Basic Terminology

BASIC TERMINOLOGY UNDERSTANDING:

The Lungs:  The terms to describe the lung tissue include the parenchyma, interstitium, interstitial or parenchymal all of, which mean the same thing.

Linings:  There are linings to the heart (pericardium), linings to the chest cavity, which includes the mediastinum (parietal pleura) the area that includes the heart, great vessels and other tissues between the lungs) and linings to the lungs themselves (visceral pleura).

Q:  Identify the structures between the heart and the lungs.

 A:  The heart has a lining called the pericardium and the chest cavity, which has the lining called the parietal pleura, also extends along the heart, which is part of the mediastinum.  The lungs have a lining called the visceral pleura thus, the order from inside to outside would be heart, pericardium, parietal pleura overlying the heart and visceral pleura overlying the lung and then the lung.

Further knowledge:  When somebody says that there is a pericardial calcified pleural plaque, this calcified plaque is on the parietal pleural or the lining of the mediastinal portion of the chest cavity, overlying the pericardium or lining of the heart and underlying the visceral pleura or lining of the lung. The plaque does not actually involve the pericardium or lining of the heart, despite its name, but rather the parietal pleura overlying the pericardium.

Pleural plaques as seen in asbestos disease involve the parietal pleura or lining of the chest cavity.  They most commonly occur, either along the sides of the chest cavity known as in-profile plaquing; along the front or back of the chest cavity, known as the face-on (or en-face) plaquing; overlying the diaphragm, known as diaphragmatic plaques; adjacent to the spine, known as paravertebral plaquing or adjacent to the heart, known as pericardial plaquing.   Another term used is that the plaques are circumscribed.

Diffuse Pleural Thickening is a condition, in which sticky fluid gets between the lung and the chest wall.  What happens is that, in most individuals this fluid is resorbed.  However, in some individuals the lining of the lung and the lining of the chest cavity stick together and scar.  Thus, for an elongated distance, there is scarring and thickening of the visceral pleura stuck to the parietal pleura.  Although, some textbooks describe diffuse pleural thickening, as visceral pleural thickening, that is not correct.  What is correct is that the visceral pleura is sticking to the parietal pleura and the two combined are resulting in a scarred thickening, known as diffuse pleural thickening.  When sticky fluid gets in between the lung and the chest cavity, it is actually between the visceral pleural lining of the lung and the parietal pleural lining of the chest cavity.  Such causes of sticky fluid, includes asbestos-caused benign pleural effusions, bleeding from rib fractures, chest trauma or chest surgery, such as bypass or cardiac valve replacement surgery or large infections that break into the chest cavity often with tuberculosis, as a giant pus pocket known as empyemas.  Note that the pleural effusions in congestive heart failure are not sticky and do not result in diffuse pleural thickening.

Diffuse pleural thickening on x-rays causes blunting of the costophrenic angle – the triangular area of lung at the far peripheral lung bases, however, on CT and HRCT, it has been my experience that this does not always have to be the circumstance.  Nonetheless, with diffuse pleural thickening, there can be scars that extend into the lung itself, somewhat like fingers grabbing or pushing/extending into a foam mattress.  These finger-like scars are known as parenchymal bands and if they are large and massive with a wide base, they are known as cicatricial or benign fibrotic masses.  If the finger-like extensions spread out in a fan-like fashion, they can look like a crow’s foot.  If these finger-like extensions grab the lung and fold it in, as if your fingers are folding into the palm of your hand, they will grab the lung and pull it in towards the center of the scar mass, as the finger-like extensions bend downward into the center of the base of the mass. This becomes what is known as rounded atelectasis (atelectasis meaning collapse).  The finger-like extensions are grabbing the lung and forming a rounded collapse of lung centrally within the scar mass.  This can look like it has a comet’s tail of blood vessels and the air tubes, known as bronchioles, extending into the center of this curved in mass of lung tissue.

It is critical that you understand that asbestosis begins most commonly at the posterior bases of the lungs and then later extends to the middle of the lungs and then, with more severe disease into the upper lung zones.  Emphysema from smoking on the other hand, begins in the upper lung zones, greater on the right than the left, extends into the middle lung zones and with severe disease, extends into all six lung zones, to involve the lower lung zones.

Another common term to understand is bronchiolectasis meaning distention of the bronchioles – the small air tubes at the periphery of the lungs.  This occurs when scarring pulls on them, widening their diameters.  Thus, when there is moderate asbestosis, oftentimes, we see little black holes amongst the white scarring, which represent the distended and pulled open bronchioles because of the scarring about them.  In the mild form of asbestosis, this is often not seen.  Honeycombing is a situation, in which the lung tissue is destroyed and all that is left is an empty cavity surrounded by scar material.  Honeycombing commonly occurs in the lower lung zones, but can occur in all six lung zones.  Bullae from emphysema or holes from destruction of the lung caused by smoking are most commonly in the upper lung zones, but can occur in other lung zones, as well.  Honeycombing is usually multi-layered and has scarring about it, whereas bullae that mimic honeycombing are usually due to what is called paraseptal emphysema, forming a single layer of holes and would not be expected to have scar material about them.

The most common cause for nodules in the lungs (rounded densities) would be granulomas, which are scars from prior tuberculosis or fungal infections.  When one gets these from early asymptomatic infections, they fight off the disease and wall of the tuberculous bacilli or the fungal spores forming a rounded scar, known as a granuloma. Lung cancers and metastatic disease (spread of cancer), however, can look similar.

Because of this, when non-calcified or when the calcium deposit is only at the periphery rather than in the center or throughout the nodule, follow-up CT scans are required over time to determine if the nodule grows or changes in size or shape, as would be more likely to occur with either metastasis or a lung cancer.

 

Daniel Powers, M.D.
Diagnostic Radiologist
American Board of Radiology Certified
Federal Government Certified “B-Reader”

 

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