176 Chapter 14 Figure 1. A, B. Histology of normal expanded alveolar lung parenchyma (left) and iatrogenic collapsed parenchyma (right). Although the patterns are different, samples were taken from the same specimen, with (left) and without (right) transpleural perfusion fixation before submerging fixation. Tumor cells are absent (H&E, 100x). C-F. Two cases of collapsed AIS (adenocarcinoma in situ) are shown (C and D in hematoxylin and eosin (HE) staining; corresponding cytokeratin 7 immunohistochemistry (CK7, IHC) E and F). The case shown in C and E has moderate collapse, with alveolar walls and alveolar spaces that are still recognizable. D and F show an example of prominent collapsed AIS, in which the alveolar walls are compressed against each other and the alveolar “air” space is hardly recognizable. Note I) a regular pattern in both cases and II) collapsed AIS may easily be interpreted as an acinar or papillary pattern The underlying alveolar architecture is distorted by this phenomenon of iatrogenic collapse, which makes it more difficult to evaluate the morphology308. Iatrogenic collapse is more prominent in resection specimen than in biopsies, with usually minimal collapse and open alveolar ‘air’ spaces. In the past, different descriptions were used for ‘collapse’ in pulmonary pathology literature308. In the 1980s, the term ‘collapse’ was used to describe adenocarcinomas with a central ‘scar’ that still showed a recognizable collapsed alveolar framework within condensed elastic tissue on elastin staining 276, 319.
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