SOLITARY NODULE OF THE LUNG - RESPIRATORY-HEALTH

What is a Solitary Nodule of the Lung?

Solitary nodules of the lung (NPS), also called "coin lesion" by the Anglo-Saxons, are rounded lesions that do not exceed 3 cm in diameter, completely surrounded by normal lung parenchyma, without other associated anomalies.

Formations larger than 3 cm are more properly called masses and are often malignant in nature.

Index Article

Incidence

Solitary lung nodules can be found randomly during imaging tests of the neck, upper limbs, chest, abdomen, and are described in approximately 0.9-2% of all chest radiographs. .

The diffusion of computed tomography (CT), a method characterized by a higher resolution capacity than radiography, has led to an increase in the frequency of detection of these nodules.

In a study conducted using CT scans for lung cancer screening in patients at risk, lung nodules greater than 5 mm in diameter were described in 13% of patients at initial evaluation. In another study, which involved performing total body CT in adults, pulmonary nodules were described in 14.8% of the examinations; however, this percentage also included nodules with a diameter of less than 5 mm. , the estimated prevalence of solitary lung nodules would be included, according to the various studies available in the literature, between 8% and 51% (6.7).
The American College of Chest Physicians (ACCP) does not recommend screening for lung cancer in the general population or among smokers; in fact, the execution of these tests has not so far been found to be able to obtain a decrease in mortality rates. The rational basis of the indication to subject the lesions identified randomly to close monitoring reside in the fact that the diagnosis and treatment of early stage lung cancer are able to obtain more favorable overall outcomes.

Characterization of the nodules

A solitary lung lump can be attributed to several causes. The first step in the clinical evaluation of these lesions aims to define their benignity or malignancy. The most common benign etiologies include infectious granulomas and hematomas, while the most frequent malignant etiologies include primary lung cancers, carcinoid tumors, lung metastases.
Some radiologically determinable features of the nodule, such as shape and rate of growth, are often useful in defining the likelihood of a malignant lesion.
An analysis conducted on the results collected from 7 different studies compared the size of the nodule and the frequency of malignant lesions: lesions with a diameter of less than 5 mm, a diameter between 5 mm and 1 cm, and a diameter greater than 2 cm , respectively, presented malignancy rates lower than 1%, between 6% and 28%, and between 64 and 82%.
The morphological characteristics of the nodule related to the rate of malignancy include the density of the lesion, its margins and the presence or absence of calcifications. In general terms, dense, “solid”-looking lesions are less frequently malignant than lesions with “ground glass” opacity. Another study showed that the presence of irregular margins is associated with a 4-fold increase in the likelihood of a malignant lesion; benign nodules are in fact generally characterized by regular and well-defined margins. The presence of calcifications is generally considered a sign of benignity, especially in the presence of patterns that radiologists describe as "concentric", "central", "similar to popcorn", "homogeneous".
Growth rate can also be helpful in determining the likelihood of lump malignancy. Malignant lesions typically have a doubling time of between one month and one year; therefore, a lump that has remained stable in size for more than 1-2 years is more likely to be benign. It should be remembered that for spherical masses an increase of 30% in the diameter corresponds to a doubling of the volume. Although masses with rapid volumetric doubling time (ie less than one month) are less frequently malignant, these masses also need to be carefully evaluated in order to define their etiology, and consequently treatment.
However, there are numerous limitations in the measurement of the size of a nodule: inflammatory changes in the periphery or scars and compression zones of the parenchyma can lead to overestimation of growth, while the occurrence of hemorrhages, necrosis or cavitations can produce errors of different sign; even the partial volume effect can overestimate the size of a nodule, especially if thin layers are not used. It is not always easy to decide the size of the diameter; this must be as accurate as possible, and must be obtained by calculating the average of at least two dimensions in two serial images.However, measurements based on diameter or section area may not be able to distinguish between benign growth and malignant growth, as this may be asymmetrical in the three dimensions of the space; for this, and due to the poor capacity of the "human eye to perceive the growth of a nodule when it is subcentimeter in size, the need to recognize volumetric measurement techniques is suggested, although some authors, through complex comparisons with" phantoms ", ensure that a serial control with CT to a interval less than doubling time (1 month) can recognize growth even in small subcentimeter nodules.
The dimensional stability of solid nodules for two years has been indicated as a criterion of benignity, also not absolute, as nodules with very slow growth (doubling time> 700 days) may appear stable on observation after 2 years.
Dynamic CT with enhancement after CD is, in the field of diagnostic imaging, the test that provided the best sensitivity in the study of the pulmonary nodule (sensitivity from 98% to 100%; specificity from 29% to 93%), definitely orienting towards a judgment of benignity when the "density increase after contrast medium is less than 15-20 HU. MRI showed similar sensitivity, but greater specificity than CT.