Trichoblastoma arising in nevus sebaceous of Jadassohn: a case report and review of the literature

Nevus sebaceous of Jadassohn (NSJ) is a congenital hamartoma that may develop secondary neoplasms, most of which are benign. Trichoblastoma (TB) is the most common benign tumor arising in NSJ but is frequently misdiagnosed as basal cell carcinoma (BCC). We report a 34-year-old female with a slow-growing nodule on a pre-existing yellowish, hairless plaque on the right chin, present since childhood. Excision and histopathology showed epidermal hyperkeratosis, acanthosis, and abnormally positioned sebaceous glands opening directly onto the epidermis, consistent with NSJ. Within the dermis, a well-circumscribed tumor composed of basaloid cells with peripheral palisading and papillary mesenchymal bodies was identified, confirming TB. This case highlights the importance of distinguishing TB from BCC to avoid unnecessary aggressive treatment. Pathologists and clinicians should be aware of this entity.