Case of the Month: December 2021
posted: December 1, 2021
This is a 57-year-old female with persistent nasal congestion and fullness that was refractory to nasal sprays. Per provided imaging, a frontoethmoidal lesion was identified in the sinonasal area with possible skull base erosion. An endoscopy was performed and a biopsy from the lesion was submitted for histopathological evaluation.
A panel of immunostains is performed and shows that the tumor cells are focally positive for S100. Desmin, myogenin and MyoD1 (all focally positive in the small area of skeletal muscle differentiation; seen on H&E slide provided) and negative for cytokeratin, SOX10 and STAT6.Beta-catenin immunostain showed rare weak staining.
Final Diagnosis: Biphenotypic Sinonasal Sarcoma (BSNS)
Biphenotypic sinonasal sarcoma (BSNS) is a rare, slow-growing soft tissue sarcoma of the sinonasal tract which features both neural (S100) and myogenic (desmin/myogenin) differentiation. It typically presents with nasal obstructive symptoms and affects females more than males (3:1). The upper nasal cavity or the ethmoid sinus are the most commonly involved sites. The tumor comprised of an infiltrative and highly cellular spindle cell proliferation. The cells are low-grade and arranged in medium to long fascicles with occasional herringbone pattern of growth with staghorn hemangiopericytoma-like vessels, bringing solitary fibrous tumor and glomangiopericytoma to the differential diagnosis.
By immunohistochemistry, the tumor cells can be positive for S100,SMA, calponin, desmin, myogenin, nuclear beta catenin and negative for cytokeratin, CD34, STAT6 and SOX10. PAX3 gene rearrangement usually occurs in BSNS with PAX3-MAML being the most common gene fusion. Biphenotypic sinonasal sarcomas are treated by local excision, with or without adjuvant radiation treatment.