Possible Clues:

• Vertigo specialist, briefly
