Abstract

A 61-year-old female presented with a painless, slowly growing nodule on her upper extremity for ten years. Examination revealed a 0.5-centimeter firm, raised, subcutaneous nodule. The clinical differential diagnosis included cyst and lipoma. Histologic evaluation revealed a dermal-based dilated follicular structure containing keratinaceous debris, with radiating mature sebaceous lobules embedded in neurofibromatous stroma with peripheral stromal clefting, consistent with a neuro-follicular sebaceous cystic hamartoma (NFSCH). An S-100 stain was performed, which confirmed the neurofibromatous stroma. Folliculosebaceous cystic hamartomas (FSCHs) are non-neoplastic, biphasic hamartomas, composed of epithelial and mesenchymal components that arise from the hair follicle. They typically present as painless, slow growing, firm papules or nodules often on the face. Neural or smooth muscle elements in FSCHs are exceptionally uncommon components and, to our knowledge, only one case with neurofibromatous stroma has been reported, which was subsequently named NFSCH. The differential diagnosis of NFSCH may include neurofibromas; however, these lack the peripheral stroma clefting and dilated central follicular structure. Trichofolliculoma may be considered, especially the sebaceous variant, however, this lacks the distinctive stromal clefting. A dermoid cyst with surrounding scar may be considered. Again, the stromal clefting is a key differentiating factor, and an S-100 stain could easily tell the two entities apart if necessary. We report the second case of neurofollicular sebaceous cystic hamartoma.