Font Size

Solitary Pulmonary Nodule (cont.)

Exams and Tests

Blood tests are not diagnostic. However, the following tests may indicate whether the SPN is benign or malignant:

Anemia (low levels of hemoglobin) or an elevated erythrocyte sedimentation rate (speed at which red blood cells settle in anticoagulated blood) may indicate an underlying cancer or an infectious disease.

Elevated levels of liver enzymes, alkaline phosphatase, or serum calcium may indicate that the SPN is cancerous and spreading or that cancer is spreading from other parts of the body to the lung.

Persons who have histoplasmosis or coccidioidomycosis may have high levels of immunoglobulin G and immunoglobulin M antibodies specific to these fungi.

A tuberculin skin test is a simple skin test used to help determine whether the SPN has been caused by the bacteria Mycobacterium tuberculosis. The test involves injecting the tuberculin antigen (a substance that triggers the immune system to produce cells [antibodies] that attack and try to destroy the antigen) into the skin and observing the body’s response. If the SPN has been caused by tuberculosis, the injection site swells and reddens.

Chest x-ray film

Because SPNs are first detected on chest x-ray films, ascertaining whether the nodule is in the lung or outside it is important. A chest x-ray film taken from a lateral (side) position, fluoroscopy, or CT scan may help confirm the location of the nodule.

Although nodules of 5 mm diameter are occasionally found on chest x-ray films, SPNs are often 8-10 mm in diameter.

The most important step is determining the possibility and risk of the SPN being malignant.

Patients who have an older chest x-ray film should show it to their health care provider for comparison. This is important because the growth rate of a nodule can be ascertained. The doubling time of most malignant SPNs is 1-6 months, and any nodule that grows more slowly or more rapidly is likely to be benign.

Chest x-rays films can provide information regarding size, shape, cavitation, growth rate, and calcification pattern. All of these features can help determine whether the lesion is benign or malignant. However, none of these features is entirely specific for lung cancer.

Radiologic characteristics that may help establish the diagnosis with reasonable certainty include (1) a benign pattern of calcification, (2) a growth rate that is either too slow or too fast to be lung cancer, (3) a specific shape or appearance of the nodule consistent with that of a benign lesion, and (4) unequivocal evidence of another benign disease process.

CT scan

CT scan is an invaluable aid in identifying features of the nodule and determining the likelihood of cancer. In addition to the features seen on a chest x-ray film, CT scan of the chest allows better assessment of the nodule. The advantages of CT scan over chest x-ray film include the following:
- Better resolution: Nodules as small as 3-4 mm can be detected. Features of the SPN are better visualized on CT scan, thereby aiding the diagnosis.
- Better localization: Nodules can be more accurately localized.
- Areas that are difficult to assess on chest x-ray film are visualized better on CT scan.
- CT scan provides more details of the internal structures and more readily shows calcifications.

If the CT scan demonstrates fat within the nodule, the lesion is benign. This is specific for a benign lesion (ie, hamartoma).

CT scan helps distinguish between a neoplastic abnormality and an infective abnormality.

Positron emission tomography

Malignant cells have a higher metabolic rate than normal cells and benign abnormalities; therefore, the glucose uptake of malignant cells is higher. Positron emission tomography (PET) involves using a radiolabeled substance to measure the metabolic activity of the abnormal cells. Malignant nodules absorb more of the substance than benign nodules and normal tissue and can be readily identified on the 3-dimensional, colored image.

PET scan is an accurate, noninvasive exam, but the procedure is expensive.

Single-photon emission computed tomography

Single-photon emission computed tomography (SPECT) imaging is performed using a radiolabeled substance, technetium Tc P829.

SPECT scans are less expensive than PET scans but have comparable sensitivity and specificity. However, the test has not been evaluated in a large number of persons. In addition, the SPECT scans are less sensitive for nodules smaller than 20 mm in diameter.

Biopsy (a sample of cells is removed for examination under a microscope): Different ways are used to collect biopsy samples from the airway or lung tissue where the SPN is located.

Bronchoscopy: This procedure is used for SPNs that are situated closer to the walls of the airways. A bronchoscope (a thin, flexible, lighted tube with a tiny camera at the end) is inserted through the mouth or nose and down the windpipe. From there, it can be inserted into the airways (bronchi) of the lungs. During bronchoscopy, the health care professional takes a biopsy sample from the SPN. If the lesion is not easily accessible on the airway wall or is smaller than 2 cm in diameter, a needle biopsy may be performed. This procedure is called a transbronchial needle aspiration (TBNA) biopsy.

Transthoracic needle aspiration (TTNA) biopsy: This type of biopsy is used if the lesion is not easily accessible on the airway wall or is smaller than 2 cm in diameter. If the SPN is on the periphery of the lung, a biopsy sample has to be taken with the help of a needle inserted through the chest wall and into the SPN. It is usually performed with CT guidance. With SPNs larger than 2 cm in diameter, the diagnostic accuracy is higher (90-95%). However, the accuracy decreases (60-80%) in nodules that are smaller than 2 cm in diameter.