Solitary pulmonary nodule (SPN) is typically defined as an intra -parenchymal focal, round or oval area of increased opacity <3 cm in diameter.12 Nearly 1 in every 500 chest radiographs taken reveals a newly diagnosed SPN. More than 150,000 SPNs are detected annually in the United States alone.3 This estimate is mainly based on chest radiographs. Now, with increasing use of computed tomography (CT) of the chest for screening of lung cancer and chest CT angiography (CTA) for diagnosing pulmonary embolus and for cardiac evaluation, this number is rapidly increasing.
Data on the use of CT screening in smokers from the Early Lung Cancer Action Project showed noncalcified nodules in 233 out of 1000 participants.4 The Mayo Clinic study found 2244 non-calcified nodules in 1000 of 1520 participants.5 It is important to note that although overall survival in lung cancer is poor, patients with stage IA (Tl NO M0) cancer have a reported 5-year survival of 61% to 85%,6 and, thus, early resection of a malignant nodule can make a large difference in patient outcome. However, with <30% of SPNs representing a primary or metastatic malignancy, determining the appropriate course of action is a challenge.
Growth rate assessment is a good differentiating factor between a benign and malignant process, but given that the typical doubling time of a malignant nodule is between 30 and 400 days, most commonly proposed follow-up protocols are at 3-month intervals for up to 1 year, and then every 6 months for another year. Some people advocate considering an even longer follow-up.7 Many patients, however, believe that waiting 3 months, not to mention up to 2 years, without at least a preliminary diagnosis is an unacceptable option. Additionally, stability over a short interval cannot exclude malignancy, yet delay can worsen the prognosis (Figure 1).
Evaluation of growth in a small nodule is often quite imprecise as well. Morphologic characteristics of an SPN are often helpful in determining its etiology. Thin-section CT can improve detection of calcification within an SPN. However, the majority of pulmonary nodules will still remain indeterminate following thin-section CT imaging. It has also been shown that despite all the accumulated data on morphologic characteristics of benign and malignant nodules, simple Bayesian analysis of patient characteristics and selected radiologic features is superior to evaluation by experienced radiologists in the stratification of benign and malignant nodules.8
Surgical resection of the nodule is definitely diagnostic and may be curative. However, the morbidity and the expense associated with resection of every incidentally found nodule make this approach simply impractical. Biopsy has not been proven to be a viable option either. Transthoracic needle aspiration yields a positive tissue diagnosis in approximately 60% of lesions <2 cm,9 with pneumothorax rates as high as 64.2%.10 Bronchoscopy has a lower complication rate, yet its diagnostic yield for nodules <2 cm is approximatedly 10% and is only 40% to 60% for nodules 2 to 4 cm in diameter (Figure 2).7 Use of contrast enhancement with CT is reported to have high sensitivity (98%) for malignant nodules; however, specificity and overall accuracy are much lower.
The problem facing a clinician is even greater if >1 nodule is present, which is not that uncommon, especially after a CT of a patient initially presenting with an SPN on chest radiography. Granulomatous disease, lung cancer with metastases, and metastases from a remote primary cancer all can present with multiple nodules. In patients without known malignancy, there is no clear algorithm to follow, especially since resection of all of the nodules is quite impractical. A different problem along the same lines is an SPN in a patient with a recent or remote history of malignancy, but without known metastatic disease (Figures 3 through 5).