The effect of imaging modality on patient management in the evaluation of pulmonary thromboembolism

Acute pulmonary embolism multimodality imaging prior to endovascular therapy

The manuscript discusses the application of CT pulmonary angiography, ventilation–perfusion scan, and magnetic resonance angiography to detect acute pulmonary embolism and to plan endovascular therapy. CT pulmonary angiography offers high accuracy, speed of acquisition, and widespread availability when applied to acute pulmonary embolism detection. This imaging modality also aids the planning of endovascular therapy by visualizing the number and distribution of emboli, determining ideal intra-procedural catheter position for treatment, and signs of right heart strain. Ventilation–perfusion scan and magnetic resonance angiography with and without contrast enhancement can also aid in the detection and pre-procedural planning of endovascular therapy in patients who are not candidates for CT pulmonary angiography.

Managing pulmonary embolism secondary to suppurative deep vein thrombophlebitis due to community-acquired Staphylococcus aureus in a resource-poor setting

Deep vein thrombosis and pulmonary thromboembolism are rare and life threatening emergencies in children. We report an 11-year old female who presented with acute complaints of high grade fever, pain in the left thigh and inability to walk and breathlessness since 6 days. On physical examination, there was a diffuse tender swelling of the left thigh, tachypnea, tachycardia with hyperdynamic precordium and bilateral basal crepitations. Ultrasonography and venous doppler of lower limbs showed mild effusion of left hip joint and thrombus in the left common femoral vein and left external iliac vein suggesting a diagnosis of septic arthritis with thrombophlebitis. The tachypnea and tachycardia which was out of proportion to fever and crepitations on auscultation prompted suspicion of an embolic phenomenon. Radiograph of the chest revealed multiple wedge shaped opacities in the right middle zone and lower zone suggestive of pulmonary embolism and left lower zone consolidation. For corroboration, computed tomography pulmonary angiography and computed tomography of abdomen was performed which showed pulmonary thromboembolism and deep venous thrombosis extending up to infrarenal inferior vena cava. On further workup, magnetic resonance imaging of hips showed left femoral osteomyelitis and multiple intramuscular abscesses in the muscles around the hip joint. Blood culture grew methicillin resistant Staphylococcus aureus. Antibiotics were changed according to culture sensitivity and there was a dramatic response. After four weeks of anticoagulation and antibiotics the child became asymptomatic and thrombus resolved. Thus, it is crucial to consider methicillin resistant Staphylococcus aureus infection as an important infection when we encounter such a clinical scenario. This case report highlights an unusual and potentially life threatening presentation of a virulent strain of a common pathogen, which when diagnosed was completely amenable to treatment.

Internal Barium Shielding to Minimize Fetal Irradiation in Spiral Chest CT: A Phantom Simulation Experiment

PURPOSE

To use a phantom to prospectively examine the attenuating effect of barium sulfate as an internal shield to protect the fetus.

MATERIALS AND METHODS

In an adult-size phantom, 1- and 2-cm-thick acrylic slabs containing 315 or 630 mL of water, 2% or 40% barium sulfate suspension, and a 1-mm lead sheet were placed under the diaphragm. In 17 experiments, fetal dose was measured by using thermoluminescent dosimeters that were placed immediately under (near field) and 10 cm below (far field) the water slab (eight experiments), barium sulfate slab (eight experiments), and lead sheet (one experiment). In a pulmonary embolism protocol, the phantom was scanned with single-detector spiral computed tomography (CT) at 130 kVp and 230 mAs.

RESULTS

The control radiation dose was 3.60 mSv+/-0.54 (standard deviation) with the water slab at near field, where the uterus dome is at near term, and 0.507 mSv+/-0.07 with the water slab at far field, the uterus position during early gestation. Scattered radiation was attenuated 13% and 21% with 2% barium sulfate and 87% and 96% with 40% barium sulfate, as calculated in the near and far fields, respectively, and 99% with the 1-mm lead sheet. The extrapolated attenuations for 5%-40% barium sulfate suspensions indicated that beyond a 30% suspension, attenuation increased further only slightly.

CONCLUSION

Study results in the phantom experiment suggest that fetal irradiation during maternal chest CT can be reduced substantially with barium shielding.

The Indeterminate CT Pulmonary Angiogram: Imaging Characteristics and Patient Clinical Outcome

PURPOSE

To retrospectively review imaging characteristics of indeterminate computed tomographic (CT) pulmonary angiograms for pulmonary embolism (PE) and patient outcome.

