Tests Used to Diagnose SPN
Chest X-ray and SPN Diagnosis
One of the first things done to clinically evaluate an SPN is to compare the most recent chest x-ray with older x-rays, if any are available. This is extremely important because the growth rate of a nodule is a more reliable indicator of malignancy than a one-time x-ray or CT scan. The doubling time of most malignant SPNs is 1 to 6 months, and any nodule that grows more slowly or more quickly is likely benign.
CT (computed tomography) Scan and SPN Diagnosis
Nearly all SPNs discovered on chest x-rays are followed up by a CT scan. A CT scan, especially a thin-section CT, can provide 10 to 20 times more detail than a conventional chest x-ray and is an invaluable aid in identifying features of the nodule and determining the likelihood of cancer.
CTs localize SPNs more accurately, provide more detail of the internal structures, and show calcifications more readily.
Because of the high cost and increased radiation exposure, a chest x-ray should always precede a CT scan. In the case of SPNs, however, a CT scan is usually considered an essential follow up to the chest x-ray.
Based on the morphology of the nodule (i.e., what it looks like), the physician and/or radiologist determines what to do next. Sometimes more invasive diagnostic procedures are necessary and sometimes they are not.
The CT scan also provides information about which biopsy approach is best. It can show the presence or absence of airways leading to the nodule. If the nodule is located in or near an airway, a bronchoscopy (which involves inserting a tube through the airway) is an appropriate next diagnostic step. A CT scan can also reveal additional nodules that are usually an indication of granulomatous disease or metastatic cancer from other parts of the body.
How a nodule looks (i.e., its size, shape, pattern of calcification, and whether there are any surrounding, or "satellite" lesions) provides important clues about whether or not it is cancerous.
Usually, benign nodules are small (less than 2 cm in diameter), have smooth, well defined margins, and tend to be symmetrical and spherical. Benign nodules are often calcified, a property that can be seen on chest x-ray or CT. The calcification is usually diffuse or lamellated (composed of thin, flat layers).
Dense calcification in the center of the nodule and diffuse calcification indicate granulomatous disease. The presence of fat is an indicator of a hamartoma (a benign abnormality). About 50 percent of hamartomas are partially comprised of fat tissue.
Malignant SPNs tend to have lobulated or shaggy borders, and there is usually some distortion of the adjacent blood vessels. A calcification pattern that appears irregular or spotty is a good indication of malignancy. Other characteristic features that may appear on the x-ray include a tail on the lesion and a corona radiata (a soft halo around the lesion).
Importantly, as essential as a CT scan is, there is no reliable morphological indicator of whether a nodule is benign or malignant. Generalizations can be made. Yes, benign SPNs tend to be smooth, but this does not mean that all smooth SPNs are benign. Each individual case must be evaluated. One possible exception is the presence of heavy calcification in the center of the lesion, this is a fairly certain characteristic of an old granuloma.
Laboratory Studies and SPN Diagnosis
Standard laboratory studies are usually performed, including a complete blood count (CBC), urinalysis, and a stool sample (to look for signs of blood). These tests are often invaluable in diagnosing systemic diseases or cancers that have originated elsewhere and metastasized in the lungs.
Cytological studies of sputum are helpful to identify large, centrally located nodules that have airway involvement (a positive result could preclude the need for more invasive tests, such as bronchoscopy or needle biopsy). However, examining the cells of the sputum rarely helps in diagnosing small or peripheral nodules. The false negative rate (producing negative results when there is a malignancy) can be as high as 80% or more.
If it is likely that the nodule is benign, a PPD skin test may be done to determine whether the patient has been exposed to the bacteria that causes tuberculosis. The test involves injecting the tuberculin antigen into the skin and observing the body's response. If the patient has been exposed to TB, the body will react and there will be swelling or redness at the injection site.
Positron Emission Tomography (PET) and SPN Diagnosis
PET has recently been used to diagnose SPNs. The procedure involves using a radiolabeled substance to measure the metabolic activity of the lesion. Malignant nodules absorb more of the substance than benign nodules and normal tissue and can be readily identified on the three-dimensional, colored image. The PET scan may be the most accurate, noninvasive diagnostic aid to date, but the procedure is expensive and its effectiveness is still being evaluated.
Pulmonary Function Tests and SPN Diagnosis
Pulmonary function tests evaluate how well the lung is functioning (i.e., how well the lungs are expanding and how much oxygen they are capable of handling). Pulmonary function tests are an essential part of determining whether a patient is a candidate for surgery or not.
A quantity called the "FEV1" is especially helpful (it measures the amount of air exhaled after full inspiration) and is an excellent indication of pulmonary function. If it is too low, it is more likely that the patient will suffer complications, as a result of the surgery.
