Rippled-pattern sebaceoma.

A 71-year-old woman had a dome-shaped, slightly erythematous nodule on the anterior scalp. The nodule histopathologically revealed sebaceoma based on the silhouette and cytology. A notable and unique finding was often observed in the aggregations of sebaceoma; an arrangement of small, monomorphous, cigar-shaped basaloid cells in linear rows parallel to one another, resembling the palisading of nuclei of Verocay bodies, namely a rippled-pattern. Although we are not certain that sebaceoma can be clearly separated from trichoblastoma with sebaceous differentiation in all cases, in the present case, the absence of an abundant and densely fibrotic stroma, of follicular differentiation, and of a palisading border in the neoplastic aggregations as well as the presence of many vacuolated cells and tiny duct-like spaces favors the diagnosis of sebaceoma rather than trichoblastoma with sebaceous differentiation. Based on the expression patterns of CKs as well as similar cytological features between germinative cells in our case and immature cells in the mantles of normal vellus follicles, we believe that rippled-pattern sebaceoma is composed of immature sebaceous germinative cells with some foci of advanced sebaceous differentiation (toward the sebaceous duct and sebaceous lobule).