Epidemiology

Etiology

Microscopic findings
- Patchy areas of interstitial fibrosis with chronic interstitial inflammation intermixed with normal lung
- Early lesions consist of fibroblastic foci that become increasingly collagenous with time
- Honeycomb pattern with fibrotic walls and cystic spaces lined by bronchiolar epithelium
- Fibrosis most prominent in the subpleural and perilobular regions

Definition: a rare, type of ILD characterized by inflammation of the bronchioles, alveolar ducts, and alveolar walls
Epidemiology
- Incidence: 1–3 per 100,000 hospital admissions
- Affects mostly individuals 40–50 years of age
Diagnostics: histologically characterized by the presence of Masson bodies (granulation tissue buds made of foamy macrophages, mononuclear cells, and fibrous tissue) and chronic patchy interstitial inflammation without fibrosis

General
- All types of ILDs share the same basic pathophysiology.
- Repeated cycles of tissue injury in the lung parenchyma with aberrant wound healing → collagenous fibrosis → remodeling of the pulmonary interstitium
Pneumoconiosis: inhalation of dust particles → phagocytosis by alveolar macrophages → destruction of alveolar macrophages, inflammatory reaction → scarring, granuloma formation

Typical UIP pattern findings
- Honeycombing: multiple cystic lesions within the lung parenchyma due to fibrosis
- Irregular thickening of intralobular septa
- Reticular pattern and mild ground glass opacity (GGO)
- Traction bronchiectasis (irreversible dilatation of the bronchi and bronchioles due to fibrosis)