A 28-year-old man from rural India presents with a 3-year history of foul-smelling otorrhoea from the left ear, conductive hearing loss, and recurrent ear infections. Otoscopy reveals a retraction pocket in the posterosuperior quadrant with granulation tissue. High-resolution CT temporal bone shows an expansile lesion in the epitympanic recess with bone erosion of the ossicles and lateral semicircular canal. What is the most appropriate next step in management?