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I.
Imaging of the Solitary Pulmonary Nodule
II.
Authors
Anil K. Attili, AFRCS, FRCR
Lecturer in Thoracic Radiology
Department of Radiology
University of Michigan
Ann Arbor
Tel- 734-647-9780
e-mail- aattili@med.umich.edu
Ella A. Kazerooni, MD, MS
Professor and Director of Thoracic Radiology
Department of Radiology
University of Michigan
Ann Arbor
Tel- 734-936-4366
Fax-734-936-9723
e-mail- ellakaz@med.umich.edu
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III.
Issues:
1.
The solitary pulmonary nodule:
A. Who should undergo imaging?
Special case: Estimating the probability of malignancy in
a solitary pulmonary nodule
Special case: Solitary pulmonary nodule in a patient with a
known extrapulmonary malignancy
IV.
Key Points:
-
Further evaluation of a solitary pulmonary nodule incidentally detected on chest
radiography is not needed when either of the following two criteria (MODERATE
EVIDENCE) are met:
1) Nodule is stable in size for at least two years when compared to prior chest
radiographs.
2) There is a benign pattern of calcification demonstrated on chest radiography.
-
Further evaluation of a pulmonary nodule showing either a benign pattern of
calcification, fat and/or stability for 2 years or more on thin-section CT is not needed
(MODERATE EVIDENCE)
-
In the absence of benign calcification, fat or documented radiographic stability for at least
two years, the choice of subsequent imaging strategy to differentiate between benign and
malignant nodules is critically dependent on the pretest probability of malignancy.
2
a) CT should be the initial test for most patients with radiographically indeterminate
pulmonary nodules. (MODERATE EVIDENCE)
b)
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FDG -PET has a high sensitivity and specificity for malignancy. (STRONG
EVIDENCE), and is most cost-effective when used selectively in patients where the
CT findings and pretest probability of malignancy are discordant.
-
Multidetector CT scanners with improved spatial resolution, and the use of MDCT for
lung cancer screening, have led to the increased detection of small (< 1 cm) pulmonary
nodules. Nodules are categorized on CT as either i) solid ii) part-solid (mixed solid and
ground glass attenuation) or iii) non-solid (pure ground glass attenuation).
The imaging strategy for the further evaluation of small solid pulmonary nodules in the
absence of a known primary malignancy is based on nodule diameter (MODERATE
EVIDENCE)
1. For 4-10-mm in diameter solid nodules, a strategy of careful observation with serial
thin-section CT scanning is recommended at 6, 12 and 24 months. In patients with a
known primary neoplasm, initial re-evaluation at 3 months is recommended.
2. For solid nodules larger than 10-mm in diameter, further evaluation with either
18
FDG -PET, percutaneous needle biopsy or video assisted thoracoscopic surgery
(VATS) is recommended.
-
Part-solid nodules (solid and ground glass components) and non-solid nodules (pure
ground glass) detected at lung cancer screening have a higher likelihood of malignancy
than solid nodules; therefore, tissue sampling (percutaneous CT-guided biopsy or VATS)
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is recommended (MODERATE EVIDENCE). For nodules less than 1-cm where this may
not be possible, close serial CT evaluation at 3 month intervals in recommended.
4
Issue 1: Who should undergo imaging?
Summary: Pulmonary nodules are commonly discovered incidentally on chest radiographs or
computed tomographic (CT) examinations. There are four imaging findings that are highly
predictive of benignity. If one or more of these 4 features is identified, no further diagnostic
evaluation is required. If there is doubt on CXR about the presence of these findings, CT should
be performed for better anatomic resolution.
1) nodule calcification on CXR or CT that is either central, diffuse, popcorn or laminar
(concentric rings)
2) fat within a nodule on CT is highly specific for hamartoma
3) a feeding artery and draining vein indicates an arteriovenous malformation
4) a pleural-based opacity with incurving bronchovascular bundles associated with adjacent
pleural thickening or effusion is a characteristic of rounded atelectasis (comet tail sign)
Stability on chest radiographs for two years or more has been considered an indicator of
benignity. This is based on retrospective case series in which surgical resection was performed.
A recent re-evaluation of the original data shows that the two year stability criterion on CXR has
a predictive value of only 65% for benignity, limiting the use of this criterion. 10-20% of small
or subtle lesions interpreted as possible solitary pulmonary nodules on chest radiographs do not
actually represent solitary pulmonary nodules, but lesions in the ribs, pleura, chest wall or
artifacts. When there is doubt about the presence of a nodule on CXR, further imaging is
required.
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Issue 2: What imaging is appropriate?
