Objective: The aim of this prospective study was to summarize all of the qualitative and quantitative imaging criteria for the differentiation of solitary pulmonary lesions (SPLs) as malignant (MSPLs) or benign (BSPLs) described in the literature and to critically analyze the different characteristics in order to evaluate their clinical importance and usefulness as criteria for a discrimination during the primary diagnostic assessment of SPLs using chest radiography, spiral computed tomography (SCT) and high-resolution computed tomography (HRCT).
Materials and methods: SPLs were examined, evaluated and then completely removed by surgery in 104 consecutive patients (MSPLs n=81, BSPLs n=23). No SPL was excluded by size. Chest radiography was performed with frontal and lateral views, SCT was carried out with a slice thickness of 8 mm and HRCT with a slice thickness of 1 mm and a 12-cm field of view.
Results: All the characteristics which enabled a reliable differentiation of MSPLs from BSPLs were characteristics which were observed significantly more frequently in MSPLs than BSPLs. Useful characteristics for the differentiation of MSPLs from BSPLs (1) using chest radiography were the indistinct edge (P<0.0001) and a ground-glass opacity of the lung parenchyma adjacent to the SPL (P<0. 05); (2) using SCT the presence of spicules (P<0.0005), the vessel sign (P<0.0005), necrotic areas (P<0.001), spicules extending to the visceral pleura (P<0.005), circumscribed pleural thickening (P<0. 005), inhomogeneity (P<0.01), a ground-glass opacity of the lung parenchyma adjacent to the SPL (P<0.01), the lesion density (P<0.05), pleural retraction (P<0.05) and the bronchus sign (P<0.05); and (3) using HRCT the presence of spicules (P<0.00005), spicules extending to the visceral pleura (P<0.0005), the vessel sign (P<0.0005), pleural retraction (P<0.001), circumscribed pleural thickening (P<0. 001), the bronchus sign (P<0.005), a ground-glass opacity of the lung parenchyma adjacent to the SPL (P<0.01), the lesion density (P<0.05) and the length of spicules (P<0.05). Using any one of the characteristics with a significance level of P<0.01, the identification of MSPLs (1) using chest radiography showed a sensitivity of 64.2% and a specificity of 82.6% (accuracy of 68.3%); (2) using SCT a sensitivity of 88.9% and a specificity of 60.9% (accuracy of 82.7%); and (3) using HRCT a sensitivity of 91.4% and a specificity of 56.5% (accuracy of 83.7%).
Conclusions: Using chest radiography, SCT and HRCT, a precise morphological assessment of the periphery of the pulmonary lesion and the adjacent visceral pleura is necessary to distinguish MSPLs from BSPLs. In this respect SCT and HRCT are useful in differentiation of MSPLs from BSPLs. However, metastases strongly resembled benign lesions in terms of size and edge type and chronic inflammatory pseudotumors as a group mimic MSPLs.