A 19-year-old male student presents with a 4-month history of progressive left-sided nasal obstruction and recurrent nosebleeds that have required hospital visits for epistaxis control. He denies systemic symptoms, weight loss, or constitutional complaints. Nasal endoscopy reveals a smooth, pulsatile, reddish mass in the left nasopharynx. MRI shows a heterogeneous mass with multiple flow voids and widening of the left pterygopalatine fossa. The mass extends into the sphenoid sinus. Before surgical planning, which of the following is the most appropriate next step in management?