ReviewIncidentally detected small pulmonary nodules on CT
Introduction
The chance finding of a lung nodule on a chest radiograph is common, but not overwhelmingly so. However, the widespread availability of multidetector computed tomography (MDCT) imaging has led to a significant increase in the detection of lung nodules. CT shows considerably more nodules than chest radiographs by virtue of its superior spatial and contrast resolution1 and most of these small nodules are of uncertain significance at the time of discovery, and many require further evaluation. The result is an increase in workload for radiology departments, as well as repeated clinic appointments and attendant anxiety for patients. A further consideration is the risks of subsequent non-invasive and invasive diagnostic tests that the detection of a nodule triggers. In the bigger picture there is potentially a significant financial burden to the healthcare system. Not including repeated scans and appointments, in North America surgical resection of a lung nodule is estimated to cost $22,000.2 The issues that surround the characterization of a pulmonary nodule detected incidentally on CT will be reviewed and the appropriateness, and limitations, of recently issued guidelines for the management of pulmonary nodules will be discussed.
Section snippets
Definition
A nodule on CT has been defined as a rounded or irregular opacity that measures up to 3 cm in diameter; a nodule may be solid, part-solid, or non-solid (also known as a ground-glass nodule).3 A parenchymal nodule is separate from the pleural and fissural surfaces of the lung and is completely surrounded by lung. The focus of this article is small parenchymal nodules that measure less than 1 cm in diameter and are incidentally detected on CT of the chest (individuals being screened for lung cancer
Frequency and epidemiology
Estimates of the prevalence of non-calcified pulmonary nodules have been based on lung cancer screening studies, and these have revealed three main points. First, they confirm that nodules are common and are found in selected individuals on 8–51% of CT images at baseline screening.4 Second, nodules are frequently multiple, possibly more often than solitary.1 Third, nodules tend to be less than 10 mm in size (up to 96% of non-calcified nodules are less than 10 mm, of these 72% are less than 5 mm).1
Imaging features of benign nodules
A number of features are reliable, if not infallible, predictors of benignity. Dense, uniform calcification is a strong indicator of benign disease, and was present in 14% of subcentimetre nodules detected at baseline in one lung cancer screening study.5 The presence of calcification can be confirmed by demonstrating a nodule density of greater than 164 HU13 or by simply comparing the density of the nodule with the ribs (a nodule of less than 5 mm in diameter that is uniformly denser than the
Imaging features of near-certain malignant nodules
Even careful assessment of morphology does not usually enable definite differentiation between benign and malignant nodules. In a review of the lung cancer screening literature the frequency of malignancy in nodules with spiculate or lobulate contours varied between 33 and 100%; significantly, however, over 50% of smooth nodules were malignant.4 Thus, the presence or absence of spiculation is of little help in characterization.
The presence of non-solid (ground-glass) components in a nodule
Management strategies
In 2005 the Fleischner Society, an international multidisciplinary body with expertise in respiratory medicine and imaging, published a position statement on the management of small pulmonary nodules. In the absence of many alternatives (e.g., the American College of Chest Physicians guidelines34), the Fleischner Society's recommendations have been widely accepted as current best practice.35 These guidelines distinguish between low-risk individuals (no smoking history and no known risk factors
Limitations of the Fleischner Society guidelines
The Fleischner Society recommendations are undoubtedly valuable in guiding management of indeterminate pulmonary nodules, particularly for inexperienced physicians. However, they do have limitations, for example the common situation of multiple incidental nodules is not fully explored. The presence of a number of nodules in a single patient raises several diagnostic possibilities, for instance multifocal bronchoalveolar cell carcinoma (this accounts for over a quarter of all BAC33), a
Detection and measurement
A radiologist specifically searching for parenchymal nodules only detects about 50% of those present on a CT image.50 Although the majority of missed nodules (less than 5 mm) are very small and, therefore, unlikely to be malignant, there will inevitably be missed cancers. Li et al.51 analysed 39 missed cancers on follow-up imaging that were present on baseline imaging studies. Failure of detection was mostly ascribed to low conspicuity lesions (typically ground-glass or part-solid nodules that
Radiation dose and CT follow-up examinations
Recognition of an incidental pulmonary nodule and the resulting follow-up CT examinations come at the cost of ionizing radiation to the individual. Based on current usage in the UK and USA, it is estimated, but not proven, that CT accounts for 1.5–2% of all cancers.9 In order to minimize these risks, it has been recommended that low-dose CT of the chest should be used in preference to a standard protocol.35 A typical low-dose CT protocol uses a tube potential of 120 kVp or less and a tube
Nodule detection and radiologists' behaviour
Under the auspices of the Society of Thoracic Radiology (USA), international audits in 200064 and 200865 evaluated the recommendations made by thoracic radiologists for the follow-up of “ditzels” (nodules measuring between 3 and 5 mm in diameter) in a number of stereotyped clinical settings. The results show that, in general, radiologists tend to be overly aggressive in follow-up strategies with nearly 50% recommending a follow-up examination in 3–6 months for a ditzel in low-risk individuals.