Fiberoptic Bronchoscopy Biopsy and SPN Diagnosis
Fiberoptic bronchoscopy is an essential diagnostic tool for many respiratory disorders, including SPNs. More than 70 percent of all lung cancers can be biopsied using this technique.
The procedure involves inserting a flexible tube through the mouth or nose, into the airway, and to the lungs. This enables the doctor to view the tissue inside the lungs (either directly or on a TV monitor) and biopsy (collect a small sample of) abnormal-looking tissue for microscopic examination. The tissue is examined under the microscope to confirm the diagnosis. The procedure is painless (patients are given relaxation medication and a local anesthetic) and normally takes from 15 minutes to an hour.
There are several different ways to biopsy the airway or lung tissue where the SPN is located. If the lesion is on the wall of an airway, the tissue can be washed with a saline solution and suctioned or brushed with a soft brush.
If the lesion is not easily accessible on the airway wall, a needle biopsy or a forceps biopsy may be done. A needle biopsy involves using a small needle tool to collect cells on the other side of the airway wall. A forceps biopsy involves using forceps to sample an area of tissue.
If the SPN is deep within the lung, a technique called fluoroscopy may be used during the bronchoscopy. Fluoroscopy involves using x-rays to examine tissues and guide the biopsy.
Studies have shown that the most sensitive bronchoscopy biopsy involves a brush biopsy, followed by a tissue biopsy (either needle or forceps) and wash. This combination of techniques provides the best sample of cells.
As in any medical procedure, there are potential complications. The complications of this particular procedure are rare and usually minor. They include hemoptysis (coughing up blood), which is usually minor and disappears on its own, and pneumothorax (the presence of air or gas in the pleural cavity, the area of the chest outside of the lungs). Pneumothorax occurs in about 5 percent of bronchoscopy patients and may require that a tube be inserted through the chest wall to drain the excess air. In a study conducted in the United Kingdom, fiberoptic bronchoscopy biopsies of SPNs had a complication rate of 0.12 percent and a mortality rate of 0.04 percent. The deaths were reportedly due to inappropriate sedation. About 70 percent of all malignant SPNs can be biopsied using this technique.
A bronchoscopy is usually performed when:
- the lesion is located in the hilum (the part of the lung where the bronchi and blood vessels enter and leave) or midlung;
- there is evidence of airway involvement, and/or
- CT scan shows an airway leading to the nodule.
Transthoracic, or Percutaneous, Needle Biopsy (TNB or TTNB) and SPN Diagnosis
Transthoracic needle biopsy is a technique to diagnose lung cancer that has been used for over 100 years. It involves inserting a needle into the chest wall as close to the SPN as possible and guiding the position of the needle using either fluoroscopy or CT.
When the tip of the needle is inside of the lesion, a syringe is used to aspirate (suck out) cells for microscopic analysis. Because the tissue sampling involves aspiration, the procedure is sometimes known as transthoracic needle aspiration biopsy. Needle biopsies provide an accurate diagnosis of malignant nodules 75 to 95 percent of the time and 5 to 25 percent of malignant nodules are not identified properly.
A transbronchial biopsy yields a very small amount of tissue and the pathologist may not be able to provide a definitive diagnosis. Preliminary studies have shown that if the tissue is examined by the pathologist immediately, rather than after a period of time has passed, the accuracy of the diagnosis improves greatly.
Potential complications of TNB include pneumothorax (in about 20 percent of all cases) and hemoptysis.
The procedure should be done to provide helpful information about how to treat the nodule, because it produces too many false reports. It should be done only when cells cannot be sampled using the bronchoscope and should not be done if the patient may not be able to withstand pneumothorax that could result.
When it is not clear whether the biopsied tissue is malignant or benign there are several options, depending on the patient's risk for cancer.
If it is likely that the nodule is benign, another biopsy could be done; or the patient may adopt a wait-and-see attitude.
The doubling-time of the nodule could be measured by a series of repeat chest x-rays to determine its malignancy status. Small lesions generally do not grow quickly and could be monitored closely. The nodule should be watched for changes for a total of 2 years.
If it is likely that the nodule is malignant, the biopsy could be repeated, the patient could adopt a wait-and-see attitude and undergo regular observation, or the patient might opt for immediate surgical removal and biopsy of the nodule. Factors to consider when deciding if surgery is the right choice, include the patient's willingness to undergo surgery and the risk for complications during and after surgery. Many physicians question the usefulness of a biopsy if the patient is a candidate for surgery and is going to need surgical removal (i.e., if the nodule is malignant).