Abstract

Theresa C McLoud
Department of Radiology, Massachusetts General Hospital, USA

Idiopathic interstitial pneumonias are a group of disorders that were originally described by Dr. Averill Liebow in the mid 1970’s. These interstitial pneumonias have undergone a revision of classification and include the following entities:

1. Usual interstitial pneumonia (idiopathic pulmonary fibrosis)
2. Respiratory bronchiolitis – associated interstitial lung disease
3. Desquamatic interstitial pneumonitis
4. Acute interstitial pneumonitis (Hammon Rich)
5. Cryptogenic organizing pneumonia (BOOP)
6. Nonspecific interstitial pneumonia (NSIP)

Usual interstitial pneumonitis (UIP)
This is the histologic counterpart of idiopathic pulmonary fibrosis. High resolution CT findings include reticular opacities and honeycombing in a very striking peripheral and lower lobe distribution. These may be associated with traction bronchiectasis and architectural distortion.

Respiratory Bronchiolitis-Associated Interstitial Lung Disease (RB-ILD) and Desquamative Interstitial Pneumonia (DIP)
These two entities represent a spectrum of smoking related fibrotic and inflammatory reactions. In RB-ILD typical findings on HRCT include centrilobular nodules, which are usually of ground glass opacity with an upper lobe predilection. DIP is now considered to be a more extensive form of respiratory bronchiolitis. Typical HRCT findings are that of ground glass opacities in a peripheral and lower lobe distribution.

Acute Interstitial Pneumonia (AIP)
This is a rapidly progressive process with a 2-3 week presentation. The histiologic pattern is indistinguishable from adult respiratory distress syndrome. High resolution CT will reveal patchy areas of ground glass opacity and consolidation with focal areas of sparing.

Crytogenic Organizing Pneumonia (COP & BOOP)
This entity was originally described as BOOP. High resolution CT findings show areas of consolidation with a peribronchovascular distribution. Some cases may exhibit a peripheral subpleural location of opacities.

Nonspecific Interstitial Pneumonia (NSIP)
This entity was described in the 1980’s. Many patients have underlying collagen vascular disease. It is a form of slowly progressive fibrosis. On CT, there is usually a lower lobe predominance with reticulation and traction bronchiectasis but seldom honeycombing.