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Archived Issues of Radiology Rounds
MGH Department of Radiology Website
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Evaluating Pulmonary Nodules
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| Note: Updated issue available (August 2006) |
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- Pulmonary nodules smaller than 4 mm have a very low risk (<1%) of being cancerous;
follow up CT scans are recommended per algorithm below
- Pulmonary nodules between 4-8 mm have intermediate risk (about 6%); follow up CT scans
recommended unless patient is high risk then consider PET or diagnostic intervention
- Pulmonary nodules greater than 8 mm are suspicious for cancer and fine needle aspiration (FNA)
biopsy is recommended or, in some cases a PET scan or VATS may be considered
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Solitary
pulmonary nodules are common incidental findings in chest x-ray or CT
images, with around 150,000 new nodules found each year in the United
States. They are defined as approximately round lesions less than 3 cm
in diameter, surrounded by normal lung parenchyma. Anything larger than
that is defined as a mass and is likely to be cancerous.
Once a nodule is found, the first step in the evaluation is to compare
it to previous images to establish if it is a new finding or, if it is
not, whether it is stable or increasing in size. The vast majority of
nodules that have been shown to be stable for greater than two years
are benign. If there are no previous studies and the nodule was
detected on a chest radiograph, the next step is to evaluate it with
CT. In some cases, CT can definitively show that the nodule is benign
from the pattern of calcification that may be found in granulomas and
hamartomas or from the presence of fat that may be present in
hamartomas. If the diagnosis is not definitively benign, follow up is
dependent on the size of the nodule and risk factors, such as an
underlying history of malignancy or heavy smoking.
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A & B Sequential images of the same patient showing pulmonary nodule changes that are suspicious for malignancy.
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If the nodule is smaller than 4 mm, it is too small to biopsy
percutaneously or to evaluate with a PET scan. As more than 99% of
incidentally detected, non-calcified nodules <4mm are benign, the
best option is to watch and wait, with follow up CT scans 12 and 24
months after the initial scan. If no growth has been detected after two
years, the nodule can be assumed to be benign. If the patient has a
history of malignancy, follow-up CT scans are recommended at 3, 6, 12,
and 24 months after the scan, unless there is growth. If there is no
growth, CT follow-up will continue as per clinical protocol.
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A
12 mm pulmonary nodule in right upper lung with a calcification pattern
indicating that this is a benign hamartoma or granuloma.
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Incidentally
detected non-calcified nodules between 4 and 8 mm are in the
intermediate risk category for malignancy. In patients without any
history of cancer, approximately 94% of nodules of this size are
benign. Risk factors, such as age, history of cigarette smoking or
significant second hand smoke exposure, and the clinical situation play
a role in deciding the next steps for these patients. In most cases, it
is best to watch and wait, with follow-up CT scans obtained at 3, 6,
12, and 24 months. In selected cases in which clinical risk factors of
cancer are high or in which nodule characteristics such as spiculation
suggest a much higher likelihood of malignancy, FNA biopsy or a PET
scan should be considered.
Nodules
larger than 8 mm are regarded as suspicious for malignancy, because
approximately 50% of incidentally detected nodules of this size are
malignant. Unless biopsy is contraindicated, it is recommended that
percutaneous CT guided FNA biopsy be performed, which will provide a
definitive diagnosis with an accuracy of about 90% for malignant
lesions and 60-80% for specific benign lesions. In some cases, where
the lesion is close to a central bronchus, bronchoscopy with
transbronchial biopsy can be considered. Relative contraindications for
FNA biopsy include patients who are ventilated, have severe emphysema,
have had a pneumonectomy, are on anti-coagulant therapy, or have
pulmonary arterial hypertension. If it is not possible to perform FNA
biopsy, the choices are to perform a PET scan or surgically remove the
nodule, using video assisted thoracoscopic surgery (VATS).
In
any case in which a nodule is increasing in size, no matter what the
initial size, it should be considered suspicious for malignancy and
intervention considered. In cases in which characteristics of any size
nodule suggest an inflammatory process, a short-term follow-up CT is
recommended after 4-6 weeks to assess for resolution or progression.
