Acute pulmonary embolism: ancillary findings at spiral CT

Pulmonary infarction: spectrum of findings on multidetector helical CT

OBJECTIVE

Despite the dual blood supply to the lung, acute pulmonary embolism (PE) can lead to a spectrum of ischemic injury to the lung resulting in infarction and hemorrhage. In this series we systematically describe the spectrum of CT findings and clinical correlates of pulmonary infarction in patients with PE.

METHODS

We retrospectively identified 24 consecutive adults with pulmonary infarction on multidetector CT between July 2002 and March 2004. There were 13 women and 11 men, with a mean age of 59 years. The cases were identified by review of 74 consecutive CTs demonstrating PE. Each CT was evaluated by 2 of 3 reviewers in consensus for presence and characteristics of peripheral parenchymal opacities and extent of PE. Peripheral opacities were evaluated for degree of enhancement, internal air lucencies, and contour. The presence of adjacent vessels and linear strands were noted. At the end of interpreting each case, the reviewers determined whether or not an infarct was present based on the constellation of previously described imaging features. The extent of pulmonary vascular obstruction was graded using the CT clot burden scoring system. Each chart was reviewed for predisposing factors for PE and infarction, presenting clinical symptoms/signs, and co-existing pulmonary or cardiac conditions.

RESULTS

Thirty-two percent (24/74) of patients with PE had pulmonary infarction. Thirty-three percent (8/24) of patients had more than 1 infarct. Seventy-three percent (27/37) of infarcts were in the lower lobes. The CT findings of pulmonary infarction included: focal decrease in parenchymal enhancement in 95% (35/37), broad pleural base in 65% (24/37), truncated apex in 57% (21/37), convex border in 46% (17/37), internal air lucencies in 32% (12/37), linear stranding from the apex toward the hilum in 24% (9/37), and a thickened vessel leading to the apex of the infarct in 14% (5/37). There was a trend toward a higher mean clot burden (12.3 vs. 10.5) between the patients with PE with and without infarction. Ninety-six percent (23/24) of patients with pulmonary infarction had predisposing factors for infarction, including PE involving more than 1 lobe (n = 21), malignancy (n = 5), and heart failure (n = 3). Pleuritic chest pain was significantly more frequent in patients with infarction (P = 0.0064).

CONCLUSION

Pulmonary infarction occurred in nearly 1/3 of patients with PE in this series. The infarcts were peripheral parenchymal opacities characterized by a distinctive complex of findings on CT reflecting ischemic injury in the setting of a dual blood supply to the lung. Pleuritic chest pain was significantly associated with infarction.

Quantification of Thin-Section CT Lung Attenuation in Acute Pulmonary Embolism: Correlations with Arterial Blood Gas Levels and CT Angiography

OBJECTIVE

The purposes of this study were to investigate the frequency histogram of lung attenuation on CT angiography (CTA) in patients with and without acute pulmonary embolism (PE) and to evaluate the relation of the frequency histogram of lung attenuation and hypoxemia.

MATERIALS AND METHODS

Twenty-six patients with PE and 11 patients without PE who underwent CTA were evaluated with frequency histograms. We obtained quantitative parameters such as mean lung attenuation, median lung attenuation, SD, skewness, kurtosis, and the proportion of lung attenuation except for the median +/- 50 H (P +/- 50 H). Lung attenuation was also assessed visually and scored. The relationship between those histogram parameters, or visual score, and Pa(O2) was evaluated. CTA scores for evaluation of the degree of pulmonary artery obstruction were obtained, and the relation with Pa(O2) was assessed.

RESULTS

No significant differences were found in mean lung attenuation and median lung attenuation between patients with and without PE. Meanwhile, SD, skewness, kurtosis, and P +/- 50 H were significantly different between patients with and without PE (p = 0.0003, 0.0071, 0.0047, and 0.0028, respectively) and significantly correlated with Pa(O2) (r = -0.770, 0.797, 0.786, -0.871, respectively). Significant differences were found in visual scores between patients with and without PE (p < 0.0001). There were significant but relatively low correlations between CTA score and arterial blood gas levels (r = -0.442, p = 0.03).

CONCLUSION

In patients with acute PE, heterogeneity in lung attenuation is more prominent than in patients without PE.

Multidetector row CT pulmonary angiography and indirect venography for the diagnosis of venous thromboembolic disease in intensive care unit patients

RATIONALE AND OBJECTIVES

To determine the diagnostic quality, performance characteristics and interreader reliability of computed tomography pulmonary angiography (CTPA) and venography (CTV) in intensive care unit (ICU) patients with suspected venous thromboembolism (VTE).

MATERIALS AND METHODS

A total of 100 consecutive ICU patient CT examinations performed for clinically suspected VTE on a four-row CT scanner were reviewed. Three readers rated the diagnostic quality of each CTPA and CTV examination as excellent, acceptable, or nondiagnostic. Readers scored the overall determination for pulmonary embolism (PE) and deep venous thrombosis (DVT) using a 5-point scale, and scored the determination for PE by anatomic level. Receiver operator characteristic (ROC) analysis was performed for each reader and the original clinical report, using consensus interpretation as the reference standard. Interobserver variability for PE and DVT was determined using kappa analysis, and was stratified by examination quality.

RESULTS

A total of 25% of CTPA examinations were nondiagnostic, most commonly because of motion artifact and poor contrast opacification. A total of 24% of CTV examinations were nondiagnostic, most commonly because of poor contrast opacification and metallic hardware. Using receiver operating characteristic analysis, the areas under the curve (Az) for PE diagnosis were 0.875, 0.923, 0.888, and 0.674 for the three readers and clinical reading, respectively, and for DVT diagnosis were 0.842, 0.859, 0.952 and 0.669. Interobserver agreement for detection of PE was moderate at the supralobar level (kappa = 0.55), very good at the lobar level (kappa = 0.69), and moderate for segmental (kappa = 0.54) and subsegmental arteries (kappa = 0.44). Overall reader agreement was good for excellent/good quality CTPA examinations (kappa = 0.52-0.56), and poor when examination quality was poor (kappa = 0.06).

CONCLUSIONS

CTPA and CTV are sufficiently accurate and reliable techniques for evaluating VTE in ICU patients, particularly in light of patient complexity.

Suspected and incidental pulmonary embolism on multidetector-row CT: Analysis of technical and morphological factors influencing the diagnosis in a cross-sectional cancer centre patient cohort

AIM

To assess technical and computed tomography (CT) predictors of true-positive (TP) and false-negative (FN) radiological diagnoses in a retrospective patient cohort with pulmonary embolism (PE) in the setting of a cancer centre.