MATERIALS AND METHODS

Investigational review board approval was obtained, informed consent was waived, and the study was HIPAA compliant. Retrospective review of 3612 CT pulmonary angiography reports created between July 1, 2001, and July 1, 2003, was performed with a keyword search for "indeterminate," "nondiagnostic," or "inadequate" (thereafter, all defined as "indeterminate") and yielded studies from 237 patients (mean age, 57 years; 117 men, 120 women). Randomly selected diagnostic studies were used to form a control group of 25 subjects (mean age, 64 years; eight men, 17 women). Electronic medical records were reviewed for follow-up imaging (repeat CT pulmonary angiography, conventional pulmonary angiography, ventilation-perfusion scintigraphy, or lower-extremity ultrasonography [US]), use of anticoagulation, placement of inferior vena cava (IVC) filters, clinical outcomes, and comments regarding indeterminate reading of CT angiograms. Studies (in patients and control subjects) were reviewed for PE, contrast attenuation in the main pulmonary artery (MPA), motion artifacts, image noise, and flow artifacts. Findings were compared with two-sample t tests assuming unequal variance.

RESULTS

The cause cited for indeterminism was most often motion (74%), followed by poor contrast enhancement (40%). Contrast attenuation in the MPA was 245 HU +/- 80 (standard deviation) in patients and 339 HU +/- 88 in control subjects (P < .001). Only 46% of indeterminate studies met institutional criteria for adequate contrast attenuation in the MPA. Rereview of studies demonstrated five missed PEs. A total of 81 patients (33%) underwent follow-up imaging within 5 days, with one positive pulmonary angiogram and four positive lower-limb US scans. Reread or follow-up images depicted thromboembolic disease in 4.2% of patients. Nineteen patients (8%) with indeterminate final result were treated for thromboembolic disease with either anticoagulation or IVC filters. Reports on 22% of indeterminate studies contained recommendations for follow-up imaging, and those recommendations nonsignificantly increased the rate for those examinations from 13% to 19%. Review of discharge summaries showed 22% of studies are clinically interpreted as negative.

CONCLUSION

The two major causes of indeterminism are motion artifacts and poor contrast enhancement.

Suspected acute pulmonary embolism: evaluation with multi-detector row CT versus digital subtraction pulmonary arteriography

PURPOSE

To determine diagnostic accuracy of four-channel multi-detector row computed tomography (CT) in emergency room and inpatient populations suspected of having acute pulmonary embolism (PE) who prospectively underwent both CT and pulmonary arteriography (PA).

MATERIALS AND METHODS

Patients referred for PA to assess suspected PE were eligible. Institutional review board approval and written informed consent were obtained. All patients underwent CT and PA within a 48-hour period. For CT, 4 x 2.5-mm collimation was used. Three readers independently evaluated each study for PE presence. PE status, vessel level, and lobar location were determined by means of majority rule, and interobserver agreement (kappa) was calculated for PE status, as assessed with each modality. Sensitivity and specificity of CT were calculated by using PA as the reference standard. Two radiologists later reviewed false-positive CT studies.

RESULTS

The study group comprised 93 patients (median age, 56 years; range, 19-88 years). Sensitivity, specificity, and accuracy of CT were 100%, 89%, and 91%, respectively. kappa values were 0.71 and 0.83 for CT and PA, respectively, and were not significantly different between modalities. At PA, 18 patients (19%) had PE at 50 vessel levels (five main and/or interlobar, 24 segmental, and 21 subsegmental), 17 (94%) of which had PE at multiple sites. At CT, 26 patients (28%) had PE at 71 vessel levels (24 main and/or interlobar, 33 segmental, and 14 subsegmental). Twenty patients (77%) had PE at multiple sites. Review of eight false-positive CT studies showed an appearance highly suggestive of acute PE in three patients, chronic PE in one, and no PE in three; one study was inconclusive. CT better demonstrated large-level vessel involvement (P < .01), while PA better demonstrated small-level vessel involvement (P < .01).

CONCLUSION

Multi-detector row CT has an accuracy of 91% in the depiction of suspected acute PE when conventional PA is used as the reference standard.

Spiral computed tomography for acute pulmonary embolism

There is still considerable debate about the optimal diagnostic imaging modality for acute pulmonary embolism. If imaging is deemed necessary from an initial clinical evaluation such as d-dimer testing, options include nuclear medicine scanning, catheter pulmonary angiography, and spiral CT. In many institutions, spiral CT is becoming established as the first-line imaging test in daily clinical practice. With spiral CT, thrombus is directly visualized, and both mediastinal and parenchymal structures are evaluated, which may provide important alternative or additional diagnoses. However, limitations for the accurate diagnosis of small peripheral emboli, with a reported miss rate of up to 30% with single-slice spiral CT so far, have prevented the unanimous embrace of spiral CT as the new standard of reference for imaging pulmonary embolism. The clinical significance of the detection and treatment of isolated peripheral pulmonary emboli is uncertain. Evidence is accumulating that it is safe practice to withhold anticoagulation in patients with suspected pulmonary embolism on the basis of a negative spiral CT study. Remaining concerns about the accuracy of spiral CT for pulmonary embolism detection may be overcome by the introduction of multidetector-row spiral CT. This widely available technology has improved visualization of peripheral pulmonary arteries and detection of small emboli. The most recent generation of multidetector-row spiral CT scanners appears to outperform competing imaging modalities for the accurate detection of central and peripheral pulmonary embolism. In this review, we assess the current role and future potential of CT in the diagnostic algorithm of acute pulmonary embolism.

