Neurosecretory granule-like structures in lymphomas.

This report concerns the finding of round to ovoid electron dense, membrane bound structures 100 to 300 nm. in average diameter in four non-Hodgkin lymphoma cases studied ultrastructurally. In three of the cases the material for electron microscopy was obtained from lymph nodes. Two of the lymph nodes were replaced by nodular, poorly to moderately differentiated lymphocytic lymphoma, and the third was effaced by a diffuse histiocytic lymphoma. In the fourth case the specimen examined consisted of a spleen also replaced by nodular, poorly differentiate lymphocytic lymphoma. All cases appear to be primary abdominal lymphomas. The structures identified in the four lymphomas were similar in appearance to membrane bound neurosecretory granules when viewed by electron microscopy. It is proposed that the electron dense particles may represent peculiar lysosomes. Further cytochemical examination is needed to adequately characterize them. Although the presence of typical lysosomal granules in normal lymphocytes is a well known finding, we have not seen the type of granules described here i normal lymphocytes. Owing to the frequent use of electron microscopy examination to differentiate small cell undifferentiated (oat cell) carcinomas and, occasionally, other neuroendocrine neoplasms from lymphomas, the finding of these neurosecretory-like structures in lymphomas creates significant difficulty in the differential diagnosis and separation of these neoplasms by ultrastructural analysis.