Circumscribed parenchymal lesions that measure less than 3-4 cm. in diameter and are completely surrounded by aerated lung.
Most nodules are asymptomatic and approximately half prove to be malignant.
Pulmonary nodules identified in approximately 1.6 million people per year in the US and are seen on approximately 30% of CT images of the chest.
250,0000 discovered per year, and 80,000. are significant enough to warrant surgery.
A review of CT screening lung cancer trials noted that a lung nodule was detected in up to 51% of study participants.
More than 95% detected nodules are benign and have a wide variety of causes, including infections granulomatous disease, hamartomas, AV malformation, round atelectasis, and lymph nodes.
Small nodules are less than 1 cm in size, and nodules 3 cm of greater is considered to be a mass.
It is important to identify nodules as diffuse or focal, is the distribution central or peripheral, are they located in the upper lobes, or lower lobes, and to understand the relationship between nodule and the secondary pulmonary lobule the most basic anatomical unit of the lung, which includes centrilobular structures, and peripheral structures
Small nodules can be described as centrilobular, perilymphatic, or randomly distributed.
Important features of a pulmonary nodule include size, whether they are solid, or subsolid, whether they are cavitated, whether calcification is present, and the appearance of the edges of spiculated, smooth, or with a halo.
Large randomly distributed nodules are characteristic of cancer or infection.
The halo sign can occur with cancer and infections, as well as disorders, including vasculitis, sarcoidosis, and inflammatory bowel disease.
Estimated hundreds of thousands of pulmonary nodules are detected each year, and more will be found due to the US Preventive Services Task Force recommendation of annual CT lung cancer screening among high-risk individuals.
Differential diagnosis for pulmonary nodules includes:malignancy, infections, granulomas, benign tumors, and inflammatory nodules.
The risk of a solid nodule being malignant is based on its size, characteristics, margins, presence of calcification, growth rate, and patient risk factors.
High-risk lung nodules are defined as nodules with an estimated cancer risk of at least 65%.
More than 50% of patients with a pulmonary nodule have more than one nodule.
Most pulmonary nodules are not malignant, but evaluation entails radiographic surveillance, and some patients undergo invasive procedures such as biopsy and/or surgical resection.
Approximately 95% of all pulmonary nodules identified on CT scans are benign.
A dominant pulmonary nodule refers to the largest or the most suspicious appearing nodule.
Solid pulmonary nodules smaller than 6 mm found incidentally on CT scans do not require follow-up imaging in low-risk patients: optional follow-up imaging can be considered in high-risk patients.
The incidence of a pulmonary nodule increases with age from 0.4 per 1000 person-years in people age 18 to 24 to 20.3 per thousand person-years in those age 85 to 89 years.
Lung nodules in the presence of radiographic emphysema is associated with a 3.3 fold relative risk of malignancy in an incidentally discovered pulmonary nodule compared with age and smoking matched controls.
The risk of cancer in a solid nodule smaller than 6 mm is less than 1%.
Surveillance tends to prolong uncertainty, increase anxiety, increases radiation exposure, and invasive testing can cause significant complications.
Malignant risk factors include age, smoking history, personal history of cancer, history of lung cancer in the first degree relative, environmental exposure to asbestos or radon.
Low risk nodules corresponds to an estimated risk of cancer of less than 5% and is associated with young age, less smoking, smaller nodule size, regular margins, and location in area other than the upper lobe.
High risk of greater than 65% for cancer is associated with older age, heavy smoking, larger nodule size, irregular or spiculated margins and upper lobe location.
Intermediate risk nodules have mixed low and high risk characteristics which may include other high risk factors such as emphysema and pulmonary fibrosis, positive family history, and known exposure to inhale carcinogens.
Large, randomly distributed, nodules, and effusion, can occur in patients with synchronous, lung, cancers, metastatic, disease, and pulmonary lymphoma.
Lung nodules may result from malignancy, infections, inflammatory disorders, vascular abnormalities, and congenital abnormalities.
Viral, bacterial and fungal infections in the lungs can all cause nodules.
Small vessel vasculitis, either anti-neutrophil cytoplasm antibody associated vasculitis or immune complex mediated vasculitis can be associated with pulmonary nodules.
Connective tissue disorders, such as rheumatoid arthritis, Sjogren’s syndrome, systemic lupus, polymyositis, dermatomyositis and mixed connective tissue disease can cause pulmonary nodules.
80% of small, solid lung nodules are classified as benign granulomas or intrapulmonary lymph nodes.
Granulomas may resolve or undergo fibrosis and form a scar.
Pulmonary hamartomas account for 10% of benign, solid pulmonary nodules.
Vascular nodules include arteriovenous malformations, pulmonary infarcts, pulmonary varices, and pulmonary artery aneurysms.
Other nodules include intrapulmonary lymph nodes, rounded atelectasis, bronchogenic cysts, and mucoid impaction.
The sensitivity for detecting malignant pulmonary lesions of any size range from 83-100%.
CT-PET scan identifies a metabolically active lesion.
CT-PET scan negativity does not exclude malignancy as many slow growing tumors, such as adenocarcinoma and carcinoid tumors, have no standard uptake value.
After detection, the management of most noncalcified nodules includes a follow-up for two years to establish stability and that no increase in size or change in shape or appearance.
The American College of Chest Physicians guidelines recommend limiting surveillance to two years for most patients.
It is recommended that patients at lower risk of cancer such as non-smokers or those with small nodules should receive fewer tests.
Solid nodules less than 6 mm do not require routine follow-up in low-risk patients.
For pure ground glass nodules less than 6 mm no routine follow-up is recommended.
Some solid nodule is less than 6 mm with suspicious morphology, upper lobe location, or both may have a higher risk and warrant follow up at 12 months.
For solitary solid non-calcified nodules measuring 6-8 mm in patients at high risk, an initial follow-up examination is recommended 6-12 months and again and 18-24 months.
For solitary solid non-calcified nodules greater than 8 mm in diameter, three month follow-up is considered, work up with combined PET and CT scan, tissue sampling or a combination thereof.
The most common cancers that result in metastatic pulmonary nodules, include lung cancer, originating in another part of the lung, colorectal, cancer, renal, carcinoma, pancreatic carcinoma, breast, cancer, and testicular cancer.
Less common cancers, that predominantly metastasize to the lung include: choriocarcinoma, Ewings, sarcoma, melanoma, osteosarcoma, and thyroid cancer.