Rationale and Objectives
Most fluorine-18 fluorodeoxyglucose (FDG)-positron emission tomography with computed tomography (PET/CT) studies are performed on cancer patients. These patients are at increased risk of pulmonary embolism (PE). In this retrospective review, we determined the rate of PE, and the prevalence of associated FDG-PET findings on intravenous (IV) contrast-enhanced PET/CT.
Materials and Methods
We identified all PET/CT studies performed at our institution with a reported finding of PE between January 2005 and October 2012. The medical record was reviewed for symptoms, which were identified after the diagnosis of PE, and whether the patients received treatment. The prevalence of associated FDG-PET findings was determined.
Results
A total of 65 total cases of PE (of 182,72 total PET/CT examinations) were identified of which 59 were previously unknown. This gives an incidental PE (IPE) rate of 0.32%. Of the patients where sufficient clinical information was available, 34 of 36 (94%) were treated either with therapeutic anticoagulation or inferior vena cava filter, and 30 of 36 (83%) were asymptomatic in retrospect. Of the patients with IPE, we found nine (15.2%) with associated focal pulmonary artery hypermetabolism, three (5.1%) with hypermetabolic pulmonary infarction, and one with increased isolated right ventricular FDG uptake (1.7%). One case of chronic PE demonstrated a focal hypometabolic filling defect in a pulmonary artery on PET.
Conclusions
We found IPE in 0.32% of PET/CT scans. Focal pulmonary artery hypermetabolism or hypometabolism, and hypermetabolic pulmonary artery infarction with the “rim sign” were uncommonly associated with PE. These findings could raise the possibility of IPE in non-IV contrast-enhanced PET/CT studies.
Acute pulmonary embolism (PE) represents a potential life threatening complication of venous thrombosis and is notoriously variable in presentation. Oncology patients have a higher risk of PE and often present without the typical clinical manifestations . These so-called asymptomatic PEs are clinically significant in oncology patients. They serve as a marker for future symptomatic venous thromboembolism (VTE), a term that encompasses both deep venous thrombosis (DVT) and PE , and are associated with decreased survival . The current consensus is for therapeutic intervention in these patients despite the absence of symptoms .
Several previous studies have investigated the rates of incidental PE (IPE) on contrast-enhanced computed tomography (CT) studies in the oncologic population, with reported rates ranging from 0.58% to 4.0% . Since its approval by the Food and Drug Administration in 2000, fluorine-18 fluorodeoxyglucose (FDG)-positron emission tomography fused with concurrent computed tomography (PET/CT) has rapidly evolved into a cornerstone imaging modality in oncology. At our institution, approximately 95% of PET/CT studies are performed in patients with known or suspected malignancy, and the routine imaging protocol includes intravenous (IV) contrast. In general, most centers perform low-dose, noncontrast-enhanced CT as part of their routine FDG-PET/CT protocol. At our institution, there is a consensus between referring clinicians and the radiology department that patients undergoing PET/CT have a contrast-enhanced diagnostic quality CT unless there is a contraindication such as renal failure or contrast allergy. One previous study found IPE in 13 of 2216 patients (0.59%) who had a contrast-enhanced PET/CT . The aim of our study was to evaluate the incidence of IPE in patients referred for FDG-PET/CT studies in a much larger cohort. An additional goal was to identify and characterize associated PET findings and their relative frequency.
Materials and methods
Patient Selection
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Scan Technique
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Imaging and Chart Review
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Results
Total Number of Cases Reviewed
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Incidence of PE
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Table 1
Pulmonary Embolism Characteristics
Total IV contrast-enhanced PET/CT scans ∗ 18,272 Number of cases with PE 65 Number of cases of incidental PE 59 (0.32%) Number of cases with chronic PE 6 Location in pulmonary artery Main PA 9/59 (15%) Lobar PA 15/59 (25%) Segmental PA 27/59 (46%) Subsegmental PA 8/59 (14%)
IV, intravenous; PA, pulmonary artery; PE, pulmonary embolism; PET/CT, positron emission tomography with computed tomography.
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Table 2
Demographics of Patients with IPE
Age Mean 55.8 Standard deviation 15 Range 23–84 Malignant neoplasm ∗ 57/59 (97%) Metastases 34/51 (67%) Female 30/59 (51%) Male 29/59 (49%) Treatment † Chemotherapy 30/47 (64%) Surgery 13/47 (28%) Radiation 7/47 (15%) None 19/47 (21%)
IPE, incidental pulmonary embolism.
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Table 3
Characteristics of Tumors
Type # IPE Total ∗ Incidence ∗ Breast 13 2563 0.51% Melanoma 10 2839 0.35% Lymphoma 6 Lung 5 Esophageal 4 Colon 3 Anorectal 2 Ewing’s sarcoma 2 Multiple myeloma 2 Other 10 No malignancy 2
IPE, incidental pulmonary embolism.
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Pulmonary Emboli Characteristics
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Clinical Symptoms and Treatment with Anticoagulation
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Review of Associated FDG-PET Findings
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Table 4
PET Findings Associated with IPE
High SUV in right ventricle 1/59 (2%) Hypermetabolic pulmonary infarction 3/59 (5%) Hypermetabolic pulmonary artery 9/59 (15%) Mean SUV 2.2 ± 0.7 Max SUV 3.2 Main PA 1/9 Lobar PA 2/9 Segmental PA 4/9 Subsegmental PA 2/9
IPE, incidental pulmonary embolism; PA, pulmonary artery; SUV, standardized uptake value.
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Discussion
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Conclusions
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Supplementary Data
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Supplemental Figures1–4
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