Non-invasive characterization
The American College of Chest Physicians recommend that, in patients with a low-to-moderate pretest probability of malignancy, 2-[18F]-fluoro-2-deoxy-d-glucose positron-emission tomography (FDG-PET) be used to evaluate indeterminate pulmonary nodules measuring between 8–10 mm.4, 8 Although a recent meta-analysis of 40 studies showed that FDG-PET of non-calcified pulmonary nodules (over 1 cm) was able to demonstrate malignancy with a sensitivity of 96.8% and a specificity of 77.8%, few data are
Definitive characterization
Invasive diagnostic investigations are often necessary for nodules that are indeterminate, or that have features suggestive of malignancy. In these cases, careful consideration of the risk-to-benefit ratio for each patient is necessary and ideally these decisions should be made in a clinico-radiological forum with thoracic surgeons, oncologists, and respiratory physicians present.69, 70 Options available for histological sampling of indeterminate pulmonary nodules include: CT-guided fine-needle
Conclusion
The discovery of an indeterminate pulmonary nodule using CT poses several problems. Management should be determined in a multidisciplinary team setting and take into account the wishes of the patient. The important factors guiding management include the patient's pretest probability of having a malignancy, and imaging features suggestive of either malignancy or benignity. Risks of radiation exposure or more invasive diagnostic procedures must be balanced against the benefit of detecting and
References (78)
- et al.
Early Lung Cancer Action Project: overall design and findings from baseline screening
Lancet
(1999) - et al.
Evidence for the treatment of patients with pulmonary nodules: when is it lung cancer?: ACCP evidence-based clinical practice guidelines (2nd edition)
Chest
(2007) - et al.
Evaluation of patients with pulmonary nodules: when is it lung cancer?: ACCP evidence-based clinical practice guidelines (2nd edition)
Chest
(2007) - et al.
Lung cancer screening using low-dose spiral CT: results of baseline and 1-year follow-up studies
Chest
(2002) - et al.
Screening for lung cancer: the early lung cancer action approach
Lung Cancer
(2002) - et al.
Computed tomography of benign intrapulmonary lymph nodes: retrospective comparison with sarcoma metastases
Mayo Clin Proc
(2002) - et al.
The solitary pulmonary nodule
Chest
(2003) - et al.
Clinical prediction model to characterize pulmonary nodules: validation and added value of 18F-fluorodeoxyglucose positron emission tomography
Chest
(2005) - et al.
A clinical model to estimate the pretest probability of lung cancer in patients with solitary pulmonary nodules
Chest
(2007) The natural history of lung cancer: a review based on rates of tumour growth
Br J Dis Chest
(1979)
Variation in experts' beliefs about lung cancer growth, progression, and prognosis
J Thorac Oncol
Is our natural-history model of lung cancer wrong?
Lancet Oncol
ACR appropriateness criteria on solitary pulmonary nodule
J Am Coll Radiol
PET/CT in non-small cell lung cancer staging-promises and problems
Clin Radiol
How to deal with incidentally detected pulmonary nodules less than 10 mm in size on CT in a healthy person
Lung Cancer
Choices in the management of asymptomatic lung nodules in the elderly
Surg Oncol
CT-guided fine-needle aspiration cytology of solitary pulmonary nodules: a prospective, randomized study of immediate cytologic evaluation
Chest
Transthoracic image-guided biopsy of lung nodules: when is benign really benign?
J Vasc Interv Radiol
Video-assisted thoracoscopic surgery for small indeterminate pulmonary nodules: indications for preoperative marking
Chest
CT-guided agar marking for localization of nonpalpable peripheral pulmonary lesions
Chest
Incidental findings with cardiac CT evaluation: should we read beyond the heart?
Catheter Cardiovasc Interv
Fleischner Society: glossary of terms for thoracic imaging
Radiology
Screening for early lung cancer with low-dose spiral CT: prevalence in 817 asymptomatic smokers
Radiology
Screening for lung cancer with low-dose spiral computed tomography
Am J Respir Crit Care Med
Incidental findings on cardiac multidetector row computed tomography among healthy older adults: prevalence and clinical correlates
Arch Intern Med
CT screening for lung cancer—caveat emptor
Oncologist
Multidetector CT: opportunities, challenges, and concerns associated with scanners with 64 or more detector rows
Radiology
Screening for asymptomatic early bronchogenic carcinoma with low dose CT of the chest
Cancer
Solitary pulmonary nodules: CT assessment
Radiology
The solitary pulmonary nodule
Solitary pulmonary nodules: part I. Morphologic evaluation for differentiation of benign and malignant lesions
RadioGraphics
CT of the solitary pulmonary nodule
AJR Am J Roentgenol
Pulmonary hamartoma: CT findings
Radiology
Solitary pulmonary nodule: high-resolution CT and radiologic–pathologic correlation
Radiology
Small solitary pulmonary nodules (< or = 1 cm) detected at population-based CT screening for lung cancer: reliable high-resolution CT features of benign lesions
AJR Am J Roentgenol
Clustered pulmonary nodules: highly suggestive of benign disease
J Thorac Imaging
Prevalence of pathologically proven intrapulmonary lymph nodes and their appearance on CT
AJR Am J Roentgenol
Ultrasmall intrapulmonary lymph node: usual high-resolution computed tomographic findings with histopathologic correlation
J Comput Assist Tomogr
Thin-section CT features of intrapulmonary lymph nodes
J Comput Assist Tomogr
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