter > 10 mm), enlargement of pulmonary arteries (ratio of the diameter of main pulmonary artery to that of the thoracic aorta, > 1 [14]), and pulmonary veins (subjective evaluation at the level of the left atrium).
Statistical Analysis
Statistical analysis was performed using StatView software (version 4.5, Abacus Concepts). Each CT finding was compared using the chi-square or the Fisher's exact test. The null hypothesis was rejected with a p value of less than 0.05. In such cases, sensitivity and specificity were also calculated.
Results
Overall CT findings (Table 1) and the incidence and characteristics of both ground-glass opacities (Table 2) and septal lines (Table 3) are summarized in respective tables.
| Characteristic | All Patients (n = 30) | Pulmonary Venoocclusive Disease (n = 15) | Primary Pulmonary Hypertension (n = 15) | p | Sensitivity (%) | Specificity (%) | |||
|---|---|---|---|---|---|---|---|---|---|
| No. | % | No. | % | No. | % | ||||
| Presence | 18 | 60 | 13 | 87 | 5 | 33 | 0.003 | 87 | 67 |
| Severitya | 0.02 | ||||||||
| 0 | 12 | 40 | 2 | 13 | 10 | 67 | |||
| 1 | 5 | 17 | 3 | 20 | 2 | 13 | |||
| 2 | 5 | 17 | 3 | 20 | 2 | 13 | |||
| 3 | 8 | 27 | 7 | 47 | 1 | 7 | |||
| Zonal predominance | |||||||||
| Craniocaudal | 0.18 | ||||||||
| Upper | 1 | 3 | 0 | 0 | 1 | 7 | |||
| Lower | 2 | 7 | 2 | 13 | 0 | 0 | |||
| Random | 15 | 50 | 11 | 73 | 4 | 27 | |||
| Peripheral | 0.52 | ||||||||
| Subpleural | 0 | 0 | 0 | 0 | 0 | 0 | |||
| Central | 0 | 0 | 1 | 7 | 0 | 0 | |||
| Random | 18 | 60 | 12 | 80 | 5 | 33 | |||
| Patterns | |||||||||
| Panlobular | 6 | 20b | 5 | 33b | 1 | 7 | 0.17c | ||
| Homogeneous | 3 | 10 | 2 | 13 | 1 | 7 | |||
| Heterogeneous | 3 | 10 | 3 | 20 | 0 | 0 | |||
| Centrilobular | 14 | 47b | 10 | 67b | 4 | 27 | 0.03d | 67 | 73 |
a
As graded on the following 4-point scale: 0 = not present, 1 = involving less than one third of the lung, 2 = involving between one third and two thirds of the lung, 3 = involving more than two thirds of the lung.
b
Two patients with pulmonary venoocclusive disease had both panlobular and centilobular patterns.
c
Derived with Fisher's exact test.
d
Derived with chi-square test.
| Characteristic | All Patients (n = 30) | Pulmonary Venoocclusive Disease (n = 15) | Primary Pulmonary Hypertension (n = 15) | pa | Sensitivity (%) | Specificity (%) | |||
|---|---|---|---|---|---|---|---|---|---|
| No. | % | No. | % | No. | % | ||||
| Presence | 16 | 53 | 14 | 93 | 2 | 13 | < 0.0001 | 93 | 87 |
| Severityb | 0.0002 | ||||||||
| 0 | 14 | 47 | 1 | 7 | 13 | 87 | |||
| 1 | 11 | 37 | 9 | 60 | 2 | 13 | |||
| 2 | 4 | 13 | 4 | 27 | 0 | 0 | |||
| 3 | 1 | 3 | 1 | 7 | 0 | 0 | |||
| Zonal predominance | |||||||||
| Craniocaudal | 0.71 | ||||||||
| Upper | 5 | 17 | 4 | 27 | 1 | 7 | |||
| Lower | 3 | 10 | 3 | 20 | 0 | 0 | |||
| Random | 8 | 27 | 7 | 47 | 1 | 7 | |||
| Peripheral | 0.70 | ||||||||
| Subpleural | 15 | 50 | 13 | 87 | 2 | 13 | |||
| Central | 0 | 0 | 0 | 0 | 0 | 0 | |||
| Random | 1 | 3 | 1 | 7 | 0 | 0 | |||
a
Derived with chi-square test.
b
As graded on the following 4-point scale: 0 = not present, 1 = involving less than one third of the lung, 2 = involving between one third and two thirds of the lung, 3 = involving more than two thirds of the lung.
