|Year : 2010 | Volume
| Issue : 1 | Page : 26-32
Computed tomographic pulmonary angiography: Utility in acute pulmonary embolism in providing additional information and making alternative clinical diagnosis
Kushaljit Singh Sodhi1, Madhu Gulati1, Ritesh Aggarwal2, Naveen Kalra1, BR Mittal3, SK Jindal2, N Khandelwal1
1 Department of Radiodiagnosis, PGIMER, Chandigarh, India
2 Department of Pulmonary Medicine, PGIMER, Chandigarh, India
3 Department of Nuclear Medicine, PGIMER, Chandigarh, India
|Date of Web Publication||31-Jan-2012|
Kushaljit Singh Sodhi
Department of Radiodiagnosis, PGIMER, Chandigarh - 160 012
Objective: To evaluate the role of computed tomographic (CT) pulmonary angiography (CT-PA) in detecting additional information that may help in making an alternative clinical diagnosis in patients referred to CT for a suspected acute pulmonary embolism (PE). Materials and Methods: 50 patients (34 males, 16 females) in the age group of 18-72 years (mean 42.3 years), having high clinical suspicion of PE, underwent CTPA over a 2 year period. Chest x-ray, arterial blood gas (ABG) analysis, echocardiography were done in all patients. All patients underwent at least one other imaging examination besides CTPA: ventilation perfusion scan, Doppler ultrasound or compression ultrasound (for DVT). All patients were followed for 3 months after completion of the diagnostic work up at baseline. The final diagnosis was achieved by a combination of clinical, imaging, and laboratory analysis, after adequate imaging, laboratory tests, and follow up. Result: CTPA helped correctly identify 29 of 30 patients with PE. In the remaining 20 patients (with no evidence of PE), CT-PA provided additional information (that suggested or confirmed alternate clinical diagnosis) in 15 patients (75%): pleural effusion (n=8), mediastinal or hilar lymphadenopathy (6), pneumonia/airspace consolidation (5), atelectasis/collapse (2), aspergilloma (1), malignancy (1), and others (2). Conclusion: CT-PA is highly specific and sensitive for diagnosis of PE. In addition, in a majority of patients who do not have PE, it also provides important ancillary additional information and helps in making an alternative clinical diagnosis.
Keywords: Pulmonary embolism and diagnosis, reproducibility of results or sensitivity and specificity, tomography, X-ray computed
|How to cite this article:|
Sodhi KS, Gulati M, Aggarwal R, Kalra N, Mittal B R, Jindal S K, Khandelwal N. Computed tomographic pulmonary angiography: Utility in acute pulmonary embolism in providing additional information and making alternative clinical diagnosis. Indian J Med Sci 2010;64:26-32
|How to cite this URL:|
Sodhi KS, Gulati M, Aggarwal R, Kalra N, Mittal B R, Jindal S K, Khandelwal N. Computed tomographic pulmonary angiography: Utility in acute pulmonary embolism in providing additional information and making alternative clinical diagnosis. Indian J Med Sci [serial online] 2010 [cited 2013 Jun 18];64:26-32. Available from: http://www.indianjmedsci.org/text.asp?2010/64/1/26/92484
| ¤ Introduction|| |
Pulmonary embolism (PE) is associated with considerable morbidity and mortality and has the potential to masquerade as a variety of other common disorders. , Nearly 10% of the patients with PE do not survive the initial embolic event. ,
- The overall mortality rate for patients with untreated PE is reported to be 30%. , Although recent articles  do indicate that deaths from PE have decreased by 30%. This change is likely due to a combination of factors including changes in diagnostic patterns and decreased incidence of PE.
- Spiral CT angiography is increasingly being used as the first-line imaging test in patients clinically suspected of PE. ,,,,, CT pulmonary angiography is a safe, noninvasive, quick test, that can be easily performed in an emergency setting to directly identify the presence and extent of PE. Several recent studies have shown overall sensitivity ranging from 64% to 100% and specificities from 89% to 100%. ,, With the advent of multi-detector computed tomography (MDCT), there is further incremental improvement, in detection of segmental and subseqmental emboli. 
- A potential advantage of spiral CT is its capability to provide concurrently high quality images of mediastinum, lung parenchyma, and chest wall, and thus provides important additional diagnostic information (that may explain the patients signs and symptoms) in patients, proved not to have PE.
- It is highly relevant to the clinician as approximately 60-70% of patients, with clinically suspected PE, are proved not to have PE after a series of diagnostic investigations. ,,,
- Ventilation perfusion (V-P) scintigraphy and pulmonary angiography have also been used in the diagnostic algorithm for acute PE; however, these tests do not provide adequate additional information about other anatomical studies of the chest.
