Abstract:

Rosettes in surgical pathology usually represent neural neoplasm; however, rosettes and rosette-like structures are also reported in non-neural lesions, including melanocytic neoplasms. Structural variations of these rosettes include Homer-Wright, Flexner-Wintersteiner, and true ependymal. Pseudorosette types include vascular and Meissnerian. All these forms have been described in various melanocytic lesions. We describe a case of desmoplastic Spitz nevus with Homer-Wright rosette in histological congruity with an earlier reported case and discuss the bias and significance of rosette formation in melanocytic neoplasms in general. A 19-yer-old female presented with a flesh-colored nodule on the left upper back measuring about 1 x 1 cm. The clinical impression included dermatofibroma and melanocytic nevus. Histologic examination of a shave biopsy revealed dermal proliferation of epithelioid and spindled cells with prominent eosinophilic cytoplasm containing an enlarged vesicular nucleus with a prominent nucleolus. Mitoses were not identified. Some of the nests in the papillary dermis exhibited a rosette-like arrangement with a solid center corresponding to the Homer-Wright type. The mart-1 stain was positive, and the ki67 stain showed low proliferative activity. The p16 stain demonstrated no loss of expression. We describe the second case of a desmoplastic nevus with Homer-Wright rosette formation. In melanocytic lesions, rosettes are most frequently reported in melanomas, followed by Spitz nevi and unusual nevi. Their occurrence in common acquired or Clark’s nevi is exceptionally rare. Since rosettes are encountered in lesions towards the aggressive spectrum of clinical behavior, their presence should prompt a more thorough evaluation supplemented by immunohistochemistry and examination of multiple levels from the block.

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Sary Alothman

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(Poster #370) Rosette Formation in Desmoplastic Spitz Nevus