Case of Symptomatic Dermal Neurofibroma With Microcystic Features

A neurofibroma is a benign neural tumor arising within a peripheral nerve sheath composed of Schwann cells, fibroblasts, and immune cells involved in the nerve. Microcystic elements have been rarely described in these tumors. Neurofibromas are classically described as unencapsulated tumors of interspersed spindle cells and mast cells in a hypocellular, myxoid stroma. These tumors are most commonly dermal and seen in almost all patients with neurofibromatosis type 1; however, they may also occur sporadically, as seen in our case here. We report a 23-year-old patient with no significant medical history who presented with a dome-shaped papule on her cheek. This slow-growing mass had been present for multiple years and was soft, inflamed, and painful. Shave biopsy was collected and sent for evaluation. The shave biopsy diagnosed a benign neural tumor with features of a rare microcystic neurofibroma. This unencapsulated tumor consisted of microcystic spaces lined by oval-shaped to spindle-shaped cells in a matrix of myxoid to collagenous-like areas. Scattered lymphocytes and mast cells were noted, with few true vessels enclosing red blood cells. The stromal cells and cells lining the microcystic spaces stained S100 and SOX-10 positive. These cells had limited CD34 staining; however, most microcystic spaces were negative. Only the few true vessels stained CD31 positive. It is important to distinguish the prominent microcystic features in neurofibromas versus schwannomas by the lack of encapsulation or Antoni A features with Verocay bodies, which are typical of the latter. Further differentiating neurofibromas versus malignant peripheral nerve sheath tumors is required, where the latter should exhibit much greater nuclear atypic, higher cellularity, necrosis, hemorrhage, and increased mitotic activity. Excision of this benign microcystic neurofibroma was not deemed necessary because of lack of clinical concern and recurrent lesions.