Neuroblastoma-like schwannoma with giant rosette: A potential diagnostic pitfall for hyalinizing spindle cell tumor.

Neuroblastoma-like schwannoma (NLS) is a rare variant of a common tumor. The aim of this study is to discuss, through a literature review, the differential diagnoses of NLS while emphasizing the importance of ancillary studies. So far, 24 cases have been reported. We describe an additional case in a 64-year-old woman who had a 3-cm subcutaneous tumor on her flank. The histological examination showed an encapsulated neoplasm. Most of the tumor was made of giant rosettes. These rosettes had several sizes reaching 2.6 mm. They showed a palisade of rounded cells. Nuclei were hyperchromatic but bland. The center was made of eosinophilic cores of collagenous radiating fibrils. Neoplastic cells stained strongly for S-100 protein. In the capsule, perineural cells stained for epithelial membrane antigen (EMA). No expression of Mucin 4 (MUC4) was present. This was consistent with NLS. The same peculiar appearance of giant rosettes has been described in hyalinizing spindle cell tumor with giant rosettes (HSCT). We propose the term "neuroblastoma-like schwannoma" when there are small rosettes, "HSCT-like schwannoma" for tumors with giant rosettes and "collagen-rich schwannoma" when there are "ill-defined" structures reminiscent of rosettes. Immunohistochemical panel containing S100, EMA, and MUC4, as well as molecular testing when needed should be performed.