A pulmonary nodule is a well-defined opacity surrounded by lung parenchyma measuring less than 3cm (greater than 3cm is a lung mass). Pulmonary nodules are classified as solid or subsolid. Subsolid nodules are subclassified into pure ground glass and part solid nodules.
Peripheral lung nodules may represent early lung cancer hence are an opportunity for cure.
Risk assessment: patient and the scan
Lung nodules are asymptomatic and often detected incidentally on CT chest and non-lung CT scans performed for other reasons. Nodule assessment on non-lung CTs has limitations. Confirmation with a dedicated CT chest is favourable.
Nodule risk assessment for lung cancer depends on several factors. Clinical factors include age, family history of lung cancer and other cancers, asbestos exposure, and cigarette smoking. Absence of a smoking history does not exclude lung cancer.
Radiological characteristics such as size, shape, spiculation, effect on adjacent pulmonary architecture and background emphysema need to be interpreted. Peri-fissural nodules represent intrapulmonary lymph nodes and are usually benign although there are exceptions. Presence of mediastinal or hilar lymphadenopathy indicates urgent assessment irrespective of the nodule size.
Lung nodules are best evaluated on thin (</=1mm) slice CT reconstruction. There are limitations in comparing two scans with different slice thickness, a dedicated CT chest versus a non-lung CT and even CT chests done on different machines. Comparison with previous CT imaging is an important initial step during nodule assessment. Availability of prior imaging at the time of reporting adds value for the reporting radiologist and the clinician.
Identifying the clinical context at the time of CT chest scan is paramount. If there are features of infection, then an inflammatory nodule is likely and may resolve at short term interval follow up CT. Alternatively, if detected on a screening CT chest, the malignancy risk is higher.
There are several risk assessment scores used to determine the malignancy risk of a lung nodule. Nodule management strategy depends on the risk, and this is currently being investigated in a prospective clinical trial. In general nodules are termed as low, intermediate, or high risk.
Management
Patient involvement in decision making is important for good outcomes. Management options include surveillance or diagnostic intervention.
For high-risk nodules greater than 1cm, presence of spiculation or thoracic lymphadenopathy, immediate specialist assessment is necessary.
A FDG PET scan is useful for identifying occult extra-thoracic metastasis and thoracic nodal metastasis. There is a not-insignificant false negative rate for thoracic nodal disease on PET (PET occult thoracic lymph nodal metastasis) as well as a false PET positive thoracic lymph node (non-malignant PET positive lymph nodes from anthrasilicosis or granulomatous infections).
Tissue confirmation of thoracic lymph node status with linear endobronchial ultrasound (EBUS) bronchoscopy is recommended for all lung nodules proven or suspicious for lung cancer when they are within the inner two thirds of the lung fields, associated with abnormal thoracic lymph nodes on CT chest or PET and when the lung nodule is not PET avid. Adenocarcinomas and intensely FDG avid lung cancers also carry a higher risk of occult nodal metastasis and tissue confirmation of nodal status is advantageous.
Biopsy of the peripheral lung nodule can be performed at the same bronchoscopy by using a radial EBUS probe if the lymph nodes are non-malignant at onsite examination (Image A). EBUS bronchoscopy has an excellent safety profile. Alternatively, the nodule can be biopsied by CT guidance as a separate procedure.
For intermediate risk nodules, the options depend on the clinical circumstance, patient preference and risks of diagnostic biopsy. When there is a history of infective symptoms at presentation when initial CT was done, then a short-term interval CT scan can be done in six weeks to three months with antibiotic treatment assessing for temporal behaviour. Inflammatory nodules usually reduce in size or resolve on follow-up scan.
A persistent nodule is concerning and an enlarging nodule highly suspicious for malignancy. If a nodule is persistent but stable in size and shape, radiological surveillance with CT scans for 24 months for solid nodules and up to five years for ground glass/part solid nodules is a reasonable approach. Alternatively, evaluation with a FDG PET and proceeding to a biopsy is acceptable.
For a nodule deemed low risk, surveillance is favoured.
Managing patient anxiety around the detection of a lung nodule and consideration of their preferences during assessment is helpful in achieving good outcomes. Work up also includes lung function testing and assessing fitness for surgery since treatment options for early-stage lung cancer are lobar or sub-lobar surgical resection or for non-surgical candidates, stereotactic body radiation therapy. This is often recommended following an MDT discussion.
Key messages
- Lung nodules are an opportunity to cure lung cancers
- Nodule malignancy risk stratification determines management
- FDG PET is indicated for detecting distant metastasis and not very useful in determining nodule malignancy risk.