 Up to 16 of vHL patients are known to develop endolymphatic sac tumors in the inner ear that can cause permanent hearing loss. However, the ELSTs are often not found before hearing loss has already occurred. The challenge for doctors is to diagnose the ELSTs at early stages before they cause often irreversible deafness. In order to find ELSTs before they cause hearing loss, it is important to screen for the tumors prophylactically, that is screen all vHL patients regardless of whether or not they have symptoms. 