Ventilation-perfusion studies in suspected pulmonary embolism.

The results of ventilation-perfusion (V-Q) imaging and pulmonary angiography were retrospectively analyzed in 146 patients with suspected pulmonary embolism (PE) to define the frequency of PE associated with various scintigraphic patterns. When the radionuclide images demonstrated at least two moderate-sized or one large area of V-Q mismatch, the probability of PE was 92%. However, only one of three patients with a single moderate-sized V-Q mismatch had PE, while small V-Q mismatches were not associated with PE in any of 19 patients. Matched V-Q abnormalities in lung regions that were radiographically normal were infrequently due to PE (4.8%). When a perfusion defect was substantially smaller than a corresponding radiographic abnormality, the frequency of PE was low (7.7%). Conversely, when a perfusion defect was substantially larger than the corresponding radiographic abnormality, there was a high probability of PE (87%). Matched perfusion and radiographic abnormalities indicated an intermediate probability of PE (27%). Patients with suspected pulmonary embolism may be classified into groups with low, intermediate, or high probability of pulmonary embolism on the basis of size and number of perfusion defects and a careful comparison of perfusion defects with ventilatory and radiographic findings.     

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.     

Spiral CT for suspected pulmonary embolism

Fitzgerald, Dr R. (2000). Clinical Radiology55, 983.     

Perfusion SPECT in patients with suspected pulmonary embolism

Purpose

Ventilation/perfusion tomography (V/P_SPECT), with new interpretation criteria and newer tracers for ventilation imaging, has markedly improved the diagnostic yield in acute pulmonary embolism (PE). Here, we evaluated the diagnostic performance of perfusion SPECT (P_SPECT) without ventilation imaging.

Methods

We studied 152 patients with clinically suspected PE who had been examined with both V/P_SPECT and multidetector computed tomographic angiography (MD-CTA). The diagnosis or exclusion of PE was decided by the referring clinician based on both the V/P_SPECT and/or MD-CTA findings in combination with the clinical findings. P_SPECT images were retrospectively examined by a physician with experience in the interpretation of planar perfusion scans who was blinded to clinical, V/P_SPECT and MD-CTA data. P_SPECT images were interpreted without the aid of chest radiography. All the patients who were deemed to have PE were given anticoagulant therapy.

Results

Of the 152 patients, 59 (39 %) received a final diagnosis of PE, and 19 (32 %) had associated cardiopulmonary diseases such as pneumonia, COPD, or left heart failure. P_SPECT correctly identified 53 (90 %) of the 59 patients with PE. The specificity was 88 of 93 (95 %). None of the P_SPECT images was rated nondiagnostic. P_SPECT yielded an overall diagnostic accuracy of 93 % (95 % confidence interval, CI, 87–96 %). At the observed PE prevalence of 39 %, the positive and negative predictive values of P_SPECT were 91 % (95 % CI, 80–97 %) and 94 % (95 % CI, 86–97 %), respectively.

Conclusion

In managing critically ill patients, P_SPECT might be a valid alternative to V/P_SPECT or MD-CTA since it was able to identify most patients with PE with a low false-positive rate and no inconclusive results.     

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)     

Pretest risk assessment in suspected acute pulmonary embolism

RATIONALE AND OBJECTIVES: To assess the pretest practices of US clinicians who treat patients with acute pulmonary embolism (PE). MATERIALS AND METHODS: We surveyed 855 practicing physicians selected randomly from three professional organizations. We asked participants to estimate how often and by what method they determine the likelihood of PE before they request confirmatory studies. Participants reported their awareness of four published clinical practice guidelines dealing with acute PE and selected options for further diagnostic testing after reviewing clinical data from three hypothetical patients presenting with low, intermediate, and high probability of acute PE. RESULTS: We received completed surveys from 240 physicians practicing in 44 states. Although most (98.3%) report that they assess pretest probability of PE before testing, slightly more than half do so routinely. A total of 72.5% prefer an unstructured approach to pretest assessment, whereas 22.9% use published prediction rules. Most (93.0%) are aware of at least one published guideline for assessing acute PE, but only 44.2% report using one or more in daily practice. Respondents who use published prediction rules, estimate pretest probability routinely, or use at least one practice guideline were more likely to request additional testing when reviewing a low probability clinical scenario. No differences in testing frequency or preferences were observed for intermediate or high probability clinical scenarios. CONCLUSIONS: The majority of clinicians we surveyed use an unstructured approach when estimating the pretest probability of acute PE. With the exception of low probability scenario, clinicians agreed on testing choices in suspected acute PE, regardless of the method or frequency of pre-test assessment.     

Isolated unilateral absence of pulmonary artery mimicking chronic pulmonary embolism at chest X-ray: multidetector-row CT angiographic findings

Unilateral absence of pulmonary artery (UAPA) is a rare congenital anomaly which can seldom be isolated (1:200,000) and incidentally discovered in adulthood. We describe the case of a 54-year-old male patient who was found to have isolated UAPA (IUAPA) during the clinical and radiological investigation of a single episode of hemoptysis. Although abnormal, chest X-ray findings differed considerably from those previously reported and the diagnosis was only achieved by multidetector-row computed tomography angiography and later confirmed by bed-side echocardiography. Further clinical and instrumental investigation revealed systemic hypertension (158/95 mmHg) and bilateral mild hydronephrosis which both remitted after transurethral prostatic adenomyomectomy.     

