Lung nodule


A lung nodule or pulmonary nodule is a relatively small focal density in the lung. A solitary pulmonary nodule or coin lesion, is a mass in the lung smaller than 3 centimeters in diameter. There may also be multiple nodules.
One or more lung nodules can be an incidental finding found in up to 0.2% of chest X-rays and around 1% of CT scans.
The nodule most commonly represents a benign tumor such as a granuloma or hamartoma, but in around 20% of cases it represents a malignant cancer, especially in older adults and smokers. Conversely, 10 to 20% of patients with lung cancer are diagnosed in this way. If the patient has a history of smoking or the nodule is growing, the possibility of cancer may need to be excluded through further radiological studies and interventions, possibly including surgical resection. The prognosis depends on the underlying condition.

Causes

Not every round spot on a radiological image is a solitary pulmonary nodule: it may be confused with the projection of a structure of the chest wall or skin, such as a nipple, a healing rib fracture or electrocardiographic monitoring.
The most important cause to exclude is any form of lung cancer, including rare forms such as primary pulmonary lymphoma, carcinoid tumor and a solitary metastasis to the lung. Benign tumors in the lung include hamartomas and chondromas.
The most common benign coin lesion is a granuloma, for example due to tuberculosis or a fungal infection, such as Coccidioidomycosis. Other infectious causes include a lung abscess, pneumonia or rarely nocardial infection or worm infection. Lung nodules can also occur in immune disorders, such as rheumatoid arthritis or granulomatosis with polyangiitis, or organizing pneumonia.
A solitary lung nodule can be found to be an arteriovenous malformation, a hematoma or an infarction zone. It may also be caused by bronchial atresia, sequestration, an inhaled foreign body or pleural plaque.

Risk factors

Risk factors for incidentally discovered nodules are mainly:
of a lung nodule, the latter better visualizing vascular convergence.
Air bronchograms is defined as a pattern of air-filled bronchi on a background of airless lung, and may be seen in both benign and malignant nodules, but certain patterns thereof may help in risk stratification.
CT densitometry, measuring absolute attenuation on the Hounsfield scale, has low sensitivity and specificity and is not routinely employed, apart from helping to distinguish solid from ground glass lesions, and to confirm visible fatty areas or calcifications.

Diagnosis

A diagnostic workup can include a variety of scans and biopsies.

Definition

Nodular density is used to distinguish larger lung tumors, smaller infiltrates or masses with other accompanying characteristics. An often used formal radiological definition is the following: a single lesion in the lung completely surrounded by functional lung tissue with a diameter less than 3 cm and without associated pneumonia, atelectasis or lymphadenopathies.

CT scan

For incidentally detected nodules on CT scan, Fleischner Society guidelines are given in table below. For multiple nodes, management is based on the most suspicious node. These guidelines do not apply in lung cancer screening, in patients with immunosuppression, or in patients with known primary cancer.
More frequent CT scans than what is recommended has not been shown to improve outcomes but will increase radiation exposure and the unnecessary health care can be expected to make the patient anxious and uncertain.

PET scan

If there is an intermediate risk of malignancy, further imaging with positron emission tomography is appropriate. It can be done simultaneously as a CT scan in the form of PET-CT. Around 95% of patients with a malignant nodule will have an abnormal PET scan, while around 78% of patients with a benign nodule will look normal on PET. Thus, an abnormal PET scan will reliably pick up cancer, but several other types of nodules will also show up on a PET scan. If the nodule has a diameter of less than one centimeter, PET scans are often avoided because of an increased risk of falsely normal results. Cancerous lesions usually have a high metabolism on PET, as demonstrated by their high uptake of FDG.

Other imaging

Other potential forms of medical imaging of pulmonary nodules include magnetic resonance imaging or single photon emission computed tomography.

Histopathology

For cases suspicious enough to proceed to biopsy, small biopsies can be obtained by core needle or bronchoscopy are commonly used for diagnosis of lung nodules. CT guided percutaneous transthoracic needle biopsies have also proven to be very helpful in the diagnosis of SPN.
In selected cases, nodules can also be sampled through the airways using bronchoscopy or through the chest wall using fine-needle aspiration. Needle aspiration can only retrieve groups of cells for cytology and not a tissue cylinder or biopsy, precluding evaluation of the tissue architecture. Theoretically, this makes the diagnosis of benign conditions more difficult, although rates higher than 90% have been reported. Complications of the latter technique include hemorrhage into the lung and air leak in the pleural space between the lung and the chest wall. However, not all these cases of pneumothorax need treatment with a chest tube.

Excision

Where workup indicates a high risk of cancer, excision can be performed by thoracotomy or video-assisted thoracoscopic surgery, which can also confirm the diagnosis by microscopical examination.

Footnotes