Tuesday, February 16, 2010

Question: "They found a pulmonary nodule on a CT scan, what does this mean?"

Answer: This is a very common question/issue. What a pulmonary nodule means to you depends on a lot of factors.
What does a pulmonary nodule look like?
  • A pulmonary nodule is basically a small focus of tissue in the lung. It is usually round but can often be oval, irregular, or speculated. Sometimes is can be calcified or have fat density.
  • By definition a nodule is less than 3cm in size. If the lesion is greater than 3cm, it may be the exact same tissue etiology, but it is now called a mass.

What could it mean?
  • Fat density in a nodule is considered benign.
  • If calcifications are seen within a pulmonary nodule it is almost always benign as well.
  • Calcifications are associated with prior or chronic inflammation/infection. In this scenario, the nodule is the tissue that is left over after your immune system has taken care of the problem. It is kind of like a scar.
  • These “scars” do not always calcify and a non-calcified nodule can be more difficult to evaluate. None the less, a noncalcified-nodule can still represent the benign residue of a prior infection, but it is hard to tell for sure. So that is usually the major question; is the nodule cancer or not?
So how can you tell if it is cancer?
  • The good news is that the vast majority of lung nodules are benign.
  • The bad news is, if the nodule is not calcified or does not have fat, it can be difficult to impossible to tell on one CT scan if a nodule is cancer or not.
  • Because cancers grow and scars generally do not, a follow-up scan can help. Scans at different times provide a reference point to evaluate if it increases in size over time. Some types of cancers grow very slow and therefore a long follow-up may be necessary to feel comfortable that the nodule is benign.
  • Other factors play a role in the likelihood that a nodule is a cancer or not. The chances that a nodule is malignant increases with nodule size. Some other common factors that increase the likelihood that a nodule could be cancer is; patient age, history of other cancers, smoking history and history of other carcinogen exposure.
How often do you re-scan with CT and for how long?
  • This is a major issue that is debated by many.
  • In the last decade several articles have been published in major peer reviewed medical journals to try to establish a safe and rational approach to the management of this common issue. Most recently, in 2005 a consensus guideline was created and adopted by the major medical society on chest imaging (the Fleischner Society). Their follow-up algorithm is very helpful but remains general and many other individual factors will dictate management. The article is online:
  • http://radiology.rsna.org/content/237/2/395.full
  • As you can see from this guideline, nodules less than 4mm are considered benign in low risk patients.
  • I believe this is the size of the nodule you have on the CT scan (reference to the person asking the question).  However, a 4 mm nodule is not considered benign in high risk patients.
  • The type of cancer you are dealing with (desmoid fibroma) is not known to metastasize to the lungs and therefore it is questionable if you should even be in the high risk patient category.
  • These guidelines have been used by many, but not by all. For example, at MGH, they have a slight modification to the Fleischner Society recommendations based on their own experience.


This algorithm was used when I was at MGH. However, things in medicine often change with medical advances and it is possible that it has been updated since.

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