Abstract

Spindle cell predominant trichodiscoma (formerly known as neurofollicular hamartoma) is a rare benign hamartomatous lesion of the follicular unit characterized by a central CD34-positive cellular stroma surrounded by prominent clusters of sebaceous lobules. Typically solitary and located on the face of adults, multiple lesions may be associated with Birt-Hogg-Dubé syndrome. We describe two cases of spindle cell predominant trichodiscoma arising on the nose of two males, aged 58 and 57 years, respectively. Both lesions presented as slow-growing nodules. Histopathologic examination showed similar findings in both cases, with prominent hamartomatous sebaceous units arranged peripherally around a bland CD34-positive spindle cell proliferation. S100 and pan-keratin immunohistochemical stains were negative. Interestingly, one case showed a deep component reminiscent of spindle cell lipoma, with loss of retinoblastoma (Rb) protein expression in a subset of spindle cells. The presence of a spindle cell-lipoma component in spindle cell predominant trichodiscoma has been described, however, these two entities can be distinguished by the universal loss of Rb expression in the former corresponding to RB1 gene deletion. One case also displayed focal cytologic atypia ("symplastic change") which has also been described in the literature but does not impart any malignant phenotype. Infiltration of the subcutaneous fat and mimic muscles was also noted, which is a reflection of the anatomic site of these lesions. Herein, we describe rare examples of spindle cell predominant trichodiscoma which can show morphologic features of spindle cell lipoma and display symplastic change. The presence of muscle infiltration is also a common finding in these entities and should not raise consideration of malignancy in these benign hamartomatous lesions.

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