Can Malignant and Benign Pulmonary Nodules Be Differentiated With DWI?
Can Malignant and Benign Pulmonary Nodules Be Differentiated With DWI?
Objective: The objective of our study was to evaluate whether diffusion-weighted imaging (DWI) with a high b factor can be used to differentiate malignancies from benign pulmonary nodules.
Materials and Methods: This study included 54 pulmonary nodules (≥ 5 mm in diameter) in 51 consecutive patients (37 men, 14 women; mean age, 65.7 years; age range, 31-88 years). Thirty-six (67%) of the 54 pulmonary nodules were malignant, and 18 (33%) were benign. Two radiologists independently reviewed the signal intensity of the nodules on DWI with a b factor of 1,000 s/mm using a 5-point rank scale without knowledge of clinical data. This scale was based on the following scores: 1, nearly no signal intensity; 2, signal intensity between 1 and 3; 3, signal intensity almost equal to that of the thoracic spinal cord; 4, higher signal intensity than that of the spinal cord; and 5, much higher signal intensity than that of the spinal cord. The Mann-Whitney U test and the receiver operating characteristic (ROC) curve were used to calculate the difference between the scores of malignant and benign nodules.
Results: On DWI, the mean score of malignant pulmonary nodules (4.03 ± 1.16 [SD]) was significantly higher (p < 0.01) than that of benign nodules (2.50 ± 1.47), with an area under the ROC curve of 0.796 (95% CI, 0.665-0.927). When a score of 3 was considered as a threshold, the sensitivity, specificity, and accuracy were 88.9% (95% CI, 78.6-99.2%), 61.1% (38.6-83.6%), and 79.6% (68.9-90.3%), respectively. Three small metastatic nodules (13, 16, and 20 mm) and one bronchioloalveolar carcinoma scored 1 or 2 on the 5-point rank scale. Three granulomas, two active inflammatory lung nodules, and one fibrous nodule scored 4 or 5.
Conclusion: The signal intensity of pulmonary nodules may be useful for malignant and benign differentiation on DWI. However, the interpretation of small metastatic nodules, nonsolid adenocarcinoma, some granulomas, and active inflammatory nodules should be approached with caution.
A solitary pulmonary nodule is a common finding on chest radiography. PET with F-FDG and CT are two common noninvasive methods used to examine solitary pulmonary nodules. FDG PET, which is based on the metabolic uptake of FDG, has been reported to increase the diagnostic accuracy of benign and malignant nodule differentiation. However, because FDG PET shows an increased uptake in lung tissues with active inflammation or benign nodules, interpretation should be approached with caution.
Morphologic analysis based on the assessment of size, shape, and internal characteristics using CT has been the mainstay in evaluating pulmonary nodules. A nodule having a corona radiata appearance is likely to be malignant, whereas the presence of intranodular fat is a reliable indicator of a hamartoma. In general, the smaller the nodule, the more likely it is to be benign, especially nodules less than 5 mm in diameter. Findings of both calcification and lack of growth for at least 2 years are generally accepted as reliable signs of a benign nodule, but other findings have not proven useful for malignant and benign differentiation. The evaluation of tumor vascularity using contrast-enhanced CT has proven to be useful for distinguishing malignant nodules from benign nodules. In particular, the absence of significant lung nodule enhancement on CT is strongly predictive of benignancy. However, when the nodules had significant enhancement, some overlap was found especially between active granulomas or hypervascular benign tumors and malignant nodules.
Although MRI is used relatively infrequently because of its comparatively high cost, it has an inherent advantage in terms of tissue characterization. Indeed, some investigators have tried to discriminate malignancy from benign lung tumors by measuring their relaxation times, although the results have not been satisfactory because of a significant overlap of values. Tissue contrast attained using diffusion-weighted imaging (DWI) is different from that attained using conventional MR sequences. The diffusion technique reflects the diffusion motion of water protons in the tissues, producing different contrast in different kinds of tissues. Promising results have been achieved using this technique for differentiation between malignant and benign nodules in the liver, bone marrow, and head and neck. However, to our knowledge, there have been no reports about DWI applied to pulmonary nodules for differentiating malignancy from benignancy because the images in this area are likely to have susceptibility artifacts.
Takahara et al. introduced a new technique of DWI using a STIR sequence with a high b factor and free breathing with 10 excitations and concluded that this technique allows screening for malignancies in the entire body. Their results showed that a free-breathing technique with 10 excitations and STIR produced a higher contrast-to-noise ratio and good fat suppression compared with a breath-hold technique with 2 excitations and a chemical shift-selective pulse. The purpose of our study was to perform DWI of pulmonary nodules and evaluate whether DWI can be used to differentiate malignant from benign nodules and to analyze pulmonary nodules that are difficult to characterize as benign or malignant.
