Electron microscopy of fine needle aspiration biopsies of mediastinal and paramediastinal lesions.

The ultrastructural cytologic study of fine needle aspiration (FNA) biopsies from eight cases with mediastinal and paramediastinal lesions is reported. In these cases, electron microscopy (EM) was essential in cytologically determining the correct type of the cancer cells. The results in these cases suggest that portions of FNA biopsies from deep sites, where aspiration is difficult or requires computed tomographic scanning, should be routinely processed for plastic embedding, so that EM examination can be performed if the cells are undifferentiated, scanty or poorly preserved by light microscopic examination. The proper cytologic identification of the cell might, in fact, have a major bearing on the therapeutic choices and on the prognosis.