In another study, correlation of CT and histology indicated that areas that appeared normal by CT showed the exudative phase of alveolar damage with hyaline membranes. The histologic features vary throughout the biopsy, but no normal lung is present. At low power, widened alveolar walls encroach in an irregular way on air spaces, but some alveolar ducts are enlarged because of alveolar collapse. Air spaces are lined by type II cells that show frequent atypia and focal squamous metaplasia. Air spaces contain some blood and scattered inflammatory cells including PMNs.
Granulation tissue is also present in air spaces or bronchioles.
It often becomes epithelialized and incorporated into the interstitium. Hyaline membranes may be seen focally, and acute or organizing thrombi occasionally occur in small to medium-sized arteries. Histologic resolution may occur as in the present patient, or healing with scar may occur. In addition, it is possible, although speculative, that aspiration of gastric contents was the cause of all of the pneumonic and bronchitic problems in this man with a history of gastroesophageal reflux. Aspirative bronchiolitis, which was documented at autopsy, occurred because of the loss of gag reflex that was noted after extubation.