Pulmonary hepatisation refers to the pathologic alteration of lung tissue such that it resembles liver tissue. The term originates as a classic descriptor in surgical pathology, used to describe intermediate stages of lobar pneumonic consolidation.
In imaging, the term is similarly used to describe lung consolidation.
Pathology
According to the classic model, the earliest stage of inflammation in lobar pneumonia is known as congestion. The pulmonary parenchyma is hyperemic, and the small airways are infiltrated with reactive fluid and inciting bacteria.
Subsequently, a normal immunologic response results in recruitment of inflammatory cells and associated hemorrhage, such that the alveoli fill with cellular and fibrinous accumulation. On gross examination, the lung becomes similar in appearance and consistency to liver, and so this is known as red hepatisation.
As the hemorrhage products are resorbed and the exudate within the airways becomes more suppurative, this is known as gray hepatisation reflecting a more white-gray appearance on gross examination.
The final stage of inflammation is known as resolution, where the remaining exudative products are processed by macrophages and fibroblasts 1.
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