Silhouette symmetry: an unsupportable histologic criterion for distinguishing Spitz nevi and compound nevi from malignant melanoma.

BACKGROUND: In 1989, Ackerman proposed that pattern analysis can be a more accurate method of evaluating neoplasms than assessment of nuclear morphology. He stated that malignant melanomas tend to be asymmetrical, and benign melanocytic neoplasms tend to be symmetrical.
METHODS: We examined a series of typical Spitz nevi, compound nevi, and malignant melanomas with the loupe and with higher magnifications. We also considered pattern analysis from the standpoint of solid geometry.
RESULTS: The ratio of symmetrical to asymmetrical lesions (visualized in histologic sections) in malignant melanomas approximated that of Spitz nevi and compound nevi. The configuration seen in sections does not necessarily reflect the three-dimensional configuration of a lesion. Lesions with three-dimensional reflective symmetry cannot be shown to have this property in sections unless cuts are made perpendicular to the plane of symmetry, which is an impossibility.
CONCLUSIONS: The presence or absence of symmetry in sections of neoplasms must be considered coincidental or focal. Using symmetry as a criterion to distinguish malignant melanomas from Spitz nevi and compound nevi is without validity on both theoretical and empirical grounds.