68 Chapter 5 with adjacent uninvolved areas. Inspection of the lung during collapse may reveal a focally elevated pleural surface. This finding may help the surgeon identify the location of the underlying lesion and guide clamp and staple gun placement. This observation may be especially useful in cases of small nonpalpable lesions. Surgical collapse of peripheral lung leads to approximation of the alveolar walls, possibly providing the impression of increased cellularity and more extracellular matrix. This pitfall should not be confused with interstitial fibrosis89. This artifact can be highlighted with immunohistochemical staining for CK (cytokeratin) (eg, CK 7) and endothelium markers (e.g., CD31), or with an elastic stain. Peripheral lung collapse may give rise to 3 pitfalls in the diagnosis of adenocarcinoma. First, depending on the amount of diminished air, the collapsed alveoli may show a pseudopapillary pattern (Figure 1B). If the alveolar walls are covered with tumor cells (ie, lepidic pattern), this may be mistaken for a papillary carcinoma90, 14 (Figure 1C, D). Figure 1. Images supporting the hypothesis of the collapse artifact. A, Lower panel: lung resection specimen in vacuum transport cassette (diameter 5 cm); upper panel: 2 gross slices of collapsed lung. The width of each slice is approximately one-third the width of the thoracic cavity. B, Overview of collapsed peripheral lung tissue. C and D, Adenocarcinoma in situ in collapsed lung, mimicking papillary carcinoma (hematoxylin-eosin, original magnifications x2 [B], x5 [C, center], and x20 [D, periphery]).
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