Ground-Glass Opacities
The presence of ground-glass opacities was significantly more frequent in pulmonary venoocclusive disease than in primary pulmonary hypertension. The zonal predominance of these opacities was most often random in the two groups of patients (craniocaudal zonal predominance, p = 0.18; peripheral zonal predominance, p = 0.52). The pattern of ground-glass opacities was an important factor because a centrilobular pattern (Fig. 2) was a significantly more frequent finding in patients with pulmonary venoocclusive disease than was the panlobular pattern (Fig. 3).
Septal Lines
For septal lines, CT showed smooth thickened interlobular septa in 16 (53%) of the 30 patients in our study population (Fig. 4). Fourteen (93%) of the 15 patients with pulmonary venoocclusive disease had thickened interlobular septa, whereas two (13%) of the 15 patients with primary pulmonary hypertension had thickened interlobular septa. Thus, thickened interlobular septa were more frequent in pulmonary venoocclusive disease than in primary pulmonary hypertension. In both pulmonary venoocclusive disease and primary pulmonary hypertension, peripheral zonal predominance was preferentially subpleural, with no craniocaudal zonal predominance noted.
Other Abnormal Parenchymal Findings
CT showed well-defined nodules in five patients, nonseptal lines in two patients, honeycombing in one patient, bronchiectasis in two patients, and emphysema in one patient. None of the abnormal findings correlated with the presence of pulmonary venoocclusive disease (Fisher's exact test, p > 0.05).
Pleural Effusion
CT showed a pleural effusion in six patients (20%)—four (27%) of the 15 patients with pulmonary venoocclusive disease, and two (13%) of the 15 patients with primary pulmonary hypertension. These results were not statistically significant (Fisher's exact test, p = 0.65).
Mediastinal Findings
CT showed a pericardial effusion in 18 patients (60%), adenopathy (mean ± standard deviation, 15 ± 5 mm) in 12 patients (40%), a right-sided chamber dilatation in 26 patients (87%), and a ratio greater than 1 between the diameters of the main pulmonary artery and the thoracic aorta in 29 patients (97%). The size of the primary pulmonary veins was normal in all patients. Differences in CT findings for pulmonary venoocclusive disease and primary pulmonary hypertension are summarized in Table 1. Among the mediastinal findings, only adenopathy was strongly correlated with pulmonary venoocclusive disease (Fisher's exact test, p < 0.0001). Sensitivity and specificity were 80% and 100%, respectively.
Discussion
Primary pulmonary hypertension is an idiopathic pulmonary hypertension that affects the precapillary (arterial) pulmonary circulation. Prostacyclin (PGI2)—a potent vasodilator and inhibitor of platelet aggregation produced by vascular endothelium—reduces pulmonary vascular resistance when administered acutely to patients with primary pulmonary hypertension. Its continuous infusion improves hemodynamics, exercise tolerance, quality of life, and survival. In contrast, pulmonary venoocclusive disease is a disease that affects the postcapillary (venous) pulmonary circulation, and prostacyclin therapy can result in life-threatening pulmonary edema. Indeed, if the pulmonary arterioles become dilated while the resistance of the pulmonary veins remains fixed, an increase in transcapillary hydrostatic pressure may ensue and produce florid pulmonary edema [3–6, 15]. It is therefore essential for clinicians to distinguish pulmonary venoocclusive disease from primary pulmonary hypertension. Unfortunately, the clinical presentation of pulmonary venoocclusive disease is similar to the presentation of other forms of pulmonary hypertension, mimicking primary pulmonary hypertension. So, the aim of our comparative study was to determine whether CT could be used to distinguish between these two entities. To our knowledge, previous studies concerning CT in pulmonary venoocclusive disease have only described CT findings without any comparison with the CT findings in primary pulmonary hypertension.