This study was not designed to compare the diagnostic accuracy of CT with V-P scans or other imaging modalities in acute PE but the aim of this study was to evaluate the role of CT pulmonary angiography (CT-PA) in detecting additional information that may help in making an alternative diagnosis, in patients referred to CT for a suspected acute PE.
| ¤ Materials and Methods|| |
Consecutive contrast-enhanced CT pulmonary angiography scans of 50 patients (34 men, 16 women, age range 18-72 years mean age 42.3 years) with high clinical suspicion of PE were retrospectively reviewed. These patients were referred to the imaging department of an (tertiary referral level) academic medical center, over a 2-year period. The study included all patients who showed high suspicion of having PE based on clinical parameters:
- Hemodynamic compromise (systolic BP < 90 mmHg)
- Right ventricular dysfunction (on echocardiography)
- Hypoxemia (PaO 2 < 60 mmHg)
- Sudden onset of dyspnea/chest pain/unexplained deterioration of symptoms
- One or more risk factors for venous thrombo-embolism.
Informed consent was obtained from all patients, and ethical approval was obtained from departmental review board. All imaging studies were completed within 48 h.
Breathlessness (dyspnea) was the most common presenting complaint, followed by cough, chest pain, and hemoptysis.
| ¤ CT Protocol|| |
Spiral CT scan used in this study was a light speed 4 row multi-detector CT (Qxi, GE Medical System, Milwaukee, Wisconsin). Contrast-enhanced evaluation of the central and segmental pulmonary arteries was performed from the level of diaphragm to aortic arch, in a caudo-cranial direction. Scanning was started, using smart prep protocol (GE) by placing ROI (region of Interest) cursor in the main pulmonary artery.
Scanning parameters included a collimation thickness of 3mm, a pitch of 1.5-2.0, 120 kvp, 300 mA. Images were reconstructed at 1.5-mm interval using the standard reconstruction algorithm and a field of view appropriate to the patient size.
The contrast protocol was standardized in all patients. 100 ml of 30% contrast agent (Ultravist 300, Schering, Berlin, Germany) was injected with an power injector through an 18-20 gauge venous line in anticubital fossa or through central venous catheter, at a flow rate of 4 ml/ s using an timing bolus (smart prep technique). CT scans which were of non-diagnostic quality and inconclusive for PE and lung abnormalities (due to poor contrast opacification/motion degradation) were excluded from this study.
All CT examinations were read and interpreted by two radiologists, independently on a viewing work station using three window and level settings:
- Mediastinal (window width 450 HU, window level 35HU)
- Lung parenchyma (window width 1500 HU, window level -600 HU)
- Pulmonary vascular (window width 250 HU, window level 40 HU)
Observers were allowed to change these settings. Overlapping images (reconstructed at 5 mm) were also printed on hard copy film at two standard (mediastinal and lung parenchymal) settings. Evaluation of central, segmental, and subsegmental pulmonary arteries was first done to detect PE. Subsequently, all other abnormalities in the mediastinum, chest wall, lung parenchyma, soft tissues, pleural/pericardial, cardiovascular system were also looked for and recorded.
All clinical data was available at the time of interpretation of images. At the end of the entire diagnostic work up, all available imaging, laboratory analysis, and clinical information was used by the radiologists to provide a possible alternative diagnosis in cases with excluded PE on CT - PA.
Other imaging tests for PE
V-P scintigraphy and Doppler ultrasound for deep venous thrombosis were performed at the clinician's discretion. However chest x-ray, arterial blood gas analysis (ABG), compression sonography, and echocardiography (Echo) were done in all patients.
| ¤ Results|| |
PE was diagnosed in 30 patients based on a combination of clinical and imaging analysis. CT pulmonary angiography (CT-PA) was positive (true positive) in 29/30 patients. Out of the 29 patients who showed evidence of pulmonary thromboembolism on CT-PA, PE involved bilateral pulmonary arteries in 20, unilateral pulmonary arteries in 7, while segmental involvement was seen in 2 patients.
In the remaining 20 patients, without PE, the final diagnosis was achieved by a combination of clinical, imaging, and laboratory analysis, after adequate imaging, laboratory tests and follow up. Five patients out of the 20 patients without PE had normal spiral CT scans of the chest. In 15 patients without PE, CT-PA provided additional diagnostic information that suggested an alternate diagnosis [Table 1], [Figure 1], [Figure 2] and [Figure 3] which was pleural effusion (n=8), mediastinal/hilar lymphadenopathy (n=6), pneumonia/air space consolidation (n=5), atelectasis/collapse (n=2), lung mass with metastasis (n=1), aspergilloma (n=1), and others (n=2). Others included one patient of pulmonary fibrosis (1) and emphysema (1). In none of these 20 patients (who had negative findings of PE) was an alternative diagnosis made/suggested by V-P scintigraphy/echocardiography/other tests.
