Symplastic trichodiscoma: a spindle-cell predominant variant of trichodiscoma with pseudosarcomatous/ancient features

Trichodiscomas are hamartomatous lesions of the follicular unit and of its surrounding stroma composed of epithelial and mesenchymal tissue elements. The dominating tissue element in trichodiscoma is the central fibrous stroma, encircled by prominent clusters of sebaceous lobules that resemble mitts. Rare variants of trichodiscomas with CD34-positive spindle cell-pedominant stroma have been described. We report a case of spindle cell-predominant trichodiscoma with prominent pseudosarcomatous/ancient features consisting in numerous large atypical spindle cells with frequent multinucleation, with no mitotic activity. The cytological changes were similar to those described in ancient schwannoma and symplastic hemangioma. We propose to call this lesion symplastic trichodiscoma. Only 1 previous case of fibrofolliculoma with pseudosarcomatous/ancient changes has already been reported. Although such lesions can appear worrisome at first glance, their benign evolution, the absence of mitosis, and the phenotypic studies excluding malignant differential diagnoses like atypical fibroxanthoma are reassuring. The precise pathogenesis of the symplastic features in schwannoma as in trichodiscoma/fibrofolliculoma is not known yet.