Pulmonary interstitial oedema

Pulmonary interstitial oedema represents a form of pulmonary oedema resulting from pathological fluid buildup in the interstitial spaces due to increased hydrostatic driving pressure.

Pathology

Interstitial lung oedema arises almost exclusively due to an increase of the pulmonary capillary hydrostatic pressure (P_cap), which occurs most commonly in left sided heart failure, hence it is a key element of cardiogenic lung oedema. The increased P_cap leads to an excess filtrate filling the bronchovascular interstitium (causing the imaging appearance of peribronchial cuffing and septal thickening), and lymphatic distension (manifesting as the eponymous Kerley B lines on plain film). Interstitial oedema can quickly progress into an alveolar pattern, where the alveolar spaces became flooded too ¹.