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Updated 2017 Fleischner Society guidelines advise a less intensive approach to the management of most small pulmonary nodules incidentally discovered on CT scans. The Fleischner Society now recommends that solid nodules 6 mm or less in diameter in low-risk adults >35 years old generally need no further follow-up. In higher-risk patients, a follow-up CT scan should be considered optional. The recommendations apply even if multiple solid pulmonary nodules ≤6 mm are present.
Previous Fleischner Society guidelines had advised no follow-up in solid nodules ≤4 mm in low-risk patients, and a single follow-up CT scan in 12 months in high-risk patients with solid nodule(s) ≤4 mm.
The change may not seem like much. But the new guidelines should eliminate thousands of unnecessary follow-up CT scans performed each year in the approximately 1.5 million people in the U.S. with pulmonary nodules, the vast majority of which are harmless. Since CT scanning can rarely cause cancer, the updated guidelines might prevent a few cancer cases that would be caused by CT scanning. (For reference, the cumulative risk of cancer caused by lung cancer screening over 10 years with low-dose CT has been estimated at 1 in 2,000.)
The Fleischner Society considers patients high-risk if they have a significant past smoking history or other known risk factors (see below), and low-risk if they lack these factors. Importantly, characteristics of both the nodule and the patient contribute to the risk assessment.
For 6-8 mm Nodules, Third CT Optional in Low-Risk Patients
For solid nodules 6-8 mm in diameter, only a single follow-up chest CT at 6-12 months is advised, with a third CT scan at 18-24 months to be "considered". Previous editions of the guidelines advised the third CT scan as standard. High-risk patients are still advised to undergo a CT scan at 18-24 months if the nodules are unchanged at 6-12 months.
What Does "Optional CT" or "Consider CT" Mean?
The revised guidelines warn that
although the risk of cancer in nodules smaller than 6 mm is considerably less than 1%, even in patients at high risk ... suspicious morphology, upper lobe location, or both can increase cancer risk into the 1%–5% range; therefore, follow-up at 12 months may be considered, depending on comorbidity and patient preferences.
Scanning earlier than 12 months is not advised, because
such small nodules, if malignant, rarely advance in stage over 12 months, whereas a short-term follow-up examination showing no apparent change may provide false reassurance."
Longer Interval Advised Between Scans for High-Risk Patients
For high-risk patients with solid nodules 6-8 mm, prior guidelines advised a follow-up CT scan at 3-6 months; a 6-12 month interval is now advised. The reasoning is similar to the previous section (smaller nodules tend to be slower growing); scanning too early may provide false reassurance in the interval before the next scan.
What About Subsolid Nodules?
Subsolid nodules and part-solid nodules can be slow-growing and require extra vigilance by physicians. The management of subsolid and ground glass pulmonary nodules is reviewed here.
What to Do About Multiple Solid Nodules
The advised follow-up for multiple solid pulmonary nodules <6 mm in diameter is the same as for single nodules <6 mm: no follow-up advised for low-risk patients; optional chest CT in 12 months for higher-risk patients.
For multiple nodules 6-8 mm, all patients (low- or high-risk) are advised to get a follow-up chest CT in 3-6 months. High-risk patients are advised to undergo another chest CT at 18-24 months, while one should be "considered" at 18-24 months for low-risk patients. The most suspicious-looking nodule should guide management and risk stratification.
Pulmonary Nodules: Who's Low Risk, Who's High Risk?
The Fleischner Society advises that physicians assign risk according to the categories proposed by the American College of Chest Physicians (ACCP):
Low risk, which corresponds to an estimated risk of cancer of less than 5%, is associated with young age, less smoking, smaller nodule size, regular margins, and location in an area other than the upper lobe.
To estimate high risk, we recommend combining the ACCP intermediate-risk (5%–65% risk) and high-risk (>65% risk) categories. High-risk factors include older age, heavy smoking, larger nodule size, irregular or spiculated margins, and upper lobe location. Subjects with intermediate risk share both high- and low-risk characteristics.
It's unclear why "low risk" is described as less than 5% cancer risk in this section, while the Fleischner Society seems to consider low risk to be <1% elsewhere in its guidelines. Many patients would probably view a 1 in 20 chance of having cancer (=5%) as being uncomfortably high.
Fleischner Society Pulmonary Nodule Guidelines: Limitations
The Fleischner Society is an international, multidisciplinary collaboration primarily dedicated to the radiographic diagnosis of diseases of the chest. Their guidelines on the radiographic management of incidentally discovered pulmonary nodules have defined the standard of care.
As with any approach to medicine (algorithmic or individualized), the Fleischner Society guidelines contain embedded value judgments. Chief among these is that when risk of cancer is estimated at less than 1%, it is ethical not to offer additional testing. Applied to populations, this accepts a small number of missed cancers, in favor of sparing of thousands of people from useless or (rarely) harmful scanning.
The Fleischner Society Guidelines have never been prospectively validated. Their authority derives from expert consensus on the existing research on the natural progression of small pulmonary nodules, as well as the imprimatur of both the Radiological Society of North America and the American College of Chest Physicians. The guidelines' actual performance characteristics in large real world populations -- sensitivity, specificity, the rate of false negatives (missed cancer diagnoses), or complications resulting from false positive scans -- are unknown.