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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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- Pulmonary nodules ≤4 mm have a low risk of being cancerous; nodules between 4-8 mm are of
intermediate risk for cancer; follow up CT scans for both categories are recommended on different schedules
- Pulmonary nodules >8 mm and mixed solid/ground glass nodules are suspicious for cancer;
percutaneous needle aspiration biopsy (PNAB), positron emission tomography (PET), or video
assisted thoracic surgery (VATS) should be considered
- A detailed guideline algorithm for the management of pulmonary nodules found on chest x-ray
or CT is presented
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Increased
utilization of chest CT examination has resulted in a dramatic
escalation in the number of newly detected solitary pulmonary nodules,
defined as round lesions <3 cm in diameter surrounded by lung
parenchyma. Although the risk of finding cancer is 30-40% in
radiographically discovered pulmonary nodules, thin section CT is 10-20
times as sensitive and can detect much smaller nodules. Size is
an important predictor of the likelihood of malignancy and recent
evidence indicates that pulmonary nodules ≤4 mm have an extremely small
risk of cancer, especially in those with no history of cancer. In light
of this new evidence, fewer short-term follow-up CT scans are necessary
for most patients with small pulmonary nodules. Therefore, new
recommendations have been developed for patient follow-up that varies
according to the risk of cancer.
In some cases, benign
nodules (granulomas, hamartomas) can be definitively diagnosed by CT
examination because they have distinctive patterns of calcification and
fat (which are not found in malignancies) (Figure 1). If the diagnosis
is not definitively benign, follow up is dependent on the patient’s
risk factors for cancer and the size and imaging characteristics of the
nodule.
The first step is to establish if the nodule is a new finding or, if
not, whether it is stable or increasing in size. This requires
comparing it to any available previous images (Figure 2). If there are
no previous images and the nodule was detected on a chest radiograph,
the next step is to evaluate it with CT.
Nodules with Low to Intermediate Risk for Cancer
The
likelihood of malignancy is <1% for nodules ≤4 mm and 6% for those
between 4-8 mm. Nodules <8 mm are too small to biopsy percutaneously
or to evaluate with a PET scan. Therefore, the best option is to watch
and wait, with follow up CT scans at intervals that depend on nodule
size, patient age, history of malignancy, and likelihood of infection
(Figure 2). Patients aged 18-35 yrs have a much smaller
likelihood of malignancy than older adults (<1% of all lung
cancers). Therefore, unless there is a history of malignancy, less
rigorous follow-up CT is recommended than for older patients with
nodules ≤8 mm.
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Figure 1.
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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Nodules Suspicious for Malignancy
Approximately 50% of incidentally detected nodules >8 mm are
malignant. Malignancy should be suspected in a patient with a prior
history of cancer or in any case in which a nodule is increasing in
size, has spiculated margins or mixed solid/ground glass attenuation.
Patients of any age with a history of cancer should have close follow
up intervals because metastases demonstrate more rapid growth (Figure
2). Diagnostic intervention should be considered for nodules >8
mm. Percutaneous needle aspiration biopsy (PNAB) will provide a
definitive diagnosis with an accuracy of about 90% for malignant
lesions and 60-80% for specific benign lesions. In cases in which the
lesion is close to a central bronchus, bronchoscopy with transbronchial
biopsy can be considered.
FDG-PET scans are useful in identifying metabolically active nodules
that may require diagnostic biopsy, information that is particularly
helpful in patients with significant co-morbidities.
Relative contraindications for biopsy include mechanical ventilation,
severe emphysema, prior pneumonectomy, anti-coagulant therapy, or
pulmonary arterial hypertension. In addition, it is technically
difficult to obtain definitive results with PNAB on pulmonary lesions
close to the diaphragm. If it is not possible to perform PNAB, the
choices are to surgically remove the nodule using video assisted
thoracoscopic surgery (VATS), or perform follow-up CT scan (Figure 2).
Follow up is not necessary once a nodule has been demonstrated to be
stable for 24 months, with the exception of nodules that have ground
glass features on CT (Figure 3). Longer follow up is warranted
because these features can be indicative of indolent cancers that can
be stable or very slowly growing over several years.
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| Figure 2. MGH Guideline Algorithm for Evaluating Pulmonary Nodules. |
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Figure 3. (A) CT image showing ground-glass nodule in right upper lobe of the lung. (B)
Follow-up scan of the same patient 20 months later reveals progression
to a mixed ground-glass/solid tumor. VATS confirmed that the lesion was
malignant (adenocarcinoma).
