Opacity

Mass vs. Infiltrate

 

 

    The basic diagnostic instance is to detect an abnormality.  In both of the cases above, there is an abnormal opacity.  It is most useful to state the diagnostic findings as specifically as possible, then try to put these together and construct a useful differential diagnosis using the clinical information to order it.

    In each of the cases above, there is an abnormal opacity in the left upper lobe.  In the case on the left, the opacity would best be described as a mass because it is well-defined.  The case on the right has an opacity that is poorly defined.  This is airspace disease such as pneumonia.

Mass Location

Intraparenchymal vs. pleural vs. extrapleural

 

This diagram shows three locations that a mass can exist in the thoracic cavity.  

A = intraparenchymal B = pleuralC = extrapleural

 

CT showing a mass that is likely pleural based (red arrow).  Note the pleural effusion posteriorly.

Another CT showing bone destruction indicative of an extrapleural mass.

Lobes and Fissures

On the PA chest xray, the minor fissure divides the right middle lobe from the right upper lobe and is sometimes not well seen. There is no minor fissure on the left. The major fissures are usually not well seen on the PA view because you are looking through them obliquely. If there is fluid in the fissure, it is occasionally manifested as a density at the lower lateral margin.

The left image shows the right minor fissure (A) and the inferior borders (B) of the major fissures bilaterally.  The right image shows the superior border of the major fissures (B) bilaterally.

 

On the lateral view, both lungs are superimposed. Think about them separately, the left lung has only a major fissure as shown.  

The right lung will have both the major and minor fissure.

 

 

The patient above has a pleural effusion extending into the fissure.  Which fissure is which?  What is the bright loop near the center of the films?

(Click each image for answers)

 

 

 On a CT scan the fissures are shown as an area of paucity of vessels in the region of the capillaries near the fissure. If a very thin slice is taken, the pleura can actually be seen as a line (arrows).

Mediastinum and Lungs

The radiologist needs to know both the structures within the mediastinum forming the mediastinal margins and the lobes of the lungs forming the margins of the lungs along the mediastinum and chest wall. If a mass or pneumonia "silhouettes" (obscures) a part of the lung/mediastinal margin, the radiologist should be able to identify what part of the lung and what organ within the mediastinum are involved. The margins of the mediastinum are made up of the structures shown below. Trace the margin of the mediastinum with your eye all the way around the margin.  Think of the mediastinal structures that comprise this interface.  If the margin were abnormal you could diagnose the cause.

 

This image outlines the specific anatomy of the PA chest x-ray.

 

This image indicates the locations of each lung margin on chest x-ray.

 

 

Trace the margin of the lung with your eye in the image below thinking about what mediastinal structure and what lobe of the lung is present at this margin.

Bronchi

 

A physician should absolutely know the anatomy of the bronchi. Look at the drawing on the left and compare it to the chest x-ray on the right. You can see that the major bronchi are visible if you look carefully. It may be beneficial to practice drawing the bronchi and labeling them until you are entirely familiar with their names and locations. The table below shows the segmental bronchi and their designated numbers.

A = Right Main Stem BronchusB = Right Upper Lobe Bronchus  B1 = Apical Segmental Bronchus  B2 = Anterior Segmental Bronchus  B3 = Posterior Segmental BronchusC = Bronchus IntermediusD = Right Middle Lobe Bronchus  D4 = Lateral Segmental Bronchus  D5 = Medial Segmental BronchusE = Right Lower Lobe Bronchus  E6 = Superior Segmental Bronchus  E7 = Medial Basal Segmental Bronchus  E8 = Anterior Basal Segmental Bronchus  E9 = Lateral Basal Segmental Bronchus  E10 = Posterior Basal Segmental BronchusF = Left Main Stem BronchusG = Left Upper Lobe Bronchus  G1, G2 = Apicoposterior Segmental Bronchus  G3 = Anterior Segmental BronchusH = Lingular Bronchus  H4 = Superior Lingular Segmental Bronchus  H5 = Inferior Lingular Segmental BronchusI = Left Lower Lobe Bronchus  I6 = Superior Segmental Bronchus  I7 = Medial Basal Segmental Bronchus  I8 = Anterior Basal Segmental Bronchus  I9 = Lateral Basal Segmental Bronchus  I10 = Posterior Basal Segmental Bronchus

SMALP = "Suppose My Aunt Loves Peaches" is a helpful way to remember the segmental lower lobe bronchi.

Pulmonary Vasculature

The following drawings show the major pulmonary vessels within the mediastinum.  The bronchi that you have already learned are the same as on the prior drawing.  These structures are obviously present on every chest x-ray but are usually unrecognized.  If you learn the location of these structures, this will help you understand the anatomy as shown on chest x-rays and chest CT.

 A drawing representing the pulmonary vasculature.

 

The following schematic drawing should help you sort out these structures.  After the bronchi, remember that the left pulmonary artery arches over the left upper lobe bronchus and the right

pulmonary artery passes posterior to the ascending aorta to divide into the truncus anterior and the descending RPA.  Note that except in the right upper lobe, the pulmonary veins are generally

anterior to the pulmonary arteries.

A = Apical segmental bronchusB = Posterior segmental bronchusC = Anterior segmental bronchusD = Bronchus intermediusE = Truncus anteriorF = CarinaG = Right main pulmonary arteryH = Left main pulmonary arteryI =  Right inferior pulmonary arteryJ = Right superior pulmonary veinK = Right middle lobe bronchusL = Right lower lobe bronchusM = Right inferior pulmonary veinN = Left AtriumO = Left superior pulmonary veinP = Apicoposterior segmental bronchusQ = Left upper lobe bronchusR = Lingular bronchusS = Left inferior pulmonary arteryT = Left inferior pulmonary vein

 

Left, left pulmonary artery on CT.  Right, right pulmonary artery on CT.  Note how the left pulmonary artery passes over the left mainstem bronchus to descend behind it, while the RPA passes behind the ascending

aorta.