MATERIALS AND METHODS

Two thousand, four hundred and twelve consecutive chest multidetector-row CT images from 1869 patients were reviewed for presence of PE. CT protocols and TP and FN radiological reports were determined and the clinical files reviewed for suspicion of PE. The severity of PE was assessed by an arterial obstruction index. Ancillary pulmonary findings were scored qualitatively and on a lobar basis. Statistical tests included analysis of variance and univariate and multivariate logistic regressions.

RESULTS

Ninety-one out of a total of 111 PE-positive images were included. Thirty-five patients had clinically suspected PE; 56 were not suspected of having PE. Forty-eight patients had TP diagnoses; 43 (39 of whom were not suspected of having PE) had FN radiological diagnoses. FN diagnoses were most frequent in oesophageal (17/19; 89.5%) and standard chest CT (19/35; 54.3%). Pulmonary CT angiography was associated with TP diagnosis (p<0.0001), whereas oesophageal CT was associated with FN diagnosis (p=0.001). Artefacts and arterial attenuation did not influence PE detection (p=0.017 and 0.066 for artefacts and arterial attenuation, respectively). However, the arterial obstruction index strongly predicted PE diagnosis (p=0.001). This was confirmed on multivariate analysis (p=0.041, 0.027 and 0.020 for pulmonary CT angiography, oesophageal protocols and arterial obstruction index, respectively). When stratified for clinically unsuspected cases, the arterial obstruction index remained the only predictor of PE diagnosis (p=0.009).

CONCLUSION

Predictors of PE diagnosis were PE severity and technical factors; the latter were linked to clinical suspicion of PE. Arterial enhancement appears unlikely to contribute to missed diagnoses, if judged adequate for diagnosis of PE, and ancillary chest findings are unlikely to improve embolus detection.

Comprehensive assessment of lung CT attenuation alteration at perfusion defects of acute pulmonary thromboembolism with breath-hold SPECT-CT fusion images

Regional computed tomography attenuation (CTA) alteration at perfusion defects in acute pulmonary thromboembolism (PTE) was comprehensively assessed using deep-inspiratory breath-hold SPECT-CT fusion images. Subjects were 14 acute and 9 chronic PTE patients and 13 control subjects. Regional perfusion, CTA, and intravascular clots were correlated on deep-inspiratory breath-hold SPECT-unenhanced/angiographic CT fusion images. Fusion images visualized hypo-CTA in 57% of the acute PTE patients, which preferentially occurred at extensively and severely decreased perfusion areas caused by central clots. CTA at 35 defects of acute PTE was significantly decreased compared with that of normal lungs (P<0.001), but the degree was less compared with chronic PTE (P<0.0001). Fusion images also revealed variable relationships of clots and regional perfusion/CTA in the distal lungs of each central clot. Fusion images provide important information about the actual effects of intravascular clots on peripheral perfusion/CTA and indicate that lung CTA can be decreased at perfusion defects in acute PTE.

Thoracic ultrasound for diagnosing pulmonary embolism: a prospective multicenter study of 352 patients

BACKGROUND

Pulmonary embolism (PE) continues to be a major challenge in terms of diagnosis, as evidenced by the fact that many patients die undiagnosed and/or untreated. The aim of this multicenter study was to determine the accuracy of thorax ultrasound (TUS) in the diagnosis of PE (TUSPE).

METHODS

From January 2002 through September 2003, 352 patients with suspected PE were examined in seven clinics. The patients were investigated prospectively by TUS according to the following criteria: (1) PE confirmed: two or more typical triangular or rounded pleural-based lesions; (2) PE probable: one typical lesion with pleural effusion; (3) PE possible: small (< 5 mm) subpleural lesions or a single pleural effusion alone; or (4) normal TUS findings. In all cases, CT pulmonary angiography (CTPA) was used as the reference method. In the event of discrepant findings, a combination of duplex sonography of the leg veins, echocardiography, ventilation/perfusion scintigraphy, and a quantitative enzyme-linked immunosorbent assay or latex d-dimer, or a biopsy/autopsy was performed.

FINDINGS

PE was diagnosed in 194 patients. On TUS, 144 patients had a total of 333 subpleural lesions (mean, 2.3 lesions per patient) averaging 15.5 x 12.4 mm in size. Additionally, a narrow pleural effusion was found in 49% of the patients. TUS yielded the following results under application of the strict criteria 1 and 2: PE true-positive, n = 144; PE false-positive, n = 8; PE true-negative, n = 150; and PE false-negative, n = 50. The sensitivity was 74%, specificity was 95%, positive predictive value was 95%, negative predictive was value 75%, and accuracy was 84%, at a prevalence of 55%. The sensitivity in patients with criterion 1 was 43% and a specificity of 99%.

INTERPRETATION

TUS is a noninvasive method to diagnose peripheral PE. In the absence of CTPA, TUS is a suitable tool to demonstrate a PE at the bedside and in the emergency setting.

Helical computed tomography and alternative diagnosis in patients with excluded pulmonary embolism

OBJECTIVE

A clinical diagnosis of pulmonary embolism (PE) is confirmed objectively in 20-30% of patients. Helical computed tomography (CT) can allow an alternative diagnosis to be made. The frequency and validity of alternative diagnoses on helical CT in consecutive patients presenting with clinically suspected PE was assessed.

PATIENTS AND METHODS

In all 512 prospectively analyzed patients helical CT scan was performed, and apart from presence or absence of PE, pathologic changes in lung parenchyma, mediastinum, cardiovascular system, pleura and skeleton were recorded. When possible an alternative diagnosis was given and compared with the final diagnosis after 3 months follow-up.

RESULTS

In 130 patients (25.4%) PE was excluded and an alternative diagnosis considered likely. In 123 of the 130 patients (94.6%) this diagnosis was unchanged at 3 months follow-up. The diagnoses included pneumonia (n = 67), malignancy (n = 22), pleural fluid (n = 10), cardiac failure (n = 10), COPD (n = 6) and a variety of other causes (n = 15). The diagnosis changed at follow-up in seven patients (5.4%). An initial diagnosis of pneumonia changed to malignancy in two patients and to pleuritis and cardiac failure in one patient each. In two other patients malignancy and chronic obstructive pulmonary disease (COPD) were ruled out and the diagnosis changed to pneumonia. In one patient the final diagnosis remained unknown after an initial suspicion of malignancy.

CONCLUSION

In clinically suspected PE helical CT allows a reliable alternative diagnosis to be made in 25.4% of patients. This feature is an unique advantage in comparison with other diagnostic tests and supports the decision of taking helical CT as first line test in suspected PE.

