Table 1.

Definition of histopathological criteria for different types of pneumonia

Types of pneumonia	Features
Suppurative bronchopneumonia (SBP)	The exudate predominantly composed of neutrophils within the lumen of bronchi, bronchioles and alveoli with hyperaemia, cellular debris or hyperplasia of BALT or fibrosis
Fibrinous bronchopneumonia (FBP)	The exudate predominantly composed of fibrin within the lumen of bronchi, bronchioles and alveoli with oedema of inter‐lobular septa or coagulative necrosis or fibrosis
Interstitial pneumonia (IP)	Thickening of the alveolar septum by oedema, congestion or hypercellularity or hyperplasia of type II pneumocytes with hyaline membranes, interstitial fibrosis or BALT hyperplasia
Bronchointerstitial pneumonia (BIP)	The presence of features of both bronchiolar necrosis and IP
Bronchopneumonia + bronchointerstitial pneumonia (BP&BIP)	The presence of features of both BP (SBP or FBP) and BIP
Bronchiolitis	Necrosis of epithelial cells in bronchi or bronchioles with purulent or fibrinous exudates or accumulation of inflammatory cells, epithelial hyperplasia (squamous metaplasia)

Abbreviation: BALT, bronchus‐associated lymphoid tissue.

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