Patterns of Lung Disease - Nodules

Question 1

What are centrilobar nodules?

Answer 1

• Opacification of the centrilobular bronchiole (or less commonly the centrilobular artery) at the center of each secondary pulmonary lobule.
• On CT, multiple small nodules are seen in the centers of secondary pulmonary lobules.
• Never extend to the pleural surface.
• May be solid or of ground glass attenuation, and range in size from tiny up to a centimeter.

Question 2

What causes centrilobar nodules?

Answer 2

• Infectious
  
  • Endobronchial spread of tuberculosis or atypical mycobacteria. Atypical mycobacteria are a diverse spectrum of acid-fast mycobacteria that do not cause tuberculosis. The typical pulmonary manifestation of atypical mycobacteria is a low-grade infection typically seen in elderly women, most commonly caused by Mycobacterium avium-intracellulare.
  • Bronchopneumonia, which is spread of infectious pneumonia via the airways.
  • Atypical pneumonia, especially mycoplasma pneumonia.
• Inflammatory Causes
  
  • HSP (hypersensitivity pneumonitis) is a type III hypersensitivity reaction to an inhaled organic antigen. The subacute phase of HSP is primarily characterized by centrilobular nodules.
  • (CORE only) Hot tub lung is a hypersensitivity reaction to inhaled atypical mycobacteria, with similar imaging to HSP. RB-ILD is an inflammatory reaction to inhaled cigarette smoke mediated by pigmented macrophages.
  • (CORE only) Diffuse panbronchiolitis is a chronic inflammatory disorder characterized by lymphoid hyperplasia in the walls of the respiratory bronchioles resulting in bronchiolectasis. It typically affects patients of Asian descent.
  • (CORE only) Silicosis, an inhalation lung disease that develops in response to inhaled silica particles, is characterized by upper lobe predominant centrilobular and perilymphatic nodules.
  • Respiratory Bronchiolitis Interstitial Lung Disease

Question 3

What are perilymphatic nodules and where are they located?

Answer 3

• Follows the anatomic locations of pulmonary lymphatics, which can be seen in three locations in the lung:
  
  • 1) Subpleural.
  • 2) Peribronchovascular (adjacent to large vessels and bronchi)
  • 3) Septal (within the interlobular septa separating the hexagonal secondary pulmonary lobules).
  • 4) Centrilobular regions

Question 4

DDx for perilymphatic nodules

Answer 4

• Sarcoidosis
  
  • the most common cause of perilymphatic nodules, typically with an upper-lobe distribution.
  • The nodules may become confluent creating the galaxy sign.
    
    • (radiopaedia) The so-called galaxy sign, initially described as the sarcoid galaxy, represents a coalescent granuloma seen in a minority of patients with pulmonary sarcoidosis 1. The same appearance can be seen in tuberculosis 2,3. In other words, it represents a mass-like region composed of numerous smaller granulomas. The appearance of a central core with peripheral nodules is reminiscent of a globular cluster galaxy.
• Pneumoconioses (silicosis and coal workers pneumoconiosis) are reactions to inorganic dust inhalation. The imaging may look identical to sarcoidosis with perilymphatic nodules, but there is usually a history of exposure (e.g. a sandblaster who develops silicosis).
• Lymphangitic carcinomatosis.