CT angiography of pulmonary embolism: diagnostic criteria and causes of misdiagnosis

Computed tomographic (CT) pulmonary angiography is becoming the standard of care at many institutions for the evaluation of patients with suspected pulmonary embolism. This pathologic condition, whether acute or chronic, causes both partial and complete intraluminal filling defects, which should have a sharp interface with intravascular contrast material. In acute pulmonary embolism that manifests as complete arterial occlusion, the affected artery may be enlarged. Partial filling defects due to acute pulmonary embolism are often centrally located, but when eccentrically located they form acute angles with the vessel wall. Chronic pulmonary embolism can manifest as complete occlusive disease in vessels that are smaller than adjacent patent vessels. Other CT pulmonary angiographic findings in chronic pulmonary embolism include evidence of recanalization, webs or flaps, and partial filling defects that form obtuse angles with the vessel wall. Factors that cause misdiagnosis of pulmonary embolism may be patient related, technical, anatomic, or pathologic. The radiologist needs to determine the quality of a CT pulmonary angiographic study and whether pulmonary embolism is present. If the quality of the study is poor, the radiologist should identify which pulmonary arteries have been rendered indeterminate and whether additional imaging is necessary.

CT Scan Findings in Chronic Thromboembolic Pulmonary Hypertension

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.

Vascular Diseases of the Thorax: Evaluation with Multidetector CT

The list of vascular diseases in the thorax has been narrowed to three, which are considered essential information for radiologists interpreting CT scans of the thorax: (1) aortic dissection and its variants, intramural hematoma and penetrating atherosclerotic ulcer; (2) acute pulmonary embolism; and (3) coronary artery disease. The spatial resolution of multidetector CT is such that CT has become the imaging modality of choice for aortic dissection and pulmonary embolism. This move away from angiography has transpired over the last decade; perhaps the next decade will see the same occur for evaluation of coronary artery disease.

Multislice computed tomography perfusion imaging for visualization of acute pulmonary embolism: animal experience

The purpose of our animal study was to evaluate a new computed tomography (CT) subtraction technique for visualization of perfusion defects within the lung parenchyma in subsegmental pulmonary embolism (PE). Seven healthy pigs were entered into a prospective trial. Acute PE was artificially induced by fresh clot material prior to the CT scans. Within a single breath-hold, whole thorax CT scans were performed with a 16-slice multidetector-row CT scanner (SOMATOM Sensation 16; Siemens, Forchheim, Germany) before and after intravenous application of 80 ml of contrast medium with a flow rate of 4 ml/s, followed by a saline chaser. The scan parameters were 120 kV and 100 mAs(eff), using a thin collimation of 16x0.75 mm and a table speed/rotation of 15-18 mm (pitch, 1.25-1.5; rotation time, 0.5 s). Axial source images were reconstructed with an effective slice thickness of 1 mm (overlap, 30%). A new automatic subtraction technique was used. After 3D segmentation of the lungs in the plain and contrast-enhanced series, threshold-based extraction of major airways and vascular structures in the contrast images was performed. This segmentation was repeated in the plain CT images segmenting the same number of vessels and airways as in the contrast images. Both scans were registered onto each other using nonrigid registration. After registration both image sets were filtered in a nonlinear fashion excluding segmented airways and vessels. After subtracting the plain CT data from the contrast data the resulting enhancement images were color-encoded and overlaid onto the contrast-enhanced CT angiography (CTA) images. This color-encoded combined display of parenchymal enhancement of the lungs was evaluated interactively on a workstation (Leonardo, Siemens) in axial, coronal and sagittal plane orientations. Axial contrast-enhanced CTA images were rated first, followed by an analysis of the combination images. Finally, CTA images were reread focusing on areas with perfusion deficits indicating PE on the color-coded enhancement display. Subtraction was feasible for all seven studies. In one animal, opacification of the pulmonary arteries was suboptimal owing to heart insufficiency. In the remaining six pigs, a total of 37 perfusion defects were clearly assessable downstream of occluded subsegmental arteries, showing lower or missing enhancement compared with normally perfused lung parenchyma. Indeterminate findings from CTA showed typical PE perfusion defects in four out of six cases on CT subtraction. Additionally, 22 peripheral triangular-shaped enhancement defects were delineated. Nine of these findings were reclassified as definitely being caused by PE on second reading of the CTA data sets. Our initial results have shown that this new subtraction technique for perfusion imaging of PE is feasible, using routine contrast delivery. Dedicated examination protocols are mandatory for adequate opacification of the pulmonary arteries and for optimization of data sets for subsequent subtraction. Perfusion imaging allows a comprehensive assessment of morphology and function, providing more accurate information on acute PE.

Ancillary lung parenchymal findings at spiral CT scanning in pulmonary embolism. Relationship to chest sonography

INTRODUCTION/OBJECTIVE

The aim of the study was to compare findings of transthoracic sonography (TS) and of spiral computed tomography (sCT) in patients with suspected pulmonary embolism (PE).

METHODS AND PATIENTS

Peripheral parenchymal and pleural findings of TS and sCT were compared in 62 patients (25 females, 37 males; mean age 62.2 years) with suspected PE.

RESULTS

In 39 patients PE was established, of whose pleura-based lesions could be detected by TS in 30 patients and by sCT in 31 patients. Whilst in three of the patients parenchymal lesions were exclusively detected by sonography, no peripheral abnormalities could be discovered with either technique in five patients. Among the nine patients lacking peripheral abnormalities on sonography, four revealed peripheral lesions in sCT. In 23 patients without PE, peripheral consolidations at CT were detected in six patients whereas two showed lesions on TS. With respect to the appearance, pleura-based wedge-shaped consolidations were the main parenchymal alterations (82.4% at TS, 66.1% at sCT) as compared with non-wedge-shaped consolidations (17.6% at TS, 33.9% at sCT). Peripheral lesions were located preferentially within the lower lobes. In addition, both localised and basal pleural effusion associated with PE could be demonstrated in 58.9% at TS and in 23.1% by sCT.

DISCUSSIONS AND CONCLUSION

The study shows that in PE parenchymal and pleural changes are detectable by TS and sCT. If parenchymal findings are present at sCT, peripheral PE should be considered, even in the absence of directly visible emboli.

CT perfusion image of the lung: value in the detection of pulmonary embolism in a porcine model

RATIONALE AND OBJECTIVES

We assess the value of computed tomography perfusion image (CTPI) obtained by postprocessing the CT data in the diagnosis of pulmonary embolism.

