page_title: Lung nodule
section_title: Risk factors
hierarchical_section_title: Lung nodule / Risk factors
caption_attribution_description: English: Original caption: A 51-year-old woman with myelitis transversa presented on CT with a cystic airspace with mural nodule. Axial CT-image in lung window setting shows a subpleural cystic airspace with a mural nodule with somewhat thin, bandlike morphology. The lesion was found suspicious for a lung cancer associated with cystic airspaces. Lobectomy was performed and confirmed the malignant aetiology showing a poorly differentiated adenocarcinoma
context_page_description: 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.
context_section_description: Risk factors for incidentally discovered nodules are mainly:
  General risk factors of lung cancer such as exposure to tobacco smoking or other carcinogens such as asbestos and previously diagnosed cancer, respiratory infections, or chronic obstructive pulmonary disease.
  Size: larger size confers a higher risk of cancer
  Location: Upper lobe location is a risk factor for cancer, while a location close to a fissure or the pleura indicates a benign lymph node, especially if having a triangular shape.
  Margin morphology: a spiculated margin is a risk factor for cancer. Benign causes tend to have a well defined border, whereas lobulated lesions or those with an irregular margin extending into the neighbouring tissue tend to be malignant. In particular, spiculations are highly predictive of malignancy with a positive predictive value up to 90%.  Also, a "notch sign", which is an abrupt indentation of the nodule, increases the risk of cancer, but may also be found in granulomatous diseases.
  Multiplicity: Where the presence of up to an additional 3 nodules has been found to increase the risk of cancer, but decrease in case of 4 or more additional ones, likely because it indicates a previous granulomatous infection rather than cancer.
  Growth rate: solid cancers generally doubles in volume over between 100 and 400 days, while subsolid cancers (generally representing adenocarcinomas) generally doubles in volume over 3 to 5 years. One volume doubling equals approximately a 26% increase in diameter.
  Presence of emphysema and/or fibrosis is a risk factor for cancer. In comparison, the typical size doubling are less than 20 days for infections, and more than 400 days for benign nodules.
  Enhancement: If the exam is done as a combined non-contrast and contrast CT, a solitary nodule with an enhancement off less than 15 Hounsfield units (HU), whereas a higher enhancement indicates a malignant tumor (with a sensitivity estimated at 98%).
  Areas of fatty tissue (−40 to −120 HU) indicates a hamartoma. However, only about 50% of hamartomas are fat containing.
  If there is a central cavity, then a thin wall points to a benign cause whereas a thick wall is associated with malignancy (especially 4 mm or less versus 16 mm or more).
  In case of calcifications, a popcorn-like appearance indicates a hamartoma, which is benign.
  In case of subsolid nodules, being part solid has a higher risk of cancer than being purely ground glass opacity.
  Pleural retraction is far more common in cancers. It is the pulling of visceral pleura towards the nodule.
  A lung nodule abutting a pulmonary cyst is a rare finding, yet indicating cancer.
  Bubble-like lucencies in the nodule indicate cancer:
  Vascular convergence is where vessels converge to a nodule without adjoining or contacting the edge of the nodule, and is mainly seen in peripheral subsolid lung cancers. It reflects angiogenesis.
  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.
caption: Lung nodule abutting a pulmonary cyst.[8]
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