[Significance of electron microscopy in differential diagnosis of small cell neoplasms].

The diagnosis of small cell anaplastic neoplasms is one of the difficult problems in routine pathology. In some cases, it is almost impossible by light microscopy (LM) to arrive at a correct diagnosis. Electron microscopy (EM) may contribute greatly in solving this problem. However, it is impractical to make EM examination as a routine in every difficult neoplasm. Therefore, we have reviewed, by EM specimens of 21 cases (9 cases of small cell carcinoma and 12 cases of lymphoma, previously diagnosed by LM in this hospital), and compared the light and ultrastructural features of these tumors. We found that the most important light microscopic feature to differentiate lymphoma from small cell carcinoma is the nuclear structure of tumor cells. According to the characteristics such as the shape of nuclei, the distribution of chromatin, the stereoscopic impression of nuclear section plane while focusing, the appearance of nucleoli, it is often possible to arrive at a correct diagnosis of lymphoma or small cell carcinoma by LM.