Histopathologic analysis has been conducted on 36 cases of interstitial fibrosis of the
lung. The key findings of histologic criteria of interstitial fibrosis are alveolar narrowing
and desquamation of epithelial cells in the alveoli, and alveolar septal inflammation,
septal fibrosis and honeycombing in the interstitium. In the early stage, the loose
fibrillar collagen fibers accumulated irregularly surrounding bronchioles and small vessels
with extension to alveolar interstitium. As the lesion advanced, fibrillar fibers gathered
in the interstitium with nodular form. Alveolar narrowing, partly hyaline change of
vessels or thick bundles of interstitial fibers were noted. In the late stage, diagnostic
findings were irregular collagen bundles with smooth muscle hypertrophy in the
interstitium, hypertrophy of the arteriolar wall and especially cystic or honeycomb
appearance of alveoli. The problem of transbronchial fiberoptic lung biopsy is so small in
size of speicmen that it cannot represent the lesion of inhomogeneous interstitial lung
disease. In advanced disease and observation of alveolar epithelial changes, the
transbronchial fiberoptic lung biopsy is useful. However, the open lung biopsy is more
useful to make a diagnosis of early disease with activity.
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