METHODS

An experimental pulmonary embolism model was made in 6 pigs by injecting 2 types of emboli into the pulmonary arteries. For each pig, 5 type-A (diameter 3.5 x 8 mm) and 5 type-B (diameter 2.5 x 6 mm) emboli were injected through a catheter with the distal tip located in the inflow tract of the right atrium. After obtaining precontrast and postcontrast CT data during a single breath-hold using a 4-slice multidetector CT, perfusion images were generated by data subtraction. Approximately 150 to 180 mL of contrast material was injected at an injection rate of 6 mL/s to obtain postcontrast CT. Three independent observers twice analyzed CT images for the presence of emboli: once with postcontrast CT scans (CT angiography: CTA) alone and again with both CTA and CTPI. The locations of the emboli in the pulmonary arteries were confirmed by examining the killed porcine lungs.

RESULTS

The sensitivity and positive predictive value in the detection of pulmonary emboli with CTA alone were 59% (106/180) and 87% (106/122), respectively. The sensitivity and positive predictive value with both CTA and CTPI were 87% (156/180) and 85% (156/184), respectively. For type-A emboli, the sensitivity with both CTA and CTPI (76/90, 85%) was better than that with CTA alone (63/90, 70%) (P < 0.001). For type-B emboli, the sensitivity with both CTA and CTPI (80/90, 89%) was also better than that of CTA alone (43/90, 48%) (P < 0.001).

CONCLUSIONS

CTPI could be obtained using digital subtraction of the CT data. It appeared to be an adjunct in enhancing the diagnostic accuracy of pulmonary embolism, particularly when detecting small pulmonary emboli.

Diagnóstico por imagem do tromboembolismo pulmonar agudo

O diagnóstico do tromboembolismo pulmonar agudo é baseado na probabilidade clínica, uso do dímero D (quando disponível) e na avaliação por imagem. Os principais métodos de imagem utilizados no diagnóstico são representados por cintilografia ventilação-perfusão, angiografia pulmonar e tomografia computadorizada (TC). Na última década vários estudos têm demonstrado que a TC espiral apresenta elevada sensibilidade e especificidade no diagnóstico de tromboembolismo pulmonar agudo. Uma melhor avaliação das artérias pulmonares tornou-se possível com a recente introdução dos equipamentos de TC espirais com multidetectores. Vários pesquisadores têm sugerido que a angiografia pulmonar por TC espiral deve substituir a cintilografia na avaliação de pacientes com suspeita clinica de tromboembolismo pulmonar agudo. Os autores discutem os principais métodos de imagem utilizados no diagnóstico de tromboembolismo pulmonar agudo enfatizando o papel da TC espiral.

Syncope in patients with pulmonary embolism: comparison between patients with syncope as the presenting symptom of pulmonary embolism and patients with pulmonary embolism without syncope

Syncope as an initial presentation of pulmonary embolism occurs in 10% of patients. We compared clinical and instrumental parameters in patients with syncope as the presenting symptom of pulmonary embolism and in patients with documented pulmonary embolism without syncope. Seventy patients with the diagnosis of pulmonary embolism and apparently stable clinical conditions were evaluated. They were divided in two groups: 10 patients with syncope as the presenting symptom of pulmonary embolism (group 1) and 60 patients without syncope (group 2). Patients with syncope showed a more pronounced tendency to present with main pulmonary artery embolus than patients without syncope (contingency coefficient = 0.301, p < 0.04; one-tailed). However, despite the evidence that patients with syncope have significant reductions in systolic and/or diastolic blood pressure, shock was not observed in any patient. In no case was thrombolytic treatment given and all patients received standard anticoagulation with unfractioned heparin and oral anticoagulant. We suggest that syncope in the setting of non-massive pulmonary embolism may be due to vaso-vagal mechanism that can lead to a reduction of arterial blood pressure when central artery thrombosis is involved.

[Mediastinal and abdominal lymphoedema: consequence of massive pulmonary embolism with shock?]

We report a case of severe pulmonary embolism diagnosed using spiral CT-scan in a patient admitted for shock associated with acute abdominal symptoms. Intraluminal clots images were visualized associated with an infiltration of mediastinal fat. Abdominal CT showed infiltration of the hepatobiliary hilum. After thrombolysis, the clinical thoracic and abdominal symptoms improved. A CT-scan at the 48(th) hour showed that the thoracic and abdominal features had disappeared. We emphasize the misleading aspect of the CT-scan images and we speculated that this infiltration could reflect the abdominal and mediastinal lymphoedema.

Computed tomography of acute pulmonary embolism

Pulmonary embolism (PE) is a common condition in which diagnostic and therapeutic delays contribute to substantial morbidity and mortality. Advances in spiral computed tomography (CT) scanner technology over the past 10 years have been paralleled by progressive improvement in the ability to identify and accurately evaluate the pulmonary arteries for acute PE using CT pulmonary angiography (CTPA). Preliminary studies indicate multi-detector CT (MDCT) scanners offer improved accuracy for distal segmental and subsegmental PE. The ability to directly visualize emboli using CTPA has led to its widespread implementation. Published studies using optimal techniques have found sensitivity and specificity of approximately 90%. Clinical signs and symptoms are nonspecific. Only 20% to 30% of those patients evaluated for acute PE are found to harbor emboli. Previous imaging algorithms offered limited diagnostic value for the remaining 70% to 80% of patients who proved not to have PE. It has been shown that spiral CT identifies an alternate diagnosis in approximately 70% of these patients, which, along with its rapid and widespread availability, largely accounts for its popularity with referring clinicians. It is noted that meta-analysis studies of the existing data regarding spiral CT in acute PE have shown deficiencies in study designs, indicating that further research is required. However, at this time, spiral CT is being widely employed in the diagnostic work-up of patients with suspected acute PE. This review will discuss the use of spiral CT for acute PE, including scan acquisition parameters, radiation dose, diagnostic findings, interpretive pitfalls and the role of leg vein studies.

Patient with bilateral pleural effusion: are the findings the same in each fluid?

STUDY OBJECTIVES

To determine whether, in patients with bilateral pleural effusions, the main cellular and biochemical features of the pleural fluid on the right side differ from or correlate with those on the left side. We examined lactate dehydrogenase (LDH), glucose, and total protein (TP) levels, RBC count, nucleated cell count (NCC), and differential cell count.

PATIENTS AND METHODS

Twenty-seven patients with bilateral pleural effusions, including 13 patients with effusions after coronary artery bypass graft surgery, 12 patients with congestive heart failure, 1 patient with malignant pericarditis, and 1 patient with renal failure, were studied retrospectively.

