Anatomy Predicts the Pathology

Question: A 42 year old male is evaluated for persistent left sided otalgia and worsening hearing.  Otoscopic examination is unremarkable.  CT is obtained that demonstrates an erosive process centered near the vestibular aqueduct.  Upon further questioning, the patient notes intermittent vertiginous spells that resolve spontaneously.  What is the most likely diagnosis?    [Answer will be posted with next week's new question]

Answer to last week's question, "Scratchy Throat" (October 9, 2017)

About 5-10%.