A 52-year-old man presents with a 3-year history of progressive unilateral hearing loss and tinnitus. Audiometry reveals asymmetric sensorineural hearing loss with disproportionately poor word recognition score. MRI with gadolinium shows the structure marked **A** in the diagram — a well-demarcated, avidly enhancing mass in the cerebellopontine angle with extension into the internal auditory canal, producing an "ice-cream cone" appearance. Which of the following best describes the cellular origin and pathological classification of this lesion?