Review Question - QID 109807

A 31-year-old man is referred to an otolaryngologist for ringing in his ears. He reports a 4-month history of intermittent tinnitus and deafness in his right ear. He has also experienced multiple episodes of nausea, vomiting, and vertigo with no clear etiology. He is otherwise healthy and takes no medications. He does not smoke and does not drink alcohol. He works in a loud automobile factory and rarely uses ear protection. His temperature is 99.0°F (37.2°C), blood pressure is 120/85 mmHg, pulse is 90/min, and respirations are 16/min. On exam, he is a healthy well-appearing male in no acute distress. He has a mildly ataxic gait. Audiologic examination reveals decreased hearing in his right ear. Results of a magnetic resonance imaging (MRI) scan are shown in Figure A. A biopsy of this mass would most likely stain for which of the following?