Abstract

Trichodiscoma and fibrofolliculoma are follicular hamartomas exhibiting different developmental stages of the same neoplasm. Multiple fibrofolliculomas and trichodiscomas can be seen in association with Birt-Hogg-Dubé syndrome. Spindle cell predominant trichodiscoma (SCP-TD), also known as neurofollicular hamartoma, is a distinct cellular variant of trichodiscoma which morphologically lies within the same hamartomatous spectrum. In SCP-TD, the hyperplastic pilosebaceous units are embedded in a distinct cellular stroma composed of fascicular to haphazardly arranged spindle cells with wavy nuclei in a mucinous background. An unusual morphologic variant of SCP-TD with palisaded arrangements of stromal cells has been reported in two cases. Herein, we report the third case of SCP-TD with palisaded arrangements of stromal cells in a 66-year-old woman who presented with a 0.5 cm skin-colored firm papule on her left nares. Shave biopsy of the lesion showed a sclerotic dermal spindle cell proliferation with a diffuse palisaded arrangement of stroma histologically resembling a schwannoma. Compressed sebaceous lobules were seen at the periphery of the lesion. Immunohistochemistry revealed diffuse CD34 positivity in the stromal cells. The lesional cells were negative for S100, Sox10, desmin, and SMA, while factor XIIIa highlighted scattered dendritic cells. SCP-TD with palisaded arrangements of stromal cells is a rare histologic variant with no known associations with Birt-Hogg-Dubé syndrome. The stromal constituents seen in SCP-TD may resemble neoplasms with neural differentiation on limited biopsies. Identification of epithelial components and judicious use of immunohistochemistry allows for a prompt diagnosis of this rare SCP-TD variant.

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