Summary:
Management strategies for a SPN are highly dependent on the pretest probability of
malignancy. The strategies include observation, resection and biopsy. CT should be the initial
test in most patients with a new radiographically-detected indeterminate SPN. Advances in
technology have improved the ability to differentiate between benign and malignant nodules
using nodule perfusion and metabolic characteristics, as can be evaluated with intravenous
contrast enhanced CT, 18FDG -PET and SPECT.
18
FDG -PET should be selectively used when
the pretest probability and CT probability of malignancy are discordant. If the pretest probability
of malignancy after CT is high, 18FDG -PET is not cost effective. Recommendations for the use
of computed tomography, positron emission tomography, watchful waiting, transthoracic needle
biopsy and surgery in the evaluation of an indeterminate solitary pulmonary nodule are shown in
table 5.
Special Case: Estimating the Probability of Malignancy in Solitary Pulmonary Nodules
Summary
The effectiveness and cost-effectiveness of management strategies for evaluation of SPNs
is highly dependent on the pretest probability of malignancy. Bayesian analysis and multivariate
logistic regression models can be used to predict the likelihood of malignancy for a given nodule,
and perform equal to or better than expert human readers of imaging tests. Using Bayesian
analysis, 18FDG-PET as a single test is a better predictor of malignancy in SPNs than standard
CT criteria.
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Special Case: Solitary Pulmonary Nodule in a Patient with Known Extrapulmonary
Malignancy
A SPN in a patient with an existing extrapulmonary malignancy deserves special
consideration, as they are often detected on staging, follow up chest radiographs or CT. The
etiology of these nodules is important to determine appropriate therapy in differentiating a new
lung cancer from a pulmonary metastasis or nodule of another etiology, such as infection.
In a level 2 (MODERATE EVIDENCE) retrospective study, Quint et al demonstrated
that the likelihood of primary lung malignancy in such nodules depends on the histological
characteristics of the extrapulmonary neoplasm and the patient’s cigarette smoking history. The
medical records of 149 patients with an extrapulmonary malignancy and a solitary pulmonary
nodule at chest CT were reviewed. The histologic characteristics of the nodule were correlated
with the extrapulmonary malignancy, patient age and cigarette smoking history. Patients with
carcinomas of the head and neck, bladder, breast, cervix, bile ducts, esophagus, ovary, prostate,
or stomach were more likely to have primary bronchogenic carcinoma than lung metastasis (ratio
8.3:1 for patients with head and neck cancers; 3.2:1 for all other malignancies combined).
Patients with carcinomas of the salivary glands, adrenal gland, colon, parotid gland, kidney,
thyroid gland, thymus, or uterus had fairly even odds of having bronchogenic carcinoma or
pulmonary metastasis (ratio 1:1.2). Patients with melanoma, sarcoma or testicular carcinoma
were more likely to have a solitary metastasis than bronchogenic carcinoma (ratio 2.5:1). The
results of this study were similar to an earlier study performed by Cahan et al in the pre-CT era.
The authors analyzed thoracotomy results obtained for 35 years in over 800 patients with a
history of cancer, and obtained similar odds ratios for bronchogenic carcinoma versus solitary
pulmonary metastases in different primary malignancies, based on conventional radiographic
detection of the SPN.
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Table 5
Recommendations for the Use of Computed Tomography, Positron Emission Tomography,
Watchful Waiting, Transthoracic Needle biopsy and Surgery in the Evaluation of an
Indeterminate Solitary Pulmonary Nodule. Adapted from [86]
Intervention
CT
18
FDG-PET
Indications
When pretest probability is < 90%
•
•
•
•
Watchful Waiting
•
•
•
•
Percuteanous Transthoracic
Needle Aspiration/Biopsy
•
•
•
Surgery
•
When pretest probability is low (10-50%) and CT results are benign
When pretest probability is high (77-89%) and CT results are benign
When surgical risk is high, pretest probability is low to intermediate (65%)
and CT results are possibly malignant
When CT results suggest a benign cause and the probability of nondiagnostic biopsy is high, or the patient is uncomfortable with a strategy of
watchful waiting
In patients with very small, radiographically indeterminate nodules (<10mm in diameter)
When the pretest probability is very low (<2%) or when pretest probability
is low (<15%) and 18FDG-PET results are negative
When pretest probability is low (<35%) and CT results are benign
When needle biopsy is non-diagnostic in patients who have benign findings
on CT or negative findings on 18FDG-PET
When18FDG -PET results are positive and surgical risk or aversion to the
risk of surgery is high
When pretest probability is low (20-45%) and 18FDG-PET results are
negative
When pretest probability is intermediate (30-70%) and CT results are
benign
When pretest probability is high and CT results are indeterminate (possibly
malignant)
•
When 18FDG -PET results are positive
•
As the initial intervention when pretest probability is very high (> 90%)
Figure 6. Suggested algorithm for clinical management of patients with solitary pulmonary
nodules and average risk of surgical complications
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