Reexcision perineural invasion. Not a sign of malignancy.

Perineural invasion has been reported to occur in both benign and malignant neoplasms. We describe two cases in which perineural invasion by epithelial cells was present in reexcision skin specimens removed because of melanocytic lesions in the original biopsy material. Because of the absence of a primary epithelial neoplasm, this phenomenon was interpreted as a reactive or reparative process, most probably resulting from regenerating traumatized sweat gland ducts. On the basis of this study alone, it may not be possible to distinguish between reexcision perineural invasion and perineural invasion from a primary epithelial neoplasm. For such cases, the following histologic features serve as provisional guidelines favoring an interpretation of reexcision perineural invasion: absence of perineural spread beyond the immediate previous biopsy site, benign appearance of the perineural epithelial cells different from the appearance of the original tumor, and absence of residual epithelial tumor in the vicinity of the involved perineurium.