Nucleolar ultrastructure in low- and high-grade non-Hodgkin's lymphomas

Transmission electron microscopy was used to study the ultrastructure of nucleoli in seven high‐ and seven low‐grade non‐Hodgkin's lymphomas. Nucleoli with a single large fibrillar centre were predominantly seen in the low‐grade group, while the majority of nucleoli in high‐grade lesions contained several small fibrillar centres of approximately equal size. A third type of nucleolar appearance was identified, with a large central fibrillar centre surrounded by numerous small ‘satellite’ fibrillar centres. This nucleolar configuration was the least common but was more often seen in low‐grade than in high‐grade lymphomas. The mean fibrillar centre cross‐sectional area was determined for each group and measured 278 800 nm2 for low‐grade non‐Hodgkin's lymphomas and 62 507 nm2 for high‐grade lymphomas (P < 0·001). These results show that fibrillar centre size and morphology correlates with grade of non‐Hodgkin's lymphoma and may reflect differences in ribosomal deoxyribonucleic acid transcription.