Dual Energy Computed Tomography Demonstrated Lung Ventilation/Perfusion Mismatch in a 19-Year–Old Patient With Pulmonary Embolism
A 19-year–old woman was transferred into our hospital because of left lower extremity swelling for 4 years, anasarca for 2 months, and abnormal urine tests for 3 weeks. The patient had sudden symptoms of cough and hemoptysis 4 years ago, and her chest plain film showed abnormal bilateral lung opacities. Tuberculosis was suspected, although no definitive tubercle bacilli was found. The patient had left lower extremity swelling and left chest pain 2 weeks after antituberculosis therapy. The above-mentioned symptoms resolved after anticoagulant therapy. One year ago, the patient began to present decreased platelet amount and mild anemia. Two months ago, the patient had left low extremity swelling aggravated and abnormal urine tests, including urine protein (++++) and occult blood (++). Routine blood test showed white blood cell of 3.3×109/L, hemoglobin of 85 g/L, platelet of 86×109/L. Blood biochemical tests showed albumin of 14.4 g/L, creatine level of 0.64 mg/dL, decreased C3 and C4 level, positive antinuclear antibody, and antidouble strand antinuclear antibody. Based on the clinical and laboratory findings, systemic lupus erythematosus was suspected and methylprednisolone plus therapy was initiated.
Routine d-dimer test was positive (0.67 mg/dL). Thus, screening of venous thromboembolism was initiated. Low-extremity compressed ultrasonography was performed and venous thrombus in the left common femoral vein was found. Then, the patient was recommended to screen pulmonary embolism and renal vein thrombosis. Renal computed tomography (CT) venography was performed in a dual-source CT scanner (Somatom Deinition, Siemens Medical System) and showed that bilateral renal vein and inferior vena cava were negative. Dual energy CT ventilation and perfusion imaging in the dual-source CT scanner (Somatom Deinition, Siemens Medical System) were performed. Xenon-enhanced dual-energy CT ventilation imaging showed normal xenon distribution (Figure 1) in both lungs 80 seconds after inhaling the mix gas with 30% xenon 70% oxygen. Five minutes after xenon-enhanced dual-energy CT scan, iodinated contrast-enhanced dual-energy CT perfusion imaging was performed and showed left pulmonary artery occlusion (Figure 2) at CT pulmonary angiography from average weighted virtual 120-kVp images and corresponding perfusion defect in the whole left lung (Figure 3) at iodine maps. Ventilation/perfusion mismatch, a typical finding of pulmonary embolism in ventilation/perfusion scintigraphy, was clearly visualized at dual-energy CT perfusion and ventilation images (Figures 1 through 3). The patient did not undergo kidney biopsy because of venous thromboembolism events. She received anticoagulant therapy with low-molecular-weight heparin injected subcutaneously 2 times a day for 1 week. The patient was discharged after her symptoms resolved.
The introduction of recent CT scanner generations enables dual-energy CT applications in routine practice. Dual-energy CT pulmonary angiography can simultaneously provide lung perfusion and pulmonary vessel mapping, affording more options for comprehensive lung imaging, and ordinarily does not expose patients to any significant additional radiation over that of standard CT pulmonary angiography techniques.1 Previously, many studies have demonstrated the clinical value of dual energy CT perfusion and ventilation imaging,1–4 for example, iodinated contrast-enhanced dual-energy CT has been used to investigate the iodine distribution in the lungs, improving the detection of pulmonary embolism,1,2 whereas xenon-enhanced dual-energy CT has been used to map the xenon distribution in the lungs, which is helpful to visualize ventilation status in patients with emphysema and asthma and to assess the collateral ventilation of bronchus atresia in a static or dynamic scan.3,4 Both xenon-enhanced dual-energy CT and iodinated contrast-enhanced dual-energy CT can be simultaneously performed to show both regional lung ventilation and perfusion function.5 This case is the first report to demonstrate the feasibility of perfusion/ventilation mismatch in 1 patient with pulmonary embolism visualized on CT, to the best of our knowledge.
- © 2012 American Heart Association, Inc.