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Nodules Suspicious for Inflammatory Processes
In patients who are immunocompromised or febrile, the possibility of an
infection should be considered. For these patients, short-term
follow-up CT is recommended in ≤4-6 weeks and then to resolution.
Alternatively, diagnostic intervention with PNAB, bronchoscopy, or VATS
can be considered as clinically indicated (Figure 2).
Modalities for Evaluation of Nodules
Once a nodule has been classified as suspicious by CT evaluation, it
can be further evaluated with PNAB, FDG-PET, or VATS. Table 1
compares the advantages and disadvantages of these modalities.
Histological examination of the cells obtained by PNAB (Figure 4) can
frequently differentiate between malignant and infectious lesions, such
as TB and fungal infections. In addition, the type of malignancy can be
identified, which can help in determining which patients are candidates
for surgery or chemotherapy. PNAB is associated with some 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.
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Figure 4. Percutaneous needle aspiration biopsy (PNAB) of suspicious pulmonary nodule.
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FDG-PET shows excellent sensitivity and specificity in detecting
malignant nodules > 8 mm (Figure 5). In addition, PET is more
accurate in detecting lymph node metastases in the thorax and provides
the added advantage of whole-body staging for lung cancer. Up to 11% of
patients with lung cancer have occult extrathoracic metastases detected
on PET that conventional staging missed. However, limitations in
resolution preclude effective characterization of nodules <8 mm. In
addition, certain tumors i.e. carcinoid, bronchioloalveolar cell
carcinoma, and well differentiated adenocarcinoma demonstrate
relatively low metabolic activity and are, therefore, not consistently
detected with FDG-PET. (However, most of these tumors have features on
CT that are suspicious for malignancy that would warrant further
diagnostic evaluation.) Inflammatory diseases may also appear positive
on FDG-PET scans, resulting in false positive findings for cancer. On
occasion a nodule due to mycobacterial or fungal disease, sarcoidosis
or organizing pneumonia will mimic a neoplastic pulmonary nodule. |
| Table 1. Comparison of modalities for evaluating pulmonary nodules |
Modality*
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Advantages |
Disadvantages |
| PNAB |
Histological diagnosis |
Low diagnostic yield for nodules < 8 mm
Minor pneumothorax, 20%
Significant pneumothorax, requiring chest tube, 1-2%
Minor hemoptysis, 2-5%
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| FDG-PET |
Whole body image detects extra-pulmonary tumors
Can stage known lung cancer
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Lower sensitivity for 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 2-15%)
Arrhythmia, 3-4%
Bleeding, 4%
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| *PNAB
= percutaneous needle aspiration biopsy, FEG-PET =
18-fluorodeoxyglucose positron emission tomography, VATS = video
assisted thorascopic surgery |
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Figure 5. PET/CT scan showing high metabolic activity in pulmonary nodule, indicative of cancer or inflammation.
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Patient Preparation and Procedures
For details about preparation for PET, see the Radiology Rounds article on PET/CT, May 2004. Pre-procedure preparation information for PNAB can be found on the Thoracic Radiology web site.
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Scheduling
Both
PET and CT examinations can be scheduled online through Radiology Order
Entry (http://mghroe
) or by calling 617-724-XRAY (617-724-9729). A
consultation for PNAB of the lung can be requested by calling
617-724-4254 or by faxing a Thoracic Biopsy Approval form
available on the MGH Radiology Department website. A consultation for
VATS may be obtained from the Multidisciplinary Thoracic Oncology
Clinic, 617-724-4000.
Further Information
For
further questions on pulmonary nodules, please contact
Jo-Anne Shepard, M.D.
, Director of Thoracic Radiology (617-626-4256) or
Michael Lanuti, M.D.
, Assistant in Thoracic Surgery (617-726-6751).
We would like to thank Jo-Anne Shepard, M.D., Michael Lanuti, M.D., and
Suzanne Aquino, M.D., for their advice and assistance in the
preparation of this article.
This article provided useful information about the appropriate use of imaging studies:
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References
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Pieterman RM, van Putten JWG, Meuzelaar JJ, et al. (2000) Preoperative staging of non-small-cell lung cancer with positron-emission tomography. N Engl J Med343:254-261
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
MacMahon, H, Austin, JH, Gamsu, G, Herold, CJ, Jett, JR, Naidich, DP, Patz, EF, Jr. and Swensen, SJ. (2005) Guidelines for management of small pulmonary nodules detected on CT scans: a statement from the Fleischner Society. Radiology 237: 395-400
Winer-Muram, HT. (2006) The solitary pulmonary nodule. Radiology 239: 34-49
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