RESULTS

The right-sided and the left-sided pleural effusions did not differ in the mean TP (p = 0.38), glucose (p = 0.31), and LDH (p = 0.39) levels, RBC count (p = 0.31), NCC (p = 0.96), and the percentage of neutrophils (p = 0.22), lymphocytes (p = 0.73), mononuclear cells (MNCs) [p = 0.49], and eosinophils (p = 0.65). The bias +/- precision was 0.1 +/- 0.64 g/dL for TP, - 2.7 +/- 23 mg/dL for glucose, 41 +/- 362 IU/L for LDH, 6,100 +/- 62,900 cells/ micro L for RBC count, - 36 +/- 1,043 cells/ micro L for NCC, - 2.9 +/- 11.6% for the percentage of neutrophils, 1.15 +/- 17% for the percentage of lymphocytes, 2.3 +/- 17% for the percentage of the MNCs, and - 0.15 +/- 5.4% for the percentage of eosinophils. Moreover, there was a close correlation between the right-sided and the left-sided pleural effusions concerning TP level (r = 0.85, p < 0.001), glucose level (r = 0.78, p < 0.001), LDH level (r = 0.71, p < 0.001), RBC count (r = 0.66, p < 0.001), NCC (r = 0.60, p = 0.001), and the percentage of neutrophils (r = 0.77, p < 0.001), lymphocytes (r = 0.77, p < 0.001), MNCs (r = 0.74, p < 0.001), and eosinophils (r = 0.84, p < 0.001).

CONCLUSION

Since the pleural fluid findings tend to be similar in both sides of patients with bilateral pleural effusion, we suggest that diagnostic thoracentesis may not need to be performed on both sides, unless there is a specific clinical indication.

Six cases of acute central pulmonary embolism revealed on unenhanced multidetector CT of the chest

OBJECTIVE

Our purpose was to describe the imaging findings of central pulmonary embolism on unenhanced multidetector CT (MDCT) of the chest.

CONCLUSION

Unenhanced MDCT of the chest is often performed for the evaluation of nonspecific chest symptoms. Awareness of the rare finding of a high-attenuation centrally located pulmonary embolism on unenhanced MDCT is important because acute pulmonary embolism may be identified when it is not suspected clinically, and such detection can determine further imaging needs and allow the timely initiation of appropriate therapy.

CT pulmonary angiography and suspected acute pulmonary embolism

PURPOSE

To evaluate the use and quality of CT pulmonary angiography in our department, and to relate the findings to clinical parameters and diagnoses.

MATERIAL AND METHODS

A retrospective study of 324 consecutive patients referred to CT pulmonary angiography with clinically suspected pulmonary embolism (PE). From the medical records we registered clinical parameters, blood gases, D-dimer, risk factors and the results of other relevant imaging studies.

RESULTS

55 patients (17%) had PE detected on CT. 39 had bilateral PE, and 8 patients had isolated peripheral PE. 87% of the examinations showing PE had satisfactory filling of contrast material including the segmental pulmonary arteries, and 60% of the subsegmental arteries. D-dimer test was performed in 209 patients, 85% were positive. A negative D-dimer ruled out PE detected at CT. Dyspnea and concurrent symptoms or detection of deep vein thrombosis (DVT), contraceptive pills and former venous thromboembolism (VTE) were associated with PE. The presence of only one clinical parameter indicated a negative PE diagnosis (p < 0.017), whereas two or more suggested a positive PE diagnosis (p < 0.002). CT also detected various ancillary findings such as consolidation, pleural effusion, nodule or tumor in nearly half of the patients; however, there was no association with the PE diagnosis.

CONCLUSION

The quality of CT pulmonary angiography was satisfactory as a first-line imaging of PE. CT also showed additional pathology of importance in the chest. Our study confirmed that a negative D-dimer ruled out clinically suspected VTE.

Pulmonary embolus imaging with multislice CT

Multiple data support the concept that single-slice and multislice CT have fundamentally modified the diagnostic approach of patients with suspected PE. Although the definitive role of spiral CT angiography in the diagnostic algorithm has yet to be determined, it is clear that CT angiography has numerous advantages compared with other diagnostic tests. Bearing in mind that an effective diagnostic strategy should be as flexible as possible to be applied in every clinical setting, the role of spiral CT angiography in the diagnostic algorithm has to be considered among several practical parameters, such as the experience of the attending physician, degree of severity of the patient's clinical condition, the availability of diagnostic equipment, and specific logistics.

Imaging of acute pulmonary thromboembolism: should spiral computed tomography replace the ventilation-perfusion scan?

For several decades, ventilation-perfusion scintigraphy has been the main imaging modality used in the evaluation of patients with suspected acute pulmonary embolism (PE). Recently, various investigators have suggested that spiral CT pulmonary angiography should replace scintigraphy in the assessment of patients whose symptoms are suggestive of acute PE. This article discusses the role of the various imaging modalities in the diagnosis of acute PE and suggests a diagnostic imaging algorithm based on current evidence in the literature.

Detection of lung perfusion abnormalities using computed tomography in a porcine model of pulmonary embolism

The purpose of this study was to identify perfusion defects of the lung using computed tomography (CT). A balloon catheter was placed in a lobar pulmonary artery of six anesthetized, ventilated, juvenile pigs to simulate occlusive segmental embolus. Contrast medium was injected via a central venous catheter at rates of 1.5, 3, 4.5, and 9 ml/s in each pig. A 40-second single-level cine CT was acquired distal to the inflated balloon during suspended inspiration. Three computer-manipulated images (time to maximal enhancement, change in maximal attenuation, maximal contrast minus precontrast subtraction) were generated using custom software and compared with the unmodified maximal enhancement and precontrast images. Two independent observers identified perfusion defects and scored the level of confidence (5-point scale) on all five images. Regions of interest were drawn in perfused and nonperfused lung and time-attenuation curves were generated. Perfusion defects were accurately (99.8 +/- 0.3%) and confidently (4.5 +/- 0.6) detected and there was excellent interobserver agreement (Kappa 0.99 +/- 0.02) on all computer-manipulated images. There was a significant increase in confidence (p < 0.05) between contrast medium injection rates of 1.5 and 9 ml/s. A linear relationship exists (r = 0.88) between injection rate and change in maximal attenuation. In conclusion, perfusion defects of the lung are seen using computer-manipulated CT images.

Real-time chest ultrasonography: a comprehensive review for the pulmonologist

This review discusses real-time pulmonary ultrasonography (US) for the practicing pulmonologist. US supplements chest radiography and chest CT scanning. Major advantages include bedside availability, absence of radiation, and guided aspiration of fluid-filled areas and solid tumors. Pulmonary vessels and vascular supply of consolidations may be visualized without contrast. US may help to diagnose conditions such as pneumothorax, hemothorax, pleural or pericardial effusion, pneumonia, and pulmonary embolism in the critically ill patient who is in need of bedside diagnostic testing. The technique of US, which is cost-effective compared to CT scanning and MRI, may be learned relatively easily by the pulmonologist.

Air trapping on CT of patients with pulmonary embolism

OBJECTIVE

We evaluated the relationship of air trapping to mosaic perfusion in patients with pulmonary embolism.

