Risk factors for incidentally discovered<unk> s 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 subpleural<unk> . * 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<unk> , increases the risk of cancer, but may also be found in granulomatous diseases. File:CT of a round well-delineated solid<unk>  with smooth border.Round well-delineated solid<unk>  with smooth border. File:CT of a lobulated<unk> .Lobulated<unk> . File:CT of a spiculated<unk> .Spiculated<unk> . File:CT of a<unk>  with a notch sign.A "notch sign". File:CT of perifissural<unk> .A triangular perifissural node can be diagnosed as a benign lymph node. * Multiplicity: Where the presence of up to an additional 3<unk> s 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<unk> s. * Enhancement: If the exam is done as a combined non-contrast and contrast CT, a solitary<unk>  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). File:CT of a fat containing hamartoma.Low attenuating<unk>  (in this case a fat containing hamartoma). File:CT of an aspergilloma.Cavitation with relatively thick wall, in this case aspergilloma). Calcifications and popcorn-like appearance, conferring a diagnosis of hamartoma. * In case of calcifications, a popcorn-like appearance indicates a hamartoma, which is benign. * In case of subsolid<unk> s, being part solid has a higher risk of cancer than being purely ground glass opacity. File:CT of part solid<unk> .Part solid<unk> . File:CT of ground glass<unk> .Ground glass opacity<unk> . * Pleural retraction is far more common in cancers. It is the pulling of visceral pleura towards the<unk> . File:CT of a<unk>  with pleural retraction.Nodule with pleural retraction. File:CT of a subpleural<unk>  with pleural retraction.In this case, pleural retraction is seen as a triangular fat component.<unk>  abutting a pulmonary cyst. * A<unk>  abutting a pulmonary cyst is a rare finding, yet indicating cancer. * Bubble-like lucencies in the<unk>  indicate cancer: File:CT of spiculated<unk>  with bubble-like lucencies.png File:CT of<unk>  with bubble-like lucencies.png Thin slice and maximal intensity projection of a<unk> , the latter better visualizing vascular convergence. * Vascular convergence is where vessels converge to a<unk>  without adjoining or contacting the edge of the<unk> , 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<unk> s, 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.
Lung nodule
Lung abscess
Pulmonary consolidation
Lung tumor
Pleural disease
Mediastinal tumors
Pulmonary infiltrate
Malignant pleural effusion