Endoscopic Endonasal Anterior Skull Base Resection for a SMARCB1-Deficient Sinonasal Carcinoma Arising From the Olfactory Cleft: A Case Report.

A switch/sucrose non-fermentable (SWI/SNF)-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1)-deficient sinonasal carcinoma is a rare, aggressive malignancy characterized by loss of nuclear expression of the SMARCB1 protein, also known as integrase interactor 1 (INI1). A 66-year-old man presented with recurrent right-sided epistaxis. Computed tomography and magnetic resonance imaging demonstrated a 50 × 15 × 36 mm mass centered in the right olfactory cleft and extending into the ethmoid sinus. The tumor abutted the anterior skull base, with suspected cribriform plate invasion but no overt intracranial extension. Biopsy showed an undifferentiated carcinoma with loss of SMARCB1/INI1 expression, and the tumor was staged as cT3N0M0. Endoscopic endonasal resection was performed, including unilateral anterior skull base and dural resection to obtain an adequate surgical margin. The skull base defect was reconstructed using a dural substitute, fascia lata, and a vascularized nasoseptal flap. Although the tumor was fully mobilized as a single specimen, it fragmented during transnasal extraction, precluding accurate histopathological assessment of the surgical margins. No dural invasion was identified. Postoperative intensity-modulated radiotherapy was delivered to a total dose of 60 Gy. The patient remained free of recurrence eight months after surgery. This case suggests that endoscopic anterior skull base resection combined with postoperative radiotherapy may provide favorable short-term disease control in resectable SMARCB1-deficient sinonasal carcinoma arising from the olfactory cleft. In high-grade malignancies centered near the cribriform plate, anterior skull base resection should be considered to obtain an adequate surgical margin, even in the absence of overt radiographic intracranial extension, although the extent of resection must be individualized.