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Advantages and Disadvantages of Biopsy and PET
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Both
PET and FNA biopsy are not as reliable for diagnosis of lesions smaller
than 8 mm as they are for larger nodules. Tumors smaller than 8 mm and
those with a low metabolic rate may not be detected by PET. In
addition, inflammatory lesions, such as granulomatous lesions can also
appear in PET scans, resulting in false positive findings for cancer.
Histological examination of the cells withdrawn by FNA biopsy can
differentiate between malignant and infectious lesions, such as TB and
fungal infections, which may need medical treatment. In addition, the
type of malignancy can be identified, which can help in determining
which patients are candidates for surgery or chemotherapy.
FNA biopsy is associated with a significant number of minor
complications. As many as 20% will have a small pneumothorax and 1-2%
will have a pneumothorax large enough to require a chest tube. In
addition, some patients will experience minor hemoptysis.
Although PET is more expensive that FNA, it does have the advantage of
acquiring whole body images in cases of suspected lung cancer, which
makes it possible to discover distant metastases outside of the lung.
It is, therefore, a valuable tool for staging cancer.
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Fine needle aspiration (FNA) biopsy of a suspicious pulmonary nodule.
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Advantages |
Disadvantages |
| Fine Needle Biopsy |
Histological diagnosis |
Cannot be performed on lesions < 8 mm
Minor pneumothorax, 20%
Significant pneumothorax, requiring chest tube, 1-2%
Minor hemoptysis, 2-5%
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| PET |
Whole body image detects extra-pulmonary tumors
Can stage known lung cancer
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Cannot detect lesions < 8 mm
False positives from inflammation
False negatives from tumors with low metabolic rate
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| VATS |
Definitive histological diagnosis |
General anesthesia
Hospitalization, 1-3 days (longer in cased of prolonged air leak in 35%)
Arrhythmia, 3-4%
Bleeding, 4%
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Patient Preparation and Procedures
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No specific patient preparation is necessary for CT. For details about preparation for PET, see
May 2004 newsletter.
Patients
should not eat any solid food for 6 hours prior to FNA biopsy. They may
drink clear liquids up to 3 hours before the procedure. Diabetics
taking insulin should take half their normal 24 hour dose in the
morning and those on oral diabetic medication should not take it the
night before or the morning of the procedure. Patients must have
normal coagulation. Anticoagulant medication, including aspirin, should
be discontinued for 7 days prior to a FNA.
Patients
will receive light conscious sedation during the FNA biopsy. After the
procedure, patients will need to lie quietly for 3-4 hours in the
radiology recovery area. Prior to discharge, chest x-rays will be
performed to check for complications such as pneumothorax and bleeding.
Biopsy results will usually be ready within 3-4 days.
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PET/CT scan showing high metabolic activity in pulmonary nodule, indicative of cancer or inflammation.
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Scheduling
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Further Information
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PET and CT examinations may be scheduled online through Radiology Order
Entry (ROE) or by calling 617-724-XRAY (617-724-9729). A consultation
for FNA biopsy of the lung can be requested by calling 617-724-4254 or
by faxing a Thoracic Biopsy Approval form (Download pdf) available on the MGH Radiology Department website. |
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For further questions on pulmonary nodules, please contact Dr. Jo-Anne Shepard, jshepard@partners.org Director of Thoracic Radiology (617-726-4256) or Dr. Michael Lanuti, mlanuti@partners.org, Assistant in Thoracic Surgery (617-726-6751).
This article provided useful information about the appropriate use of imaging studies:
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References
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Gould, MK, Sanders, GD, Barnett, PG, Rydzak, CE, et al. (2003) Cost-effectiveness of alternative management strategies for patients with solitary pulmonary nodules. Ann Intern Med 138: 724-35
Henschke, CI, Yankelevitz, DF, Naidich, DP, McCauley, DI, et al. (2004) CT screening for lung cancer: suspiciousness of nodules according to size on baseline scans. Radiology 231: 164-8.
Libby, DM, Smith, JP, Altorki, NK, Pasmantier, MW, et al. (2004) Managing the small pulmonary nodule discovered by CT. Chest 125: 1522-9
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Ost, D, Fein, AM and Feinsilver, SH. (2003) Clinical practice. The solitary pulmonary nodule. N Engl J Med 348: 2535-42
Yankelevitz, D, Henschke, C, Westcott, J et al. (2000). Work up of the solitary pulmonary nodule.
(Download pdf) |
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