Pulmonary Pathology Online
Pathology of Acute Interstitial Pneumonia (AIP) / Organizing Diffuse Alveolar Damage (DAD)
pneumonitis (AIP), also known as Hamman-Rich syndrome, is a distinct type
of idiopathic interstitial pneumonia affecting patients of both genders
without pre-existing lung diseases.
In 1944 Hamman and Rich described four patients with rapidly progressive respiratory illness of unknown etiology ; all died within six months of presentation and sections from their post mortem lungs showed interstitial fibrosis with areas of hyaline membrane disease.
For these conditions, they introduced the term "acute diffuse interstitial fibrosis of the lung".
In subsequent publications, the eponym Hamman-Rich syndrome has been used to describe cases of diffuse pulmonary fibrosis of chronic nature.
The histological appearances in acute interstitial pneumonitis are those of organizing diffuse alveolar damage and it has also been referred to as "idiopathic ARDS".
Some authors regard AIP being the same as organizing diffuse alveolar damage (DAD).
Katzenstein reserves the term AIP for those cases where there is no identifiable underlying etiology (such as sepsis).
Although acute interstitial pneumonia, is a life-threatening complication following surgery for lung cancer, the cause and risk factors for acute interstitial pneumonia remain unknown.
Microscopic features: This pattern of lung injury is characterized by temporally uniform diffuse interstitial fibrosis of recent onset, with widening of the alveolar septa by prominent fibroblast and myofibroblast proliferation set in edematous stroma, associated with the presence of variable amount of chronic inflammatory cellular infiltration.
Characteristically, there is minimal collagen deposition.
Foci of hyaline membrane, associated with the presence of thrombi within capillaries and small pulmonary arteries are often present.
Prominent alveolar cell hyperplasia and foci of squamous metaplasia may also be present.
The condition can be differentiated from UIP by the lack of the temporal heterogeneity characteristic of the latter, and the absence of honeycomb change and hyalinized collagenous fibrosis.
AIP is a diagnosis of exclusion.
The process is rapidly progressive and carries a high mortality rate up to 70% , despite mechanical ventilation.
It is probably the same condition designated accelerated or rapidly fatal variant of interstitial pneumonitis.
In fatal cases of AIP diagnosis can be based on clinical presentation, radiological, histological and microbiological findings and can be further confirmed by immunohistochemical analysis.
In order to reduce the incidence of acute interstitial pneumonia, it is necessary to perform careful postoperative management for patients who are male, have right lung disease, have undergone preoperative chemo or radiation therapy, or have undergone pneumonectomy.
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