Is There an Ideal Diagnostic Algorithm in Solitary Pulmonary Nodules?

In some cases CXR and CT may present features that suggest a benign disease, such as the presence of calcification (central, diffuse or popcorn patterns) in the context of the nodule or a low growth rate (stability over 2 years). A malignant nature may be suggested by the ‘corona radiata’ sign (fine linear strands extendindg 4–5 mm outward from the nodule) or the presence of stippled or eccentric calcification patterns [1, 4] . Magnetic resonance imaging (MRI) has a very limited role in the evaluation of SPNs, although it can be beneficial in patients who do not tolerate intravenous contrast [2] . Overall, conventional imaging often fails to provide conclusive information regarding the nature of an SPN, as many nodules are not calcified, and often there are no previous CXRs or CT scans to review for comparison. Positron emission tomography (PET) has become a commonly performed imaging modality in many human tumours, as the radiotracer most frequently used, [ 18 F]fluorodeoxyglucose ( 18 F-FDG), enters highly metabolic tumour cells revealing the sites of active disease. Since functional abnormalities may occur earlier than anatomical changes, PET imaging can contribute to a more accurate definition of areas of malignancies, even outside the thorax, therefore providing staging information on whole-body PET imaging. Moreover PET has a higher diagnostic accuracy than CT in detecting lymph nodal involvement [3] . False PET results may be due to lesion size smaller than the PET spatial resolution (about A solitary pulmonary nodule (SPN) is radiologically defined as a single lesion that is ! 3 cm in diameter, surrounded by lung parenchyma and without associated adenopathy or atelectasis [1, 2] . The distinction between SPNs and larger nodules, called masses, is based on their higher probability of malignancy, which requires a more aggressive approach with prompt resection usually advisable. Most SPNs are incidental findings at chest X-ray (CXR) or computed tomography (CT). Older studies showed that SPNs are evident in 1 of 500 CXRs, and the widespread use of CT and spiral CT has increased the detection rate of SPNs [2] . Although most SPNs are benign, the incidence of cancer in SPNs ranges from 10 to 70% [3] . The probability of malignancy is higher in heavy smokers with haemoptysis, higher age, larger nodule size or previous malignancy [4] . The differential diagnosis of an SPN includes neoplastic, inflammatory, vascular, traumatic and congenital lesions, and, less frequently, rheumatoid nodules, granulomas and sarcoidosis [1] . The main concern in a patient presenting with an SPN is to reach an accurate diagnosis of malignancy, since an early detection enables a better prognosis, while avoiding the morbidity and mortality associated with thoracotomy in those having a benign disease. Different diagnostic algorithms have been proposed for the SPN, but a standard clinical strategy has not been identified yet. Published online: June 23, 2006