Abstract and Introduction
The widespread utilization of chest CT scans has increased the importance of the proper evaluation of incidentally found lung nodules. The primary goal in the evaluation of these nodules is to determine whether they are malignant or benign. Clinical factors such as older age, tobacco smoking, and current or remote history of malignancy increase the pretest likelihood of malignancy. Radiological features of these nodules are important in differentiating benign from malignant lesions. However, the etiology of the lung nodules frequently remains indeterminate and requires further evaluation. The approach to the management of indeterminate lung nodules ranges between observation with repeat chest CT scan, further diagnostic studies such as PET scan or invasive procedures to obtain tissue diagnosis. This article reviews the importance of the different radiological features of lung nodules. This is followed by an update on the approach to the management of the different types of small lung nodules.
With the widespread use of radiographic modalities, such as chest radiographs and computer tomography (CT) of the chest, in the evaluation of a wide variety of patient complaints an ever-increasing number of lung parenchymal abnormalities are being detected. This article will focus on the specific finding of small pulmonary nodules. A pulmonary nodule is a lung parenchymal abnormality measuring 1–30 mm in size, surrounded by normal lung parenchyma and not associated with adenopathy or atelectasis. Any density measuring more than 30 mm is considered a mass and must be presumed malignant until proven otherwise.
Pulmonary nodules are detected in 0.2% of chest radiographs and 8–51% of CT scans in screening trials.[2–4] The reported incidence of solitary pulmonary nodules appears to be 150,000 nodules annually in the USA with over 90% of these being incidental. Chest CT is the best imaging technique to identify the origin and location of the nodule as 20% of 'nodules' found on chest x-ray turn out to be nonpulmonary when imaged with another technique.[5–7] These entities include nipple shadows, skin lesion, rib fractures, blood vessel end, confluence of shadows or ECG lead.
This article discusses the diagnostic approach to pulmonary nodules, and the clinical and radiological characteristics of benign versus malignant nodules. Lung cancer is the primary etiology of malignant nodules and is the most common cause of cancer-related death in both sexes. There has not been much progress in the overall 5-year survival rates in patients with lung cancer and survival remains rather low at 15%. However, an early-detected lung cancer, namely stage IA (T1, N0, M0) that is treated with resection may portend a long-term survival of 80% or better.[8–10] Therefore, it is of utmost importance to identify and treat pulmonary nodules that are strongly suspicious for malignancy.
The majority of studies indicate the range of malignancy to be 1.1–12% with a wide range between studies.[2,6,11] Adenocarcinoma is the most likely type of lung cancer identified in lung nodules, whereas small-cell carcinoma is rarely an etiology of malignant lung nodules.[12–13] Carcinoid tumors account for approximately 1–5% of malignant nodules. The etiology of benign lung nodules varies, with infectious granulomas, round pneumonias and abscesses accounting for approximately 70–80% of the cases.[5,12–13] Benign tumors are rare with a reported incidence of 10%, with hamartoma accounting for the majority of these.[13–14] The different causes of pulmonary nodules are outlined in Table 1.
Future Oncol. 2013;9(6):855-865. © 2013 Future Medicine Ltd.