CT angiography for diagnosis of pulmonary embolism: state of the art

In daily clinical routine, computed tomography (CT) has practically become the first-line modality for imaging of pulmonary circulation in patients suspected of having pulmonary embolism (PE). However, limitations regarding accurate diagnosis of small peripheral emboli have so far prevented unanimous acceptance of CT as the reference standard for imaging of PE. The development of multi-detector row CT has led to improved visualization of peripheral pulmonary arteries and detection of small emboli. The finding of a small isolated clot at pulmonary CT angiography, however, may be increasingly difficult to correlate with results of other imaging modalities, and the clinical importance of such findings is uncertain. Therefore, the most realistic scenario to measure efficacy of pulmonary CT angiography when PE is suspected may be assessment of patient outcome. Meanwhile, the high negative predictive value of a normal pulmonary CT angiographic study and its association with beneficial patient outcome has been demonstrated. While the introduction of multi-detector row technology has improved CT diagnosis of PE, it has also challenged its users to develop strategies for optimized contrast material delivery, reduction of radiation dose, and management of large-volume data sets created at those examinations.

Imaging of acute pulmonary emboli

Pulmonary embolism (PE) is a significant cause of morbidity and mortality after surgical procedures. Early diagnosis and prompt, effective management of this condition present considerable clinical challenges to surgeons. Imaging studies form the mainstay of diagnosis of PE and include plain radiography, ventilation-perfusion scan, venography, echocardiography, catheter pulmonary angiogram, CT pulmonary angiogram, and MR pulmonary angiogram. Each imaging modality has a role in the diagnosis of PE.

The effect of helical computed tomography on diagnostic and treatment strategies in patients with suspected pulmonary embolism

BACKGROUND

Helical computed tomography (CT) has been proposed as a first-line test for the diagnosis of pulmonary embolism. How the test affects the diagnostic evaluation of patients with suspected pulmonary embolism is unknown.

METHODS

We examined a cohort of 360 patients evaluated for pulmonary embolism at a teaching hospital in the 4 years following the introduction of the helical CT scan. We collected patient demographic and clinical data to calculate the pretest likelihood of pulmonary embolism; we then read the test results and determined rates of further testing and treatment for pulmonary embolism.

RESULTS

After the helical CT scan became available, the number of patients referred for pulmonary embolism testing increased markedly from 170 to 624 total evaluations during 1997 to 2000 (P <0.01). This rise was due to increased use of the helical CT scan (9% to 83% of evaluations, P <0.01) as the use of ventilation-perfusion scanning (79% to 17%, P = 0.03) and pulmonary angiography (12% to <1%, P <0.01) fell. There was no change in the pre-test likelihood of disease over time, but the percentage of scans that were positive for pulmonary embolism rose (14% to 32%, P =0.02). Clinicians treated all patients who had a positive CT scan, but became less likely over time to order further testing for patients who had a negative scan (30% to 12%, P = 0.02).

CONCLUSION

At this academic medical center, introduction of the helical CT scan had a profound effect on the evaluation of pulmonary embolism, resulting in more frequent use of the CT scan, and more frequent diagnosis and treatment of pulmonary embolism, despite no change in the pretest probability of disease. Future studies should confirm our findings and determine whether increased detection of pulmonary emboli results in improved outcomes.

Spiral CT for pulmonary embolism: the paradigm has shifted

Computed tomography (CT) is rapidly becoming the first-line modality for imaging pulmonary embolism (PE). However, limitations for the accurate diagnosis of small peripheral emboli have prevented the unanimous embrace of CT as the new standard of reference for imaging PE, although the actual significance of isolated peripheral emboli is uncertain. At the same time, the high negative predictive value of CT pulmonary angiography for excluding clinically significant PE has been established. The introduction of multidetector-row spiral CT has greatly improved visualization of peripheral pulmonary arteries and detection of small emboli. Previous concerns regarding the use of spiral CT for the accurate diagnosis of peripheral pulmonary emboli should thus be overcome. Multidetector-row spiral CT has become a widely available and cost-effective technology and appears to have surpassed other imaging modalities for the accurate detection of central and peripheral PE. In this review, the authors assess the current role of spiral CT in the diagnostic algorithm of PE.