Improved nuclear contour indices for lymphoid morphometry.

The morphometric analysis of benign and neoplastic lymphoid proliferations relies heavily on nuclear shape factors to identify clefted, cerebriform or convoluted nuclei. Most studies employ the size-independent nuclear contour index (NCI = perimeter/square root area) or the closely related (nuclear) form factor to evaluate the degree of nuclear irregularity. These indices, however, cannot distinguish a truly irregular shape from a perfectly smooth elliptical one. A variation of the standard NCI is therefore proposed in which the NCI of the ellipse (NCIe) that best approximates the nuclear shape is determined to indicate the degree of nuclear elongation or ellipticity and the separate NCI of the nuclear irregularity (NCIni) is determined to indicate the true irregularity of the nuclear perimeter, independent of nuclear elongation. These two new shape factors were tested on a series of shapes and on mantle and follicular-center cells present in 3-micron plastic-embedded sections from three tonsils with reactive lymphoid hyperplasia. Whereas the standard NCI increased with increasing ellipticity or nuclear irregularity, the NCIe increased only with increasing ellipticity and NCIni with increasing nuclear irregularity. Mantle cell and, to a greater extent, follicular-center-cell nuclei showed mean NCIe and NCIni greater than what would be expected from a perfectly round nucleus. These nuclei, therefore, were both more elliptical and more irregular in outline than a perfect circle. The NCIe and NCIni were shown to vary independently in both mantle and follicular-center cells. These new and relatively simple indices should lead to a more accurate morphometric description of lymphoid cells.