|Figure 1: Contrast-enhanced spiral CT at the level of aortic arch shows airspace consolidation with breakdown in the right upper lobe. Diagnosis: Necrotizing pneumonia|
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|Figure 2: CECT chest reveals a large left upper lobe mass with pulmonary metastasis|
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|Figure 3: CECT chest reveals calcified and necrotic (a) mediastinal and (b) left hilar lymphadenopathy (arrows). This suggested a diagnosis of tuberculosis|
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|Table 1: Additional information on MDCT - 15 patients (suggested/confirmed alternate clinical diagnosis)|
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All patients were followed for 3 months after completion of the diagnostic work up at baseline . All patients with negative CTPA results which were followed up did not reveal any new/further evidence to suggest PE. During follow up, all patients received routine clinical care from their physicians aimed at treating the alternative diagnosis and to look for any signs or symptoms suggesting PE or DVT.
| ¤ Discussion|| |
The diagnostic accuracy of CT-PA in PE in this study is comparable to that of previous studies. In 15 (75%) out of the 20 patients without PE, spiral CT (CT-PA) added diagnostic information that suggested an alternate diagnosis. This additional diagnostic information was not provided by other currently used screening modalities for P.E. i.e., V-P scintigraphy, Doppler USG, and echocardiography. This represents a diagnostic advantage for spiral CT in these patients. Similar results were found by Kim et al  who performed the first such study that has reported on alternative findings and diagnosis in patients with clinically suspected PE. They found additional finding on spiral CT in 67% of patients, without PE, (on spiral CT). There have been very few similar studies , that have highlighted utility of spiral CT in providing an alternative diagnosis in patients of clinically suspected PE. Van Strijen MJL et al,  performed multi-center study in clinically suspected PE patients and found that helical CT allows a reliable alternative diagnosis to be made in 25.4% of patients.
It is important to note that the presence of pathologic change suggesting an alternative diagnosis cannot and should not be used as the sole criteria to exclude PE. , Previous studies  have shown that parenchymal abnormalities can be found in 86% of patients with PE and 88% patients without PE. Therefore, the first step in work up of such patients should be to exclude PE by carefully evaluating central segmental and subsegmental vessels. 
In our study, CT-PA proved to very accurate in diagnosing PE. In conjunction with these 29 patients, in whom PE was correctly diagnosed at spiral CT, useful information was obtained in 15 other patients. In this particular series, the most common diagnosis in patients without PE and with an abnormal chest CT included: pleural effusion (n=8), mediastinal/hilar lymphadenopathy (n=6), Pneumonia (n=5), atelectasis (n=2), lung mass (n=1), aspergilloma (n=1), and others (n=2). Five patients had completely normal spiral CT chest. For the purpose of this study, a normal MDCT-PA was classified as not providing any additional diagnostic information.
Multi-detector CT pulmonary angiography is becoming established as the first line imaging test in patients suspected of having PE, as it gives information about both vascular and non-vascular thoracic structures at the same time.
The study has several limitations. Firstly, CT- PA (Spiral CT) was used as the standard of reference for the presence or the absence of PE. (Although final diagnosis was reached by a combination of clinical, imaging and laboratory findings and at least one more imaging modality apart from CT scan). Since pulmonary angiograms were not obtained, the diagnosis of PE is biased towards patients with larger/segmental emboli. This bias is similar to that of a previous study (Kim 1), in which spiral CT was used. The high degree of accuracy of spiral CT with ever increasing sensitivity and specificity (>90%) in detecting emboli to the level of segmental or pulmonary arteries is currently accepted.  The prevalence of small subsegmental emboli is still the subject of debate and their clinical significance when detected remains doubtful. 
A recent study  has found that increased visualization of smaller subsegmental, more peripheral arteries afforded by multi-slice technology does not affect clinical outcome.
Further limitation of this study is that it was not possible to obtain a standard reference test for every suggested alternative diagnosis. This was overcome in author's view by performing routine follow up in all patients to see for any changes in alternative diagnosis determined at the time of CT scan and response to medical management.
One reason of high true positives in our study could be our selection basis. We had already excluded CT scans which were of non-diagnostic quality and inconclusive for PE and lung abnormalities. Secondly, only patients with a very high clinical suspicion for PE were enrolled in this study.
Another possible limitation perhaps could be the short follow-up time interval of 3 months, which was however considered adequate by the authors.
This study was not designed to compare the diagnostic accuracy of CT with V-P scans or other imaging modalities in acute PE but to evaluate the role of spiral CT (CT-PA) in providing additional diagnostic information in patients suspected of having PE but with no PE.
In conclusion, CT pulmonary angiography has good sensitivity and specificity for diagnosis of PE. It also provides important additional information to make an alternative clinical diagnosis in patients suspected of having acute PE but patients who do not have PE. This additional information is not possible with other PE screening modalities.
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[Figure 1], [Figure 2], [Figure 3]