Applications of electron microscopy to diagnostic pulmonary pathology

Handling and interpretation of lung transplant biopsies

The transbronchial biopsy is the gold standard for evaluation of rejection in the lung allograft. The biopsy is an invasive procedure that produces small quantities of tissue that is prone to crush artifact and is often suboptimal for evaluation. Furthermore, the biopsies should contain both alveolar tissue and airway wall to be considered adequate. Therefore, it is essential that the tissue is carefully handled at all stages of tissue processing and evaluation to ensure the best evaluation in a time sensitive and cost effective manner. Herein we describe an optimized protocol for handling and interpreting lung transplant biopsies.

Cellular events in alveolitis and the evolution of pulmonary fibrosis

"Alveolitis", as opposed to "pneumonia" sensu strictiori, is a term used to denote diffuse inflammatory changes of the pulmonary parenchyma, excluding those that result from local bacterial, fungal or other extracellular microbial growth. The various types of alveolitis are classified according to their histological characteristics and range from "luminal phagocytic" or "mural lymphoplasmacellular" and "exudative" to "fibrosing" alveolitis. In this overview, various exogenous and endogenous causes of different types of alveolitis, and the cellular events in their pathogenesis are briefly discussed to illustrate the complex mechanisms involved. Particular emphasis is placed on the possible transition from diffuse exudative to fibrosing alveolitis. It appears that pulmonary fibrosis, which is usually patchy rather than truly diffuse, does not have a uniform pathogenesis. Besides the possibility of a certain degree of a diffuse fibrosis three major pathways are evident: (1) granulation tissue budding into alveolar lumina (luminal fibrosis) (2) exudate incorporation into alveolar walls (mural fibrosis) and--at least equally important--(3) so-called collapse (atelectatic) induration (obliterative-interseptal fibrosis), a process that has largely been neglected so far.

The formaldehyde-fixed and paraffin-embedded tissues for diagnostic transmission electron microscopy: a retrospective and prospective study

The fine structures of tissues processed routinely for light microscopy were studied retrospectively in 44 tissues and tumors and prospectively in 13 tissues and tumors. In the prospective study, we fixed tissues in an ample amount of fixatives, carefully avoiding crushed and air-dried portions, and processed them by five methods. The fine structures of the retrospective cases were mostly poor or passable, whereas those of the prospective cases were generally good. All formaldehyde-fixed tissues showed varied degrees of tissue extraction, notably of lipids, membranous structures, ribosomes, glycogen, and other loose cellular and intercellular matrix materials, that was related to the status and type of tissue as well as the kind and duration of fixation, dehydration, and tissue clearance. Paraffin embedding per se appeared to cause little alteration of the fine structure. Transmission electron microscopy of the paraffin-embedded tissue appeared most useful to identify infective agents, foreign particles, and densely packed organelles or structures, usually in the differential diagnosis of neoplasms. Although many factors are difficult to control, initial careful thin slicing, judicious selection, and fixation of the tissue (even by regular phosphate-buffered formaldehyde solution) can improve the fine structure of paraffin-embedded tissues and be useful in the direct correlation of light and electron microscopic findings.

Transmission electron microscopy of percutaneous fine needle aspirates from lung: a study of 70 cases

Seventy consecutive lung fine needle aspirates (FNA) from 69 patients were examined by cytology/cell block histology, by transmission electron microscopy (TEM), and, where available, at histological follow up to determine the value of TEM in interpreting lung FNAs. Of 70 FNAs, 50 were suitable for TEM. Transmission electron microscopy was helpful in classifying seven of 10 poorly differentiated tumours, and two case histories are reported. In 26 of 30 well differentiated tumours TEM confirmed diagnosis by light microscopy. Two TEM false negatives, but no TEM false positives, were recorded. It is concluded that transmission electron microscopy of cells aspirated from lung can be helpful when unequivocal diagnosis has not been achieved.