Objective: The objective of our study was to evaluate whether diffusion-weighted imaging (DWI) with a high b factor can be used to differentiate malignancies from benign pulmonary nodules.
Materials and Methods: This study included 54 pulmonary nodules (≥ 5 mm in diameter) in 51 consecutive patients (37 men, 14 women; mean age, 65.7 years; age range, 31-88 years). Thirty-six (67%) of the 54 pulmonary nodules were malignant, and 18 (33%) were benign. Two radiologists independently reviewed the signal intensity of the nodules on DWI with a b factor of 1,000 s/mm using a 5-point rank scale without knowledge of clinical data. This scale was based on the following scores: 1, nearly no signal intensity; 2, signal intensity between 1 and 3; 3, signal intensity almost equal to that of the thoracic spinal cord; 4, higher signal intensity than that of the spinal cord; and 5, much higher signal intensity than that of the spinal cord. The Mann-Whitney U test and the receiver operating characteristic (ROC) curve were used to calculate the difference between the scores of malignant and benign nodules.
Results: On DWI, the mean score of malignant pulmonary nodules (4.03 ± 1.16 [SD]) was significantly higher (p < 0.01) than that of benign nodules (2.50 ± 1.47), with an area under the ROC curve of 0.796 (95% CI, 0.665-0.927). When a score of 3 was considered as a threshold, the sensitivity, specificity, and accuracy were 88.9% (95% CI, 78.6-99.2%), 61.1% (38.6-83.6%), and 79.6% (68.9-90.3%), respectively. Three small metastatic nodules (13, 16, and 20 mm) and one bronchioloalveolar carcinoma scored 1 or 2 on the 5-point rank scale. Three granulomas, two active inflammatory lung nodules, and one fibrous nodule scored 4 or 5.
Conclusion: The signal intensity of pulmonary nodules may be useful for malignant and benign differentiation on DWI. However, the interpretation of small metastatic nodules, nonsolid adenocarcinoma, some granulomas, and active inflammatory nodules should be approached with caution.
A solitary pulmonary nodule is a common finding on chest radiography. PET with F-FDG and CT are two common noninvasive methods used to examine solitary pulmonary nodules. FDG PET, which is based on the metabolic uptake of FDG, has been reported to increase the diagnostic accuracy of benign and malignant nodule differentiation. However, because FDG PET shows an increased uptake in lung tissues with active inflammation or benign nodules, interpretation should be approached with caution.
Morphologic analysis based on the assessment of size, shape, and internal characteristics using CT has been the mainstay in evaluating pulmonary nodules. A nodule having a corona radiata appearance is likely to be malignant, whereas the presence of intranodular fat is a reliable indicator of a hamartoma. In general, the smaller the nodule, the more likely it is to be benign, especially nodules less than 5 mm in diameter. Findings of both calcification and lack of growth for at least 2 years are generally accepted as reliable signs of a benign nodule, but other findings have not proven useful for malignant and benign differentiation. The evaluation of tumor vascularity using contrast-enhanced CT has proven to be useful for distinguishing malignant nodules from benign nodules. In particular, the absence of significant lung nodule enhancement on CT is strongly predictive of benignancy. However, when the nodules had significant enhancement, some overlap was found especially between active granulomas or hypervascular benign tumors and malignant nodules.
Although MRI is used relatively infrequently because of its comparatively high cost, it has an inherent advantage in terms of tissue characterization. Indeed, some investigators have tried to discriminate malignancy from benign lung tumors by measuring their relaxation times, although the results have not been satisfactory because of a significant overlap of values. Tissue contrast attained using diffusion-weighted imaging (DWI) is different from that attained using conventional MR sequences. The diffusion technique reflects the diffusion motion of water protons in the tissues, producing different contrast in different kinds of tissues. Promising results have been achieved using this technique for differentiation between malignant and benign nodules in the liver, bone marrow, and head and neck. However, to our knowledge, there have been no reports about DWI applied to pulmonary nodules for differentiating malignancy from benignancy because the images in this area are likely to have susceptibility artifacts.
Takahara et al. introduced a new technique of DWI using a STIR sequence with a high b factor and free breathing with 10 excitations and concluded that this technique allows screening for malignancies in the entire body. Their results showed that a free-breathing technique with 10 excitations and STIR produced a higher contrast-to-noise ratio and good fat suppression compared with a breath-hold technique with 2 excitations and a chemical shift-selective pulse. The purpose of our study was to perform DWI of pulmonary nodules and evaluate whether DWI can be used to differentiate malignant from benign nodules and to analyze pulmonary nodules that are difficult to characterize as benign or malignant.