Electron microscopy has proved to be a valuable diagnostic tool in surgical pathology. As shown in three illustrative cases, the procedure is most useful in accurately classifying light microscopically diagnosed undifferentiated tumors of the head and neck, and is also helpful in predicting the origin of cervical lymph node metastasis in occult cancer. It also serves to quality control diagnoses made by light microscopy.
All surgical specimens are fixed in a fixative that gives adequate ultrastructural preservation and allows retrieval and examination by electron microscopy, if indicated. Recent technical improvements have resulted in a turn-around time of less than two days, thus making diagnostic electron microscopy clinically useful. The ultrastructural examination of undifferentiated tumors has a high diagnostic yield, often obviating additional diagnostic procedures and exploratory surgery. The correct diagnosis results in appropriate therapy and accurate assessment of prognosis.