Light microscopical morphometric classification of oncocytic and chromophobe pituitary adenomas

Light microscopical morphometry was performed on 10 adenomas with oncocytic parts (26%-50% oncocytes, group I), on 9 oncocytic adenomas with 51%-75% oncocytes (group II), and on 12 oncocytic adenomas with 76%-100% oncocytes (group III). We measured the area and circumference of nuclei and areas of cells. Furthermore, shape factors for area and circumference of nuclei and the quotients of nuclei area/cell area were calculated. Data of about 40,000 single measurements were evaluated statistically. There is a clear positive correlation of cell areas compared to the proportion of oncocytes in the respective adenoma. A gradual, steady enlargement of cells can be observed, whereas enlargement of nuclei is seen to a much less extent. Consequently the quotients of area of nuclei/area of cells become smaller with increasing oncocytic transformation, evidence that enlargement of cells takes place in favour of cytoplasm. The three adenoma groups differ significantly from each other in their average cell sizes. Regarding nuclear sizes, the difference is mainly to be seen between group II and III. Comparison of adenomas containing oncocytes with large cell and small cell chromophobe adenomas also show significant differences in sizes of cells and nuclei. Large cell chromophobe adenomas show distinctly larger nuclei, which is looked upon as a display of their endocrine activity. On the other hand, oncocytic adenomas bear comparatively small nuclei in an extended cytoplasm which may well be related to their endocrine inactivity.