Ashley Davidoff MD

• MAP OF STRUCTURE

  • Airways

    • Overview 
      • Acinus
      • Alveolus
      • Cells
      • Carina
      • Bronchi Mainstem
      • Bronchi Segmental
      • Bronchi Subsegmental
      • Small Airways
        • Bronchioles
          • Terminal Bronchiole
          • Respiratory bronchiole
      • Secondary Lobule
      • Trachea
    • Map of Size of Parts of the Lung
    • Right  Lung
    • Left Lung

  • Vessels

    • • Map of the Pulmonary Arteries
        • Pulmonary Arteries
          • Enlarged
          • Normal and Enlarged  (heart module)
          • Enlarged in Pulmonary Stenosis
          • Encasement
      • Bronchial Arteries
      • Venous Drainage
      • Lymphatic Drainage
  • Pleura
    • Pleura

  • Diaphragm

    • Diaphragm

  • Chest Wall

    • Chest Wall

  • Embryology and Growth

    • Embryology and Aging

  • Miscellaneous

    • • • Structural Pathway of Air in the Lungs 
          • with a focus on the histology
        • Mediastinum 
        • Supporting Structures

• FUNCTION

  • Physiology of the Lungs

• MAP OF DISEASES

• DIAGNOSIS

  • MAP of FINDINGS

    • SIGNS IN RADIOLOGY
  •  MODALITIES
    • • CXR
      • CT
• CASE EXAMPLES 
• and the
  • CULTURE and ART Across The Common Vein
  • CULTURAL and ARTISTIC PURSUITS of the AUTHOR Across TCV
    • Art and Culture Related to the Lung
      • Art of the Lung
      • Secondary Lobule Romance – A Story

• Right Lung Parts: Basic Anatomy

   

  The right lung has three lobes: upper, middle, and lower. The lobes are subdivided into segments that are determined by the branching of the main bronchi. The right lung usually has 10 segments subtended by 10 segmental bronchi.  The right upper lobe has three segments called the apical, posterior and anterior segments. The right middle lobe has two segments named the lateral and the medial segments. The right lower lobe has five segments also named according to position; superior, anterior basal, lateral basal, posterior basal, and medial basal segments.   The superior segmental bronchus is the first branch of the RLL system and it is directed posteriorly.  The superior segment is vulnerable in the supine patient who aspirates because of its posterior position.   

   

  

   

  The superior segment occupies the entire upper portion of the lower lobe. It sits atop the remaining four segments of the right lung: the anterior basal, lateral basal, posterior basal and medial basal segments. These basal segments form the base of the almost pyramidal shaped lower lobe as well as the base of the lung it and them rest upon the diaphragm.

  

  Right Lung Parts: Applied

  It is essential to know and understand the distribution of the lobes for accurate assessment of the CXR.  For example, a disease process in the upper lung field on the right does not necessarily mean that the disease is in the RUL.  Since the RLL is so large and extends almost the entire thoracic distance (see image 3a), it is difficult to localize on the P-A exam of the chest.  However, if one reviews the lateral exam, the distinction between right upper and right lower lobe is much easier, since the lower lobe is mostly posterior and below the fissure, and the upper lobe mostly anterior and above the fissure. 

  

  

  

  

   

  The following images in P-A and lateral projection reveal the large posteriorly positioned right lower lobe (RLL).  Note how much larger the RLL is compared to the RML and the RUL.

  

  

  The major fissure is the dividing line between the RLL on the one hand and the RUL and RML on the other.  The minor fissure, also known as the transverse fissure, divides the RUL from the RML and is easily perceived on the lateral examination.

  

  

  

  

  Sometimes there is an extra lobe in the right upper lung field called the azygous lobe and the azygous vein runs in the accessory fissure.   The azygous lobe is an accessory lobe in the apex of the right lung that is found in approximately 0.5% of routine chest x-rays.  It is recognized by a fissure in the apex that has an inverted comma shape.

  The following diagram demonstrates the cross sectional appearance of the right lung at the level where both the major and minor fissures are seen.  It correlates the CTscan with the anatomical specimen.

  

  

  

   

• Left Lung Parts: Basic Anatomy     The left and right lungs are very different.  We have already noted that the mainstem bronchi are different, with the left mainstem bronchus being long and thin, while the right mainstem bronchus is short and fat.  The left lung has only two lobes.  There is a left upper lobe (LUL) and a left lower lobe (LLL).  The left lung does not have a middle lobe.  Instead, the middle lobe equivalent is the lingula, which is in fact part of the LUL and not a separate lobe.    The two lobes of the left lung are separated by the major or oblique fissure, which is the only fissure on the left side. The left lung is smaller than the right and has 8 segments compared to the 10 segments on the right.     The upper lobe of the left lung has superior and lingula divisions. Both of these divisions have two segments each. The segments of the superior division are the apical-posterior and the anterior segments. The lingula is divided into superior and inferior segments. As noted there is no fissure between the upper segments of the LUL and the lingula – they are both part of the LUL.  The division of the lower lobe closely resembles that of the right except that there is consolidation of two of the left lower lobe segments.  Thus while the RLL has 5 segments the LLL has only four.  Again, as is characteristic, the left lung consolidates its component parts.     The superior segment of the LLL forms the top of the pyramid of the LLL.  Inferiorly and at the base of this pyramid, the anterior and medial segments combine to form the anteromedial basal segment, followed by the lateral basal, and posterior basal segments. 

  

  Left Lung Parts: Applied

   

  The overall volume of the left lung is smaller than the right, but the distribution of volume between LUL and LLL is more equalized and balanced.  Again in the P-A projection the two lobes overlap each other.  A nodule in the upper lung field or lower lung field as seen on the P-A projection can be located either in the upper or lower lobe.  The lateral examination is essential to accurately locate the disease.  The LUL is anterior and above the fissure (see Fig 1b), while the LLL is posterior and below the fissure (see Fig 2b).

  

  

  

  

  

  

   

  

  

   

  

  

  

  

   

  

   

  When we read plain films of the chest we use the position and relations of the lungs to the heart and the fissures to locate disease processes, including infiltrates, nodules, and regions of atelectasis.  We use two principles to locate disease.  The first is the described relations of structures to each other, and the second is the concept of “silhouetting.”  The important facts that pertain are that the RML abuts the right heart border, the lingula the left heart border, and the lower lobes on both sides abut the diaphragm.  The principle of “silhouetting” is commonly used to define the nature and location of a soft tissue process in the lung.  We have described the fact that we are able to see and distinguish two different structures because their densities are different.  Thus we are able to see the heart border or the diaphragm, for example, because they abut air- filled lung tissue which has a completely different density to their soft tissue nature.  If, however, the ai- filled lung is replaced by pus or exudates (pneumonia) or become airless (atelectasis), then the abutting structures both have soft tissue density and cannot be distinguished from one another.  If there is a process that silhouettes the right heart border in the P-A projection then we know that this process is in the RML.  Similarly, if the left heart border cannot be distinguished from the disease process, we know that it is in the lingula.

  It is important to identify accurately the location of disease, particularly nodules and masses which may have to be surgically removed, since the surgeon has to know which part of the lung has to be removed.