A Balancing Act

Question:  A patient is referred to your clinic for peripheral vertigo with caloric testing revealing left vestibular hypofunction.  Audiogram reveals normal hearing bilaterally.  The patient was treated previously for Meniere's and BPPV without benefit.  CT is obtained and shows a mass eroding the retrolabyrinthine temporal bone, extending down to the jugular foramen.  Physical exam shows no abnormality.  Of note, the patient's mother was treated for a pancreatic tumor but no head and neck or brain tumors.  What is your leading diagnosis? [Answer will be posted with next week's new question]

Answer to last week's question, Understanding All the Angles (August 10, 2015): 

The angular branch of the thoracodorsal artery.