SUBJECTS AND METHODS

Forty-one consecutive patients with suspected pulmonary embolism underwent expiratory CT followed by helical CT angiography. After excluding 12 patients who had airway disease or were smokers, we divided the patients into two groups: those with (n = 15) and without (n = 14) pulmonary embolism. For each patient, six expiratory images were evaluated for the presence of air trapping, and the corresponding six images from CT angiography were evaluated for the presence of mosaic perfusion. Clot locations were assessed on CT angiography and were correlated with the presence of air trapping and mosaic perfusion.

RESULTS

In patients with pulmonary embolism, mosaic perfusion was identified in 32 areas (seven patients, 46.7%), and air trapping was identified 68 areas (nine patients, 60%). Of the 32 areas of mosaic perfusion, 23 areas (71.9%) showed air trapping on expiratory CT scans. Of the 68 areas with air trapping on expiratory scans, 23 areas (33.8%) showed mosaic perfusion on inspiratory scans, and 44 areas (64.7%) had clots in the arteries leading to them. Clots were more frequently identified in areas of lower attenuation on inspiratory CT scans and air trapping (21/23) than in those of normal attenuation on inspiratory CT scans and air trapping (23/45) (p < 0.005). Only one patient without pulmonary embolism had air trapping (p < 0.005).

CONCLUSION

Air trapping is common in pulmonary embolism and may be the cause of mosaic perfusion. Air trapping can be seen distal to vessels not showing pulmonary embolism.

Major pulmonary embolism: review of a pathophysiologic approach to the golden hour of hemodynamically significant pulmonary embolism

Major pulmonary embolism (PE) results whenever the combination of embolism size and underlying cardiopulmonary status interact to produce hemodynamic instability. Physical findings and standard data crudely estimate the severity of the embolic event in patients without prior cardiopulmonary disease (CPD) but are unreliable indicators in patients with prior CPD. In either case, the presence of shock defines a threefold to sevenfold increase in mortality, with a majority of deaths occurring within 1 h of presentation. A rapid integration of historical information and physical findings with readily available laboratory data and a structured physiologic approach to diagnosis and resuscitation are necessary for optimal therapeutics in this "golden hour." Echocardiography is ideal because it is transportable, and is capable of differentiating shock states and recognizing the characteristic features of PE. Spiral CT scanning is evolving to replace angiography as a confirmatory study in this population. Thrombolytic therapy is acknowledged as the treatment of choice, with embolectomy reserved for those in whom thrombolysis is contraindicated.

CT of pulmonary thromboembolic disease

A good quality CT pulmonary angiogram has a high accuracy rate for the evaluation of pulmonary embolism. Investigators have reported that the subsegmental emboli can be missed; however, visualization of smaller arterial branches, and therefore, detection of small emboli may improve with the availability of multidetector scanners. Some of the advantages of using CT for pulmonary embolism compared with lung scintigraphy include: (1) direct visualization of emboli on CT, (2) evaluation of lung parenchyma and mediastinum, which may provide an alternate diagnosis, and (3) capability to acquire CT venogram without additional contrast with "one-stop examination" for evaluation of thromboembolic disease.

Computed tomography scan versus ventilation-perfusion lung scan in the detection of pulmonary embolism

This study compared the sensitivity and specificity of computed tomography (CT) scan and ventilation-perfusion (V-P) scan in detecting pulmonary embolism (PE) with pulmonary angiogram (AG) as the reference standard. Following a comprehensive search of the indexed medical literature, CT scan studies related to PE diagnosis were systematically evaluated to select those using AG as the reference standard and meeting specified methodologic criteria. Studies were further grouped by those reporting results for central PE findings only versus central and peripheral PE combined. A composite analysis of data derived from seven selected publications yielded sensitivity and specificity estimates for CT scan in detecting PE, which were statistically compared to the published results of a multi-center study reporting the sensitivity and specificity of the V-P scan with pulmonary AG as the reference standard. The calculated CT scan sensitivity was 77% for central PE only data and 81% for central and peripheral PE combined data, and the CT scan specificity was 91% and 98%, respectively. High-probability V-P scan sensitivity was 41% and specificity 97%; high- and intermediate-probability V-P scans combined yielded sensitivity 83% and specificity 52%. The sensitivity for PE detection was significantly greater for CT scan than for high-probability V-P scan; CT scan sensitivity was equivalent to V-P when high- and intermediate-probability scans were considered together. CT scan specificity for central and peripheral PE combined was equivalent to that of the high-probability V-P scan, but significantly greater than that of high- and intermediate-probability V-P scans considered together. Considering that only a small proportion of patients with suspected PE yield high-probability V-P scan results (which are usually indicative of PE), while as many as one-half of patients may yield intermediate-probability results (which are commonly not useful in PE diagnosis), our results suggest the CT scan may be an appropriate study for use by Emergency Physicians in the clinical evaluation of suspected PE.

Pleural effusion due to pulmonary emboli

Pulmonary embolism is the fourth leading cause of pleural effusion. The possibility of pulmonary embolus should be evaluated for all patients who have undiagnosed pleural effusion. The mechanism of pleural effusion caused by pulmonary embolus is usually increased interstitial fluid in the lungs as a result of ischemia or the release of vasoactive cytokines. Approximately 75% of patients with pulmonary emboli and pleural effusion have pleuritic chest pain. The most common cause of pleuritic chest pain and pleural effusion in patients under 40 years old is pulmonary emboli. Pleural effusion resulting from a pulmonary embolus usually occupies less than one-third of the hemithorax. Dyspnea is frequently out of proportion to the size of the pleural effusion. Pleural fluid caused by pulmonary emboli is usually exudative but is occasionally transudative. d-Dimer testing is a good screen for pulmonary emboli. If d-dimer results are positive, then a spiral computed tomograph should be obtained to confirm the diagnosis. Low-molecular-weight-heparin has become the initial treatment of choice for patients with pulmonary emboli and pleural effusion.

Pulmonary embolism: comparison of gadolinium-enhanced MR angiography with contrast-enhanced spiral CT in a porcine model

RATIONALE AND OBJECTIVES

The purpose of this study was to compare gadolinium-enhanced magnetic resonance (MR) angiography with contrast material-enhanced computed tomography (CT) for the detection of small (4-5-mm) pulmonary emboli (PE), with a methacrylate cast of the porcine pulmonary vasculature used as the diagnostic standard.

MATERIALS AND METHODS

In 15 anesthetized juvenile pigs, colored methacrylate beads (5.2 and 3.8 mm diameter-the size of segmental and subsegmental emboli in humans) were injected via the left external jugular vein. After embolization, MR angiographic and CT images were obtained. The pigs were killed, and the pulmonary arterial tree was cast in clear methacrylate, allowing direct visualization of emboli. Three readers reviewed CT and MR angiographic images independently and in random order.

