Biphenotypic Sinonasal Sarcoma a Newly Recognized Sinonasal Neoplasm: Case Report and Review of the Literature

First described in the literature in 2012, biphenotypic sinonasal sarcoma represents a newly recognized neoplastic entity of the sinonasal cavities. As such, differential diagnosis of sinonasal masses may overlook this rare neoplasm. We present a case report of biphenotypic sinonasal sarcoma of the left ethmoid skull base and review the literature to better define the typical presentation, histologic appearance, and treatment outcomes of this rare tumor.

A 54 year old man presented with a 4–5 month history of left sided nasal airway obstruction. Nasal endoscopy showed a large mass occupying the left nasal cavity and displacing the septum to the right. The surface had both a smooth mucosal surface as well as a stippled appearance more suggestive of an inverted papilloma. Computed tomography (CT) sinus demonstrated an expansile mass occupying the majority of the left nasal fossa and extending laterally into the maxillary antrum and superiorly to occupy the ethmoid sinuses and the region of the frontal recess. In addition, imaging showed extreme thinning versus loss of cortical continuity related to the left vertical cribriform plate and left anterior aspect of the lamina papyracea. The patient underwent endoscopic excision. Intraoperative frozen section was read as consistent with sinonasal papilloma, however, this was changed on final pathology to low-grade biphenotypic sinonasal sarcoma. The tumor was focally positive for S100 and smooth muscle actin (SMA) staining. Subsequently, the patient underwent a second surgery to fully clear margins including resection of the ethmoid skull base and repair of the skull base defect. All margins were negative upon final pathology.

Biphenotypic sinonasal sarcoma (BSS) is a rare, slow-growing sarcoma of the sinonasal cavities. The mean age at diagnosis is 50 years old and shows a predilection for women with a female to male ratio of 2:1. BSS most commonly involves the ethmoid cavity and typically involves multiple sinonasal subsites. Intracranial extension can occur in up to 10% of cases and intraorbital involvement is seen in 25%. Histologically, the tumor consists of a highly cellular proliferation of purely spindled cells arranged as fascicles and in a herringbone pattern. The tumor nuclei are uniform, hypochromatic, wavy, and bland. Necrosis is absent and the mitotic rate is low. The tumor is further characterized by co-expression of both S100 and SMA (hence, “biphenotypic”) and PAX3 gene rearrangements. Clinically, BSS is regarded as a low-grade sarcoma. Treatment consists of surgical resection with or without adjuvant radiation. Despite treatment, the recurrence rate is relatively high at 40–50%. Nonetheless, prognosis remains good with no reported cases of metastasis and only one reported death due to intracranial involvement.