Low-Grade Biphenotypic Sinonasal Sarcoma: Case Report, Current Understanding, and Differential Diagnosis

Abstract Low-grade biphenotypic sinonasal sarcoma (BSS) is a rare, locally aggressive mesenchymal neoplasm of the sinonasal tract defined by dual expression of neural and myogenic antigens and recurrent PAX3 (paired box gene 3) gene rearrangements. We herein present the case of a 53-year-old woman with an incidentally identified lesion on surveillance magnetic resonance imaging for a pituitary microadenoma, ultimately leading to biopsy and resection of a low-grade BSS. Because of its relatively indolent behavior and extensive differential diagnosis, recognition and appropriate diagnostic workup of this entity are of utmost importance. The current understanding of low-grade BSS, its diagnosis, and differential diagnosis in the sinonasal tract are discussed.