RESULTS

Forty-nine separate embolic sites were included in the statistical analysis. The mean sensitivity (and 95% confidence intervals) for CT and MR angiography, respectively, were 76% (68%-82%) and 82% (75%-88%) (P > .05); the mean positive predictive values, 92% (85%-96%) and 94% (88%-97%) (P > .05). In this porcine model, PE were usually seen as parenchymal perfusion defects (98%) with MR angiography and as occlusive emboli (100%) with CT.

CONCLUSION

MR angiography is as sensitive as CT for the detection of small PE in a porcine model.

Spiral CT findings in septic pulmonary emboli

OBJECTIVES

The aim of the study was to determine the characteristics of septic pulmonary emboli and their prevalence on spiral computed tomographic (CT) scans.

METHODS AND MATERIALS

We evaluated 65 lesions on spiral CT scans in ten patients with septic pulmonary emboli. Spiral CT scans (10-mm collimation) were obtained at 10-mm intervals from the lung apex to the diaphragm and were compared with posteroanterior chest radiographs obtained within 24 h after CT scanning.

RESULTS

Only 21 (32%) of the 65 lesions detected on CT scans were also detected on chest radiographs. Peripheral nodules (39 lesions (60%)) were seen in all ten patients, wedge-shaped peripheral lesions (15 lesions (23%)) in nine patients, and infiltrates (11 lesions (17%)) in four patients. Subpleural lesions (45 lesions (69%)) and feeding vessels (35 (54%)) were found in all patients, and cavitary lesions (seven lesions (11%)) were seen in four patients. Subpleural peripheral nodules and wedge-shaped peripheral lesions were seen in nine patients. Thirty-two lesions (49%) ranged in diameter from 10 to 19 mm, and 59 lesions (91%) were less than 30 mm.

CONCLUSIONS

Spiral CT is useful in detecting septic pulmonary emboli. On spiral CT subpleural peripheral nodules and wedge-shaped peripheral lesions less than 30 mm in diameter are often found in patients with septic pulmonary emboli.

New diagnostic tests for pulmonary embolism

In 1990, the multicenter Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), sponsored by the National Institutes of Health, compared the diagnostic value of the radioisotopic ventilation-perfusion lung scan (V/Q scan) with that of pulmonary angiography for the diagnosis of pulmonary embolism (PE). Despite the endurance of the radioisotopic V/Q scan as the most widely used test for evaluation of pulmonary embolism (PE), a better screening tool is clearly needed for use in the emergency department. During the past decade, several new modalities have emerged for evaluation of patients with suspected PE. We evaluate the diagnostic utility of the D-dimer test and the alveolar dead space determination as potential screening tests and of spiral computed tomography, magnetic resonance imaging, transthoracic echocardiography, and transesophageal echocardiography as potential confirmatory tests for PE. For comparison, recent data on the diagnostic utility of the alveolar-arterial oxygen gradient and the V/Q scan are included. The potential application of these new tests to a hypothetical ED population is described.

Sensitivity and specificity of helical computed tomography in the diagnosis of pulmonary embolism: a systematic review

PURPOSE

To determine the sensitivity and specificity of helical computed tomography (CT) for the diagnosis of pulmonary embolism and to determine the safety of withholding anticoagulant therapy in patients who have clinically suspected pulmonary embolism and negative results on helical CT.

DATA SOURCES

The MEDLINE database was searched for all reports published from 1986 to October 1999 that evaluated the use of helical CT for the diagnosis of pulmonary embolism. Bibliographies of the retrieved articles were cross-checked to identify additional studies.

STUDY SELECTION

All prospective English-language studies were selected. Retrospective studies, review articles, and case reports were excluded, and 5 of the 20 identified articles were excluded. The scientific validity of the remaining 15 articles was assessed.

DATA EXTRACTION

Two of the authors used a priori, pre-defined criteria to independently assess each study. A third author resolved disagreements by adjudication. The pre-defined criteria were inclusion of a consecutive series of all patients with suspected pulmonary embolism, inclusion of patients with and those without pulmonary embolism, a broad spectrum of patient characteristics, performance of helical CT and pulmonary angiography (or an appropriate reference test) in all patients, and independent interpretation of the CT scan and pulmonary angiogram (or reference test). Specific data on sensitivity and specificity and the associated 95% CIs were recorded when available.

DATA SYNTHESIS

No study met all of the predefined criteria for adequately evaluating sensitivity and specificity. The reported sensitivity of helical CT ranged from 53% to 100%, and specificity ranged from 81% to 100%. In no prospective study was anticoagulant therapy withheld without further testing for venous thromboembolism in consecutive patients with suspected pulmonary embolism. One prospective study reported the outcome of selected patients with negative results on helical CT who did not receive anticoagulant therapy.

CONCLUSIONS

Use of helical CT in the diagnosis of pulmonary embolism has not been adequately evaluated. The safety of withholding anticoagulant treatment in patients with negative results on helical CT is uncertain. Definitive large, prospective studies should be done to evaluate the sensitivity, specificity, and safety of helical CT for diagnosis of suspected pulmonary embolism.

Spiral computed tomography for pulmonary embolism

Spiral computed tomography pulmonary angiography is increasingly used in the non-invasive investigation of patients with suspected pulmonary embolism. This review will focus on current techniques and indications with an explanation of the computed tomography signs of pulmonary embolism, possible pitfalls in interpretation and limitations of the technique.

