Transmission electron microscopy of transbronchial lung cryobiopsy samples in a cohort of fibrotic interstitial lung disease patients – feasibility and implications of endothelial alterations

Abstract We evaluated the utility of transmission electron microscopy (TEM) in transbronchial lung cryobiopsy (TBLC) samples from 16 consecutive patients undergoing routine evaluation of fibrotic interstitial lung disease (ILD). Next to routine pathology examination, 1 to 2 TBLC samples were prepared for TEM analysis and evaluated using a Zeiss LEO EM 910. Subpleural cryobiopsies and unfrozen excision biopsies from fresh lobectomy tissue of non-ILD lung cancer patients served as controls. TEM provided high-quality images with only minor cryoartifacts as compared to controls. Furthermore, in several ILD patients we found marked microvascular endothelial abnormalities like luminal pseudopodia-like protrusions and inner surface defects. These were extensively present in four (25%), moderately present in seven (43.8%), and largely absent in five (31.3%) patients. A higher degree of TEM endothelial abnormalities was associated with younger age, non-specific interstitial pneumonia pattern, higher broncho-alveolar lavage lymphocyte count, positive autoantibodies, and lower spirometry, diffusion capacity and oxygenation biomarkers. We conclude that TEM evaluation of TBLC samples from ILD patients is feasible, while the observed microvascular alterations warrant further evaluation.