Solitary Pulmonary Nodule (cont.)
- Because solitary pulmonary nodules 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, solitary pulmonary nodules are often 8-10 mm in diameter.
- The most important step is determining the possibility and risk of the
solitary pulmonary nodule being malignant.
- Patients who have an older chest
X-ray film should show it to their health care professional for comparison. This is important because the growth rate of a nodule can be ascertained. The doubling time of most malignant
solitary pulmonary nodules is 1 to 6 months, and any nodule that grows more slowly or more rapidly is likely to be benign.
X-ray 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
(round smooth borders, cancers may have a so-called stellate [star shaped]
pattern), and (4) unequivocal evidence of another benign disease process.
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
solitary pulmonary nodule 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 (i.e., 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. Unfortunately, recent data suggests that pet scanning may not be as useful as once thought as a routine screening tool. These studies have a significant false positive rate (the test indicates a potential malignancy, although none is present ) which can lead to unnecessary and potentially harmful biopsy..
- PET scan is a 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.
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