Imaging evaluation of suspected pulmonary embolism

Venous thromboembolism (VTE) is a common disorder that is difficult to diagnose clinically but carries significant morbidity and mortality if untreated. Additionally, although demonstrated to be of benefit in cases of proven deep vein thrombosis (DVT) and pulmonary embolism (PE), anticoagulation therapy is not without risk. Because the clinical exam is known to be unreliable for the detection of both DVT and PE, many imaging modalities have been used in the diagnostic imaging algorithm for the detection of VTE, including chest radiography, ventilation/perfusion (V/Q) scintigraphy, pulmonary angiography, and recently, spiral computed tomography (CT) and magnetic resonance imaging (MRI). Chest radiographic findings in acute PE include focal oligemia, vascular enlargement, atelectasis, pleural effusions, and air space opacities representing pulmonary hemorrhage or infarction. The chest radiograph can occasionally be suggestive of PE but is more often nonspecifically abnormal. The main use of the chest radiograph in the evaluation of suspected PE is to exclude entities that may simulate PE and to assist in the interpretation of V/Q scintigraphy. Lower extremity venous compression ultrasonography (CU) is both sensitive and specific for the diagnosis of femoropopliteal DVT, and the value of negative CU results has been established in outcomes studies. However, the reliability of CU for the detection of isolated calf vein thrombosis is not well established, and the clinical significance of such thrombi is debatable. Additional methods such as color and spectral Doppler analysis are also useful in the diagnostic evaluation of DVT but are best considered as adjuncts to the conventional CU examination rather than as primary diagnostic modalities themselves. Compression ultrasonography and Doppler techniques are useful in the evaluation of suspected upper extremity DVT; spectral Doppler waveform analysis is particularly useful to assess for the patency of veins that cannot be directly visualized and compressed with conventional gray-scale sonography. V/Q scintigraphy has been the initial modality obtained in patients suspected of PE for a number of years. Although many studies have investigated the role of V/Q scintigraphy in the evaluation of VTE, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study has provided the most useful information regarding the utility of V/Q scintigraphy in this setting. A high probability scan interpretation is sufficient justification to institute anticoagulation, and a normal perfusion scan effectively excludes the diagnosis of PE. A normal/near normal scan interpretation also carries a sufficiently low prevalence of angiographically proven PE to withhold anticoagulation. Although the prevalence of PE in the setting of low probability scan interpretations is low and several outcomes studies have demonstrated a benign course in untreated patients with low probability scan results, patients with inadequate cardiopulmonary reserve do not necessarily have good outcomes. Such patients deserve more aggressive evaluation. Patients with intermediate probability scan results have a 20% to 40% prevalence of angiographically proven PE and thus require further investigation. The radionuclide investigation of DVT includes such techniques as radionuclide venography and thrombus-avid scintigraphy. Although these methods have not been as thoroughly evaluated as CU, studies thus far have indicated encouraging results, and further investigations are warranted. Pulmonary angiography has been the gold standard for the diagnosis of PE for decades. Studies have indicated that angiography has probably been underutilized by referring physicians for the evaluation of suspected PE, likely because of the perception of significant morbidity and mortality associated with the procedure. (ABSTRACT TRUNCATED)

Spiral CT angiography of the pulmonary circulation

Spiral computed tomographic (CT) angiography of the pulmonary circulation has emerged recently as a potential useful diagnostic method for the evaluation of the pulmonary circulation. As a minimally invasive examination, this technique is becoming widely available and has progressively replaced conventional and digital pulmonary angiography as the standard diagnostic imaging modality of the pulmonary circulation. The purpose of this review is to capture the current state of the art of the technical aspects of spiral CT angiography, with special emphasis on the post-processing techniques currently available. As CT is responsible for a considerable part of the medical radiation dose applied to the population, the current trends for dose saving will also be emphasized. With regard to the clinical applications of spiral CT angiography, its introduction into the diagnostic work-up of pulmonary embolism has considerably modified the diagnostic algorithms. Our 8-year review of the literature presented herein is expected to provide the readers with a basis for formulating an informed opinion on this topic. In addition, a large number of congenital and acquired disorders of the pulmonary circulation are also relevant to this technique, and these indications are discussed in the context of the corresponding therapeutic options. Owing to the multiple possibilities inherent to this technique, spiral CT has the potential for cost savings without reduction in image quality or diagnostic accuracy.

Spiral CT of acute pulmonary thromboembolism: evaluation of pleuroparenchymal abnormalities

PURPOSE

The goal of this work was to identify and categorize the spectrum of pulmonary parenchymal and pleural abnormalities identified by CT in patients with acute pulmonary thromboembolism (PE).

METHOD

A review of interpretations from 4,715 consecutive contrast-enhanced thoracic CT studies identified 41 examinations in which the diagnosis of PE was reported. Thirty-four studies were available for review, and two radiologists confirmed intraluminal defects in 31 patients. The number of emboli were counted and localized using bronchopulmonary nomenclature. Associated parenchymal and pleural abnormalities were tabulated.

RESULTS

Of the 31 patients, 13 underwent confirmatory or correlative studies including angiography, radionuclide study, or autopsy. In addition, deep venous thrombosis was confirmed by ultrasound or MRI in 13 patients. An average of 7.5 emboli per patient was detected. Pleuroparenchymal findings were as follows: Nine patients (29%) had no acute pulmonary parenchymal or pleural abnormality. In the remaining 22 patients, pleural effusion was the most common abnormality, found in 14 of 31 (45%). Ten patients (32%) had peripheral wedge-shaped parenchymal opacities suggestive of pulmonary infarction. Normally enhancing lobar atelectasis was seen in nine patients (29%). Six patients (19%) demonstrated heterogeneous parenchymal enhancement within nonaerated lung, two of whom had pathologically proven pulmonary infarct. Thirteen of 31 patients underwent high resolution CT; a typical mosaic perfusion pattern was seen in only 1 patient.

CONCLUSION

Twenty-nine percent of patients with acute PE had no acute lung parenchymal abnormality on CT; thus, the absence of parenchymal abnormality on CT does not exclude PE. High resolution CT mosaic perfusion was not a common feature of acute pulmonary embolism. Regions of decreased enhancement within nonaerated lung, seen in 19%, may prove to be an indicator of pulmonary infarction; however, this is a nonspecific finding.

Parenchymal and pleural findings in patients with and patients without acute pulmonary embolism detected at spiral CT

PURPOSE

To compare the frequencies of parenchymal abnormalities and pleural effusions in patients with and patients without acute pulmonary embolism (PE) detected at spiral computed tomography (CT).

MATERIALS AND METHODS

Contrast material-enhanced spiral CT scans obtained in 92 patients clinically suspected of having acute PE were retrospectively reviewed. The presence or absence of parenchymal abnormalities and pleural effusions was noted. The presence of filling defects consistent with central or peripheral PE was recorded.

RESULTS

Twenty-eight patients had CT evidence of PE. Central emboli were evident in 27 (96%) of these patients; 23 (82%) had concomitant central and peripheral emboli, and four (14%) had only central emboli. One patient had an isolated subsegmental clot. Parenchymal abnormalities were seen in 24 (86%) patients with PE and 56 (88%) patients without PE. Atelectasis, the most common finding, was present in 20 (71%) patients with PE and 41 (64%) patients without PE. The only parenchymal abnormality significantly associated with PE was peripheral wedge-shaped opacity, which was seen in seven (25%) patients with PE and three (5%) patients without PE (odds ratio, 6.78; 95% CI = 1.60, 28.62). Pleural effusions were seen in 16 (57%) patients with PE and 36 (56%) patients without PE. In 25 (39%) patients without PE, there were additional CT findings that might suggest an alternative explanation for the acute clinical presentation.

CONCLUSION

Parenchymal and pleural findings at CT are of limited value for differentiating patients with PE from those without PE.