161 Elastin in pulmonary pathology dimensional view of a papilla is approximately representing the middle of the threedimensional papillary structure. One would expect that cutting deeper sections from the paraffin block would lead to disappearance of the papillary structure in four to five serial sections (Figure 6). Figure 6. A: cartoon with change of true papillary structure in consecutive series of sections. Note that a true papillary structure (with a radius of about 23 µm) should disappear after 4 – 6 sections. B: Cartoon with cross-section of alveolar wall. Although the shape may change, the cross section can be followed in serial sections. The morphological criteria in the above-mentioned differential diagnosis, i.e. (i) the presence of elastin in alveolar walls, (ii) the absence of elastin in true papillary carcinoma90, and (iii) the three-dimensional size of these papillary mimickers, point to AIS or a lepidic pattern. 12
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