Small airways disease

Small airways disease comprise of a group infectious as well as non-infectious conditions that affect the small airways (i.e. airways that are more peripheral to the main bronchi and proximal bronchioles (4^th the 14^th generation) - arbitrarily considered to be those with an internal diameter of ≤2 mm ³).

Pathology

While some authors consider this term synonymous with a bronchiolitis ⁴, conditions such as asthma may also fall under this group ⁷. There are also many other conditions that can affect or be associated with small airways which include:

• hypersensitivity pneumonitis ³

• sarcoidosis - pulmonary manifestations of sarcoidosis ³

• respiratory bronchiolitis interstitial lung disease ³

• micro carcinoid tumourlets - diffuse idiopathic pulmonary neuroendocrine hyperplasia  ³

• follicular bronchiolitis ³

• drug-induced small airways disease

• COVID-19 infection - usually as a delayed / late sequelae ^12,13

• connective tissues diseases

  • rheumatoid arthritis ¹¹

  • pulmonary manifestations of inflammatory bowel disease ¹¹

  • Sjogren syndrome ^9-10

Radiographic features

CT

There are many CT features associated with small airways disease, which include:

• direct signs

  • thickened peripheral airways: may only be seen in the proximal portion

• indirect signs (many of these features may be nonspecific on their own):

  • air trapping ⁷

  • subsegmental atelectasis ⁷

  • mosaic lung attenuation ¹

  • centrilobular nodules ¹ 

  • tree-in-bud changes ^1,8