Solitary Pulmonary Nodules

by Marnix Verhofste, MD

Solitary pulmonary nodules are defined as a circular opacity less than 3 cm. There are about 150,000 cases per year in the U.S. The most sensitive way to diagnose these is a spiral CT.  If there is no radiological change over two years, a nodule is considered benign.

There are about 80 distinct clinical entities that can present as a solitary pulmonary nodule. More than half of them require disease specific therapy. Malignancy rates are anywhere from 10-70% in the literature. Most benign lesions have central laminated calcifications and some malignancies can present with eccentric and stippled calcifications.

Sometimes it is very difficult to differentiate radiologically infectious disease with caner.  TB can some times present as a speculated lesion, as can fungi. Often PET scans can be false positive in the case of infectious diseases.

Sarcoidosis can be difficult to differentiate with caner. Diagnosis of sarcoidosis is performed by cervical mediastinoscopy. Benign nodules as hamartoma and hemangioma can be relatively easily identified on CT scan.  Fine needle aspiration of a hamartoma will demonstrate the diagnosis. Fine needle aspiration of a hemangioma can cause serious bleeding.

The most common malignant nodules are adenocarcinoma and squamous cell carcinoma. The earlier these can be diagnosed, especially in high risk groups, the earlier stage they are and the better the survival.  High-risk groups are smokers, especially age 50 or older, and if there are signs of hemoptysis and if these nodules are not calcified.

Very important in the workup is the cancer doubling time. There is usually about three to four months, so CT scans should be repeated in two to four months. If there is no change over two years, a CT scan can be considered diagnostic for benign disease. Cavitation is typical for an abscess but is not unusual for large squamous cell carcinomas.

Other malignant nodules are carcinoids. A carcinoid has an excellent prognosis if it is typical and if surgery is performed such as lobectomy.  Carcinoids are not sensitive to radiation or chemotherapy.

Other causes of malignant nodules are colorectal, breast, head and neck carcinoma, sarcoma, melanoma, and renal cell carcinoma. All of these are forms of resectable metastases in the lung.

PET scans are an important tool in the diagnostic workup of a solitary pulmonary nodule.  It is very sensitive but not specific. If a PET scan is positive, it is an indication that we should investigate this area. PET scans are commonly positive in infections and inflammations. False negative PET scans have been seen frequently in carcinoids and bronchoalveolar carcinoma.  If a nodule is less than 1 cm, the performance of a pet scan is very weak.

A fairly accurate way of diagnosing a solitary pulmonary nodule is fine needle aspiration. The radiologist does this under CT scan guidance.  There is a significant risk for pneumothorax , anywhere from 5-60%, but most pneumothoraces can be treated without a chest tube. It can also cause bleeding and hemoptysis.  It is not indicated if the patient has severe emphysema, coagulopathies, is unable to lie still and in pneumonectomy patients.

It is also not unusual to have non-specific results especially if there is an area of pneumonia around the nodule and the needle aspiration missed the tumor center of the nodule. Results will be false negative then.  There is also a very low sensitivity for lymphoma because not enough tissue can be obtained for subtyping. 

Bronchoscopy is a complementary diagnostic tool for peripheral nodules and has a low yield.

Screening in the past has not been shown to be beneficial by means of chest x-ray and sputum examination. CT scans should be done periodically on people with solitary pulmonary nodules over a period of two years. Aggressive diagnostic workup should be done if a lesion is suspicious on CT scan, needle biopsy, and/or thoracoscopy.  This should always be entertained in high risk populations like smokers over age 40.

More recent reports have shown a higher than previously expected incidence of carcinoma in small nodules. Recent reports have also shown the benefits of CT screening in high-risk populations.

Thoracoscopy has a very low morbidity and mortality. The worst mistake is to follow a malignant solitary pulmonary nodule and resect at a later more advanced stage. This would cause significantly lower survival. The five-year survival rate for a stage Ia lung cancer is 75%, while for a stage IV it is in the single digits.