Microcystic/Reticular Schwannoma of the Skin: A Report of a Rare Case and Brief Literature Review.

Schwannomas, categorized under benign peripheral nerve sheath tumors, exhibit a range of rare histological variants, including ancient, plexiform, pseudoglandular, epithelioid, and microcystic/reticular (MR). These variants pose a significant diagnostic challenge. In this report, we describe a case of a 34-year-old female who presented with a two-year history of a mass on her upper back. Histopathological examination revealed a well-defined and encapsulated subcutaneous nodule displaying a biphasic architecture. The predominant component consisted of hypocellular spindle cells forming reticular and cystic spaces adjacent to compressed hypercellular areas. Immunohistochemistry displayed diffuse and strong positivity for S-100 and SOX-10 while lacking expression of specific melanocytic markers, anaplastic lymphoma kinase (ALK), and cytokeratins (CKs). Intracapsular spindle cells were positive for epithelial membrane antigen (EMA). Based on these distinctive features, we arrived at the diagnosis of an MR schwannoma, an entity rarely reported in the skin. We will discuss the differential diagnosis of cutaneous neoplasms exhibiting reticular and microcystic patterns.