MDCT of 220 consecutive patients with suspected acute pulmonary embolism: incidence of pulmonary embolism and of other acute or non-acute thoracic findings

PURPOSE: This study was undertaken to evaluate the incidence of pulmonary embolism (PE) and other clinically relevant thoracic findings discovered on contrast-enhanced multidetector computed tomography (MDCT) examination in patients with a suspicion of acute PE. MATERIALS AND METHODS: We retrospectively reviewed 220 reports of 40-row MDCT exams in consecutive patients (101 men, 119 women; mean age 55 years+/-18) suspected for acute PE. Presenting symptoms and risk factors were recorded. Image quality and incidence of PE and other clinically relevant thoracic findings were evaluated. RESULTS: MDCT were diagnostic in 96.8% of patients. Nineteen patients (8.6%) were positive for PE. Signs and symptoms were present in 82.7% (182) and risk factors in 38.2% (84) of the population. Clinically relevant thoracic findings were detected in 45.9% (101) of the patients. Ten patients had PE and other thoracic findings. Half of the patients (110) had neither PE nor other clinically relevant thoracic findings. CONCLUSIONS: Chest MDCT, with an excellent overall image quality, provided an explanation for the clinical presentation in about 50% of emergency department patients studied and was useful in detecting PE and other thoracic diseases with symptoms mimicking PE. However, half of the exams were negative.     

Comparison of scintigraphic diagnostic criteria in suspected pulmonary embolism

Various criteria have been proposed for the interpretation of ventilation and perfusion (V/Q) scintigrams in diagnosing pulmonary thromboembolism. The Biello criteria, with modifications, have been a standard for years but they differ from the criteria currently being used in the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) trial. We carried out a retrospective study in an attempt to establish if one or the other set of criteria is better. Between February 1985 and September 1987, 38 patients had a V/Q scan for suspected pulmonary embolism and subsequently underwent pulmonary angiography. The V/Q scans were reviewed by two observers using the modified Biello and the PIOPED criteria. Receiver-operated characteristic curves were constructed separately for each set of criteria. Statistical analysis revealed that neither set of criteria was significantly better than the other, but the PIOPED criteria were felt to be better defined and easier to use. This may have implications for the practical application of the criteria.     

Unusual radiographic findings in adult pulmonary tuberculosis

To determine the frequency of unusual chest radiographic findings in adults (older than 15 years) with pulmonary tuberculosis, charts and radiographs of 270 consecutive cases seen in a 12 month period were reviewed. Radiographic findings not typical of primary or postprimary disease (reinfection) were arbitrarily classified as unusual. The incidence of such findings (8%) was considerably lower than in several recent reports (25%, 29%). Likewise, the incidence of lower lobe tuberculosis in diabetics in this population (8.3%) was lower than in a report by Weaver (20%), and the finding of air-fluid levels in patients with cavitary disease (9%) was lower than a report by Cohen (22%). Possible explanations for these discrepancies were reviewed, including: (1) demographic characteristics, (2) the patient selection process, (3) the arbitrary nature of any system of classification of "unusual" findings, and (4) the change in the epidemiology of the disease as a result of chemotherapy and organized eradication programs. Of these, the patient selection process is probably the most significant factor in the discrepancy between the incidence of unusual findings in this series compared with those reported by others.     

Scintigraphic probability and angiographic diagnostic certainty in acute pulmonary embolism

The objectives of this study were to determine if diagnostic certainty on angiography correlates with scintigraphic probability for the diagnosis of pulmonary embolism. From a total of 160 consecutive patients who underwent both nuclear imaging and invasive selective pulmonary angiography, we reviewed the xenon-133 ventilation images in 2 posterior oblique views and the Tc-99m macroaggregated serum albumin perfusion scans and angiograms of 40 patients (15 men, 25 women; average age 57 years) who were discharged from the hospital on anticoagulants with a diagnosis of pulmonary embolism. The angiograms were reviewed and the diagnosis of embolism was considered certain in the presence of an intraluminal filling defect, a trailing embolus, or a branch occlusion equal to or larger than a segmental branch (n=29; 73%), and uncertain when the studies were reinterpreted as either equivocal or negative or in the presence of a single, small subsegmental filling defect of questionable clinical significance. The ventilation-perfusion scans were read as high (n=18; 45%), intermediate (n=10; 25%), or low (n=12; 30%) probability. The proportion of patients with diagnostic certainty on angiography in the high-, intermediate-, and low-probability scintigraphic subgroups was, respectively, 100% (18 of 18), 70% (7 of 10), and 33% (4 of 12) (P=0.004). In patients diagnosed with pulmonary embolism based on selective angiography, a lower probability of pulmonary embolism on ventilation-perfusion scintigraphy correlates with a lesser degree of diagnostic certainty on angiography and a higher incidence of single subsegmental emboli.     

Single perfusion defect and pulmonary embolism: angiographic correlation

One hundred and thirty-three ventilation-perfusion scans (V-P) with angiographic correlation were retrospectively reviewed to evaluate the frequency of pulmonary emboli (PE) in single perfusion defects (SPD), regardless of ventilation or radiographic findings. By angiography, 15 of 30 SPD cases had PE. Demographic data and clinical presentation were similar for PE and non-PE patients. However, 9 out of 15 patients with PE had recent surgery compared to none of the non-PE patients. SPD were seen in areas of ventilation and chest x-ray abnormalities in 12 of 15 PE and 11 of 19 non-PE cases. Size of the actual lesion was underestimated by scintigraphy in most cases. In 7 of 15 PE cases, the perfusion defect was larger than the corresponding ventilation abnormality. Most SPD were located at the bases. Twelve of 15 SPD in the PE group were at the posterior basilar segment. In the appropriate clinical setting, SPD carries at least a moderate probability for PE. When the clinical suspicion is high, a pulmonary angiography will be needed to confirm the diagnosis.