Diagnosis of SPN
SPNs (solitary pulmonary nodules) are usually asymptomatic and discovered by chance on a chest x-ray performed for another reason.
After the nodule is discovered and the patient's medical history is reviewed, the cause of the SPN may still be unknown.
Diagnosing the underlying disorder and determining an appropriate course of treatment depend in large part on the patient's risk for lung cancer. A biopsy (i.e., removing a sample of the abnormal tissue and analyzing the cells under a microscope) is necessary to confirm or rule out cancer. Certain features of the nodule that can be seen on a CT scan help determine the likelihood of a malignancy and the necessity for biopsy. If the nodule appears benign on the CT scan and the patient is at low risk for lung cancer, it is less likely that a biopsy is immediately necessary. Not all patients require a biopsy; however, all pulmonary nodules require close monitoring.
Medical History & SPN Diagnosis
It is important that patients communicate openly and honestly with their physicians about symptoms and risk factors. In patients with a history of neoplasm (benign or malignant) or a tumor elsewhere in the body, there is at least a 50 percent chance that the nodule is malignant.
Even a minor skin tumor may be significant and may influence the diagnosis and the choice of diagnostic tests. If there is no evidence of tumor elsewhere in the body and no history of benign or malignant tumors, there is a 60 to 95 percent chance that the nodule is benign.
Other illnesses that may have relevance include rheumatoid arthritis and any of the granulomatous diseases.
Factors to consider when making the diagnosis include the following:
- the patient's smoking history (Smoking is a risk factor for bronchogenic carcinoma.)
- where the patient lives or has lived in the past (Certain infections that can lead to SPN are endemic to certain geographic areas)
- exposure to mycobacterial disease (e.g., tuberculosis), which may cause SPN
- past chest x-rays that can help determine if and how quickly the SPN is growing and whether it is cancerous
Past chest x-rays may be the most useful in making the diagnosis. By examining changes in the nodule over time, the physician or radiologist can determine how fast it is growing and whether its growth is typical of a benign or malignant SPN.
Specific diagnostic tests depend on the risk for cancer and the likelihood that the SPN is malignant. Even though solitary pulmonary nodules are easy to see on an x-ray, they are difficult to biopsy or remove without invasive surgery.
One of the goals of diagnosing SPNs is to avoid unnecessary invasive procedures, such as surgically removing a noncancerous lesion. Clinical tests include evaluating growth in the size of the nodule by examining past chest x-rays, CT scan(s), and laboratory tests.
Based on the medical history and clinical diagnosis, the following factors indicate that the nodule is likely benign:
- volume doubling time less than 30 days or greater than 500 days
- lesion that is calcified (i.e., has an abnormal deposition of calcium salts) and the pattern of calcification is typical of a benign nodule (usually a central, clustered, or layered pattern)
- patient is younger than 30–35 years old
- absence of symptoms
- lesion is less than 2 cm in diameter
- margins of the lesion are smooth (evident on a CT)
- patient has never smoked
- patient lives in an area with a high incidence of histoplasmosis or coccidioidomycosis
If there are no risk factors for cancer, a PPD skin test should be done to determine the likelihood of tuberculosis, and a chest x-ray should be performed in 1–2 months. If the SPN remains the same size, a chest x-ray should be repeated in 2-4 months for two visits.
Based on the patient's medical history and clinical diagnosis, factors that increase the chance that a nodule is malignant include:
- nodule doubling time is between 1 and 6 months
- patient has a history of smoking
- patient is occasionally symptomatic
- patient is more than 45 years old
- lesion is greater than 2 cm in diameter
- lesion has indistinct margins
- there is no calcification
If there is any question concerning possible malignancy, the tissue should be biopsied. There are two types of biopsies commonly performed in patients with SPN: fiberoptic bronchoscopy and percutaneous, or transthoracic, needle biopsy. There are risks and benefits in both procedures, and the patient should gather as much information as possible from the physician before making a decision.
Many physicians evaluate whether the patient is a candidate for surgery by conducting pulmonary function tests. If the patient performs well on the tests and the nodule is going to be surgically removed, a separate biopsy may not be necessary. This is especially true of the percutaneous needle aspiration because it yields too many false positives to be reliable and often produces indeterminate results. Pulmonary function tests are used to evaluate a patient's risk for surgery.
SPN & Ruling Out Infectious Disease
Besides determining whether the nodule is benign or malignant, another important step in diagnosing SPNs is ruling out infections, such as a fungal infection or pneumonia. This is especially important if a patient shows symptoms suggestive of an infectious disease (e.g., fever, malaise, cough). If the lesions may be symptomatic of a bacterial infection, such as pneumonia, the physician may prescribe antibiotics and follow up with repeat chest x-rays to see if the lesions disappear.