Our results support those in the literature [2, 7, 16]: ground-glass opacities and septal lines are highly suggestive of pulmonary venoocclusive disease. The pattern of ground-glass opacities varies from a minimal centrilobular patchy abnormality to an extensive diffuse inhomogeneous panlobular appearance [17–19]. Rare cases of an homogeneous panlobular pattern have been described [11, 20]. In our study, only the centrilobular pattern correlated with pulmonary venoocclusive disease (p = 0.02), with a specificity of 73%. This relatively poor specificity of centrilobular nodules could be explained by the presence of cholesterol granulomas in primary pulmonary hypertension. According to Nolan et al. [21], these granulomas occur in as many as 25% of patients with primary pulmonary hypertension, but these nodules are solitary with no septal lines or adenopathy. In pulmonary venoocclusive disease, centrilobular opacities should correspond to the first stage of the disease. Later, if these patchy opacities involve large continuous areas, one would expect to see inhomogeneous panlobular ground-glass opacities.
The panlobular pattern was unusual in our study and was not statistically significant, probably because of an insufficient number of patients. Nevertheless, it seemed to be more frequent in pulmonary venoocclusive disease, particularly when the pattern was heterogeneous. In our experience, a homogeneous mosaic pattern of ground-glass opacities is suggestive of chronic thromboembolic disease, and a postembolic secondary pulmonary hypertension should be proposed as differential diagnosis.
Enlargement of lymph nodes in pulmonary venoocclusive disease has been described in the literature as less frequent than we found in our study [2, 8]. This discordance could be explained by the CT technique and the small size of our adenopathies (15 ± 5 mm). All our patients underwent helical CT angiography before thin-section imaging, a protocol contrary to those of the previous studies. Unless contrast medium is injected and thin-section CT (1-mm section thickness at 10-mm intervals) is performed, a small adenopathic lesion can be missed. The presence of adenopathy in a patient with pulmonary hypertension is an important finding. Adenopathy is unusual in primary pulmonary hypertension [2, 7, 8, 19]. Apart from its appearance in pulmonary venoocclusive disease, enlargement of lymph nodes has previously been described only as a finding in pulmonary hypertension due to chronic thromboembolic diseases [22] or left-sided heart failure [23]. In the absence of findings suggestive of the two latter diseases, adenopathy is highly predictive of pulmonary venoocclusive disease, with a specificity of 100%. Nevertheless, because of the relatively low sensitivity (80%), the absence of adenopathy does not permit pulmonary venoocclusive disease to be excluded from the differential diagnosis.
Contrary to the findings of other studies, our results concerning pleural effusion showed no statistical significance (p = 0.65), although pleural effusion was slightly more frequent in pulmonary venoocclusive disease. Pericardial effusion was a frequent finding in both pulmonary venoocclusive disease and primary pulmonary hypertension. This frequency could be explained by the high prevalence of pericardial effusion in patients with severe pulmonary hypertension [24, 25].
This study has some limitations. First, the number of patients was small because the occurrence of pulmonary venoocclusive disease is rare. However, approximately only 150 cases have been reported in the literature [2], and to our knowledge, our series of 15 patients with a pathologically proven diagnosis of pulmonary venoocclusive disease represents the largest to date. The lack of follow-up is another limitation because primary pulmonary hypertension can have a radiologic presentation that mimics pulmonary venoocclusive disease after several years of treatment [26]. Nevertheless, this distinction is particularly important before the initiation of medical treatment with prostacyclin, which is potentially fatal in patients with pulmonary venoocclusive disease. Finally, in all 30 patients, we had pathologic proof of the diagnosis of pulmonary venoocclusive disease or primary pulmonary hypertension, but unfortunately a comparison between each CT scan and pathologic findings was not feasible because the CT and pathologic examinations were not performed at the same time.
Our conclusion is that in patients with pulmonary hypertension—after exclusion of secondary causes such as left-sided heart failure or chronic pulmonary thromboembolic disease—the presence of ground-glass opacities with a centrilobular pattern (poorly defined centrilobular opacities), septal thickening, and adenopathy on the initial pretreatment CT scan should raise suspicions of pulmonary venoocclusive disease. Ground-glass opacities and septal lines have a high sensitivity for pulmonary venoocclusive disease, and the disease is unlikely in absence of these findings. The specificity of adenopathy is also high; if adenopathy is present, pulmonary venoocclusive disease is likely to be the correct diagnosis.
Footnote
Address correspondence to A. Resten ([email protected]).
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Submitted: October 9, 2003
Accepted: January 21, 2004
First published: November 23, 2012
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