Solitary pulmonary nodulehttp://www.radiologyassistant.nl/en/460f9fcd50637 The Radiology Assistant Solitary pulmonary nodule: benign versus malignant Differentiation with CT and PET-CT Ann Leung and Robin Smithuis Department of Radiology, Stanford University Medical Center, Stanford, California and the Department of Radiology, Rijnland Hospital, Leiderdorp, the Netherlands CT: benign versus malignant Calcification Size Growth Shape Margin Air Bronchogram sign Solid and Ground-glass components Contrast enhancement PET-CT: benign versus malignant Conclusion Publicationdate:20-5-2007 The differential diagnosis of a solitary pulmonary nodule is broad and management depends on whether the lesion is benign or malignant. In this overview we will discuss some of the new features that can help to differentiate between benign and malignant nodules based upon CT and PET-CT findings. CT: benign versus malignant Calcification Diffuse, central, laminated or popcorn calcifications are benign patterns of calcification. These types of calcification are seen in granulomatous disease and hamartomas. All other patterns of calcification should not be regarded as a sign of benignity. Benign pattern of calcification The exception to the rule above is when patients are known to have a primary tumor. For instance the diffuse calcification pattern can be seen in patients with osteosarcoma or chondrosarcoma. Similarly the central and popcorn pattern can be seen in patients with GI-tumors and patients who previously had chemotherapy. Size A solitary pulmonary nodule (SPN) is defined as a single intraparenchymal lesion less than 3 cm in size and not associated with atelectasis or lymphadenopathy. A lesion greater than 3 cm in diameter is called a mass. This distinction is made, because lesions greater than 3 cm are usually malignant, while smaller lesions can be either benign or malignant. Relationship between SPN-size and chance of malignancy in patients with high risk for lung cancer Swensen et al studied the relationship between the size of a SPN and the chance of malignancy in a cohort at high risk for lung cancer (1). Their findings are listed in the table on the left. They concluded that benign nodule detection rate is high, especially if lesions are small. Of the over 2000 nodules that were less than 4 mm in size, none was malignant. 1 of 4 09-Jun-11 4:25 PM since stability over 2 years is highly associated with benignity.Solitary pulmonary nodule http://www. Shape Japanese screening studies showed that a polygonal shape and a three-dimensional ratio > 1.highly associated with malignancy (figure) Lobulated or scalloped margins . which is a benign sign.more likely benign unless metastatic in origin Corona radiata sign in a malignant lesion with spiculation at the margin. The case on the left shows an airbronchogram seen as a linear lucency (broad arrow) and as a more cystic lucency (small arrow) due to the fact that the bronchus is seen en face. Air Bronchogram sign Recent studies have showed that an air bronchogram is more commonly seen in malignant pulmonary nodules. The three-dimensional ratio is measured by obtaining the maximal transverse dimension and dividing it by the maximal vertical dimension. A peripheral subpleural location was also a sign of benignity in this study. A polygonal shape means that the lesion has multiple facets (multi-sided). Transverse image (left) and coronal reconstruction (right) Three-dimensional ratio = transverse dimension : vertical dimension Margin Corona radiata sign .nl/en/460f9fcd50637 Growth Comparison with prior imaging studies is often the most useful procedure to determine the importance of the finding of a SPN.3).intermediate probability Smooth margins . It is most commonly seen in BAC (bronchoalveolar cell carcinoma) and adenocarcinoma.radiologyassistant.78 was a sign of benignity (2. Air bronchogram sign seen in 2 of 4 09-Jun-11 4:25 PM . A large three-dimensional ratio indicates that the lesion is relatively flat. 2. It is however homogeneous in attenuation. 4 consecutive scans at 1 minute interval are performed. After a baseline scan. Nonsolid .nl/en/460f9fcd50637 On the left two solitary pulmonary nodules.radiologyassistant. It proved to be an adenocarninoma. 3. Nodule > 5mm Relatively spherical Homogeneous. This applies only for nodules with the following selection criteria: Baseline scan and scans after contrast enhancement. The lucencies and frank air bronchograms should not mislead you in thinking that it probably is infection.only ground-glass lesions had a malignancy rate of 18%. LEFT: 1 in 5 malignant RIGHT: 2 in 3 malignant Contrast enhancement Contrast enhancement less than 15 HU has a very high predictive value for benignity (99%). fat or calcification No motion or beam hardening artifacts 3 of 4 09-Jun-11 4:25 PM . while the other one was a fungal infection. Based upon the morphology. 1. Benign lesion with < 15 HU enhancement. Partly solid nodule containing ground-glass component most likely to be malignant On the far left a lesion that only has a ground-glass appearance and next to it a lesion that has both ground-glass and solid components.Solitary pulmonary nodule http://www. The lesion next to it is lobulated in contour and has some spicules radiating to the pleura. which lesion has the most malignant features? The lesion on the far left has a spicuated margin and has lucencies within it. 4. no necrosis. Solid and Ground-glass components Another result from screening studies is that nodules containing a ground-glass component are more likely to be malignant (5). Partly solid lesions with ground-glass components had a malignancy rate of 63%. Only solid lesions had a malignancy rate of only 7%. Based on these findings we should be most concerned that the lesion on the far left is malignant. The likelihood of malignancy is 1:5 for the lesion on the far left and 2:3 for the lesion with both ground-glass and solid components. 180:1255-1263 3. 178:1053-1057 4 of 4 09-Jun-11 4:25 PM . When you perform PET-CT. AJR 2003. PET is usually false negative in size < 10 mm and low-grade malignancy including bronchoalveolar carcinoma and carcinoid With these specificity numbers. AJR 2003. PET is false positive in granulomatous disease 3.235:259-265. Small Solitary Pulmonary Nodules (1 cm) Detected at Population-Based CT Screening for Lung Cancer: Reliable High-Resolution CT Features of Benign Lesions Shodayu Takashima et al.nl/en/460f9fcd50637 PET-CT: benign versus malignant PET-CT plays an increasingly important role in the evaluation of solitary nodules. there will be false positives in about 20%. we have to be aware of the accuracy of PET-CT and we should have an idea about the prevalence of infectious and non-infectious granulomatous disease in the area that we practice. 180:955-964 4. With the increasingly important role of PET-CT. Conclusion In the differentiation of benign versus malignant solitary pulmonary nodules nowadays new imaging features have to be added. so it is a false negative PET.radiologyassistant. air bronchograms or cavities and the three-dimensional ratios of a lesion. Activity is not sufficient for the diagnosis malignancy. 2. you have to realize the following: 1. Indeterminate Solitary Pulmonary Nodules Revealed at Population-Based CT Screening of the Lung: Using First Follow-Up Diagnostic CT to Differentiate Benign and Malignant Lesions Shodayu Takashima et al. PET has a very high sensitivity 95%. CT Screening for Lung Cancer: Five-year Prospective Experience Stephen J. CT Screening for Lung Cancer Frequency and Significance of Part-Solid and Nonsolid Nodules Claudia I. We especially have to look for the presence of areas of ground-glass opacity. that was not hypermetabolic on the PET. On the left a patient with an adenocarcinoma. References 1. depending on the background prevalence of granulomatous disease. Swensen et al Radiology 2005.Solitary pulmonary nodule http://www. but a lesser specificity of only 81% 2. Henschke et al AJR 2002. False negative PET in a patient with adenocarcinoma.