Estimation of the volume-weighted mean nuclear volume discriminates Spitz's nevi from nodular malignant melanomas

Spitz's nevi are benign melanocytic skin tumors that are usually differentiated from nodular malignant melanomas by histopathologic criteria. Often, however, the architectural pattern and cytologic features of Spitz's nevi and nodular melanomas are similar. Hence, Spitz's nevi may be confused with nodular malignant melanomas at the histopathologic level.

The determination of volume-weighted mean nuclear volume (Vv) uses a technique that permits an unbiased and efficient estimation of nuclear volumes in tissues. In this study, Vv was determined in 13 Spitz's nevi and 14 nodular malignant melanomas to investigate whether this stereologic approach may be of use in the differentiation of these two tumors. Vv was determined by computer-assisted image analysis (IBAS 20, Kontron, Germany) on Feulgen-stained sections using stereologic estimation of the Vv.

The Vv (+/- SD) of Spitz's nevi was 491.6 micron3 (SD +/- 175.1), whereas nodular malignant melanomas exhibit a significantly higher (p < 0.001) Vv of 775.2 micron3 (SD +/- 205.4). This difference was even more pronounced when the deeper portions of the lesions (Spitz's nevi: 443.1 micron3, SD +/- 142.4; nodular malignant melanomas: 864.1, SD +/- 169.6) were investigated. In addition, we found that in relation to the depth of the lesions the mean Vv decreased in Spitz's nevi, whereas it increased in nodular melanomas.

We found that (i) nodular malignant melanomas reveal a larger Vv than Spitz's nevi in general, and (ii) in contrast to malignant melanomas, the Vv of nevomelanocytes in Spitz's nevi decreases in the deeper portions of the dermis. Thus, Vv may be regarded as a helpful tool for the differential diagnosis of Spitz's nevi and nodular malignant melanomas.