Chapter Nine: The Solitary Pulmonary
The solitary pulmonary nodule, or SPN,
can pose a formidable diagnostic challenge. Also known as "coin
lesions", solitary pulmonary nodules are defined as single
nodules under 4 centimeters in diameter. (When the lesion is over
4 cm it is referred to as a "mass".) SPNs typically do
not contain a large amount of calcium, though CT scans often depict
density levels (Hounsfield units) which are consistent with calcification.
This feature will be discussed in more detail below.
The term "SPN" implies a lesion
that has indeterminate characteristics. In other words its origins
need to be investigated to exclude the possibility of a malignancy.
They are usually found by accident since their size causes few,
if any, symptoms.
Over half of all SPNs turn out to
be granulomas which are, of course, benign leftovers of an old
histoplasmosis, coccidioidomycosis or tuberculosis infection. Though
that statistic is comforting, keep in mind that 30% are primary
malignancies such as bronchial carcinoma or carcinoid tumors.
Metastatic lung disease, though extremely common, does not usually
manifest as an SPN. Patients usually present with multiple
pulmonary nodules instead.
There are important considerations after
an SPN is found.
The two most important
prognostic indicators are:
Less predictive prognostic indicators are:
- size of lesion
- age of patient
- smoking history
- location within the chest
Both malignant and benign nodules can grow. It is the rate of
growth which is most important. Malignancies are characterized
by uninhibited, exponential growth, and benign nodules should grow
more slowly. By comparing serial films, it is possible to calculate
the rate of growth. A lesion which takes 18 months to double in
volume, or one which takes less than 1 month to double, is generally
benign. (You might be wondering which benign process could demonstrate
such fast growth. The answer is that cysts and infections
can enlarge very quickly.)
The average time it takes for a malignant
nodule to double in volume is about 110 days. The "malignant
window" of the time in which malignancies typically double
is between 1 and 18 months (or 30 to 500 days).
How this works: take a measurement of
the diameter of the lesion on comparable chest x-rays from different
dates. A doubling time calculator is provided in a link below. It
is very important to remember that because of the spherical nature
of a nodule, a 9mm lesion that increases to 11mm in diameter
has doubled in volume. By the time a lesion of 5mm has increased
to 10mm it has more than quadrupled in size.
48 year-old woman with 30 pack-year history
of smoking. Note dense nodule in right lung base.
Same patient with an x-ray from 9 years
previous. Note there has been no change in size.
Calcification is a good thing. Less than 10% of all malignant SPNs
contain appreciable calcium. Most lesions which are calcified are
benign and they include granulomas, hamartomas and some rarer entities.
Calcification, however, is sometimes
hard to determine on a chest x-ray. A nodule may contain a good
amount of calcium and still not be discernible on the x-ray. When
in doubt a low kVp x-ray can help, however it is a CT scan
which is most important in making a determination of calcium content.
The unit of measurement
for density used in CT scanning is the Hounsfield Unit (HU),
after Sir Godfrey Hounsfield, the British Nobel laureate who developed
the CT scanner. The scanner is calibrated to reflect water as having
0 HU. Air measures at -1000 HU and bone at +1000
HU. Plain films are able to resolve only large differences in
tissue attenuation, e.g. air is more lucent than fat which is more
lucent than soft tissue, etc. CT computers can measure subtle differences
within soft tissue as the chart to the right depicts. Also, the
operator can manipulate an image to highlight certain tissues. These
variables are called "windows". A single study of the
chest may include "soft tissue windows" and "lung
A spiculated edge is ominous. It implies encroachment
into previously normal tissue. A well-defined border is a good thing
usually, but not always. Remember that cannon ball-type metastatic
nodules tend to have fairly well-defined edges.
Unknown Case 1
Unknown Case 2
Above are two cases of SPNs in different
patients, both adult women. (Apical lordotic projections are shown.)
Try to discern which has benign characteristics and which has malignant
Size of Lesion
The larger the nodule, the more likely it is to be malignant. Lesions
under 1cm are most likely to be benign and those over 3cm are likely
to be malignant. Those between 1cm and 3cm are a toss-up and, of
course, there can be very small malignancies and very large benign
Age of Patient
A person under the age of 30 is very unlikely
to have cancer. Of course there are exceptions. The incidence of
cancer increases with age so that someone over 70 with an SPN has
a great probability of cancer.
Click image to enlarge
Pack-year calculation: Average
number of cigarette packs smoked per day, multiplied by years of
smoking. The length of time spent smoking is important, too. The
longer a person smokes, the greater the risk. Example:
|Person "A" smoked
1 pack of cigarettes a day for 40 years. Person "B"
smoked 2 packs of cigarettes daily for 20 years. Both have smoked
for 40 pack-years. However, person "A" is 8 times
more likely to develop lung cancer.
CT scan showing SPN and a pack of cigarettes
in the upper right portion of the image.
Location within the Chest
A nodule within the upper lobe has a
greater probability of malignancy compared with nodules discovered
Summary of Features
Most valuable indicators
|Doubles in size between 1 and 18 months
||No growth; slow growth (over 18
months to double); or very fast growth (under 1 month
|No -- 90% have no calcification
Less valuable indicators
|Spiculated edge, or lobulated
||Well-defined, smooth edge
||Middle lobe and lower lobes
Differential Diagnosis of SPNs
Management of SPNs
As nearly everyone knows, an early diagnosis is associated with
better survival odds for most cancers. Prompt determination of the
cause of an SPN is essential and treatment options develop from
a knowledge of the origin of the lesion. A small well-defined, partially
calcified nodule in an otherwise healthy 24 year-old who has never
smoked can usually be safely watched at intervals of 3-6 months.
Conversely, a large, poorly defined, uncalcified nodule in a 40
pack-year smoker requires decisive action. Usually a work-up will
include noninvasive procedures like CT initially. If the index of
suspicion goes up with those results, a biopsy (often an excisional
biopsy) is undertaken. Cancer treatments depend of the stage at
which it is found, i.e. a cure is not realistic when cancer has
spread to distant parts of the body, so life extension with care
to consider quality of life issues is often the path taken.
If you find a solitary pulmonary nodule, the first thing to do
is to determine whether or not films of the same region are available
which will help you determine the rate of growth.
If, like the case above, serial films show no change over time,
it is safe to declare the nodule benign. There may be other compelling
clinical reasons to go forward with further tests, however. When
plain films leave important questions unanswered, a CT scan can
characterize the lesion in terms of Hounsfield Units.
Note small nodule seen with tomography
Same case with CT scan
Note cursors placed for accurate measurement
At this point it is a good idea to reflect on
whether the chiropractor can efficiently manage an
SPN with the current state of affairs in health care. As chiropractors,
we are not always well connected to the larger health care
community, and taking responsibility for collecting all the
data and assembling it to make critical treatment decisions
is probably not realistic for most of us.
Also, SPNs are very common litigation cases
in medicine for lesions missed, misinterpreted or mismanaged.
Nearly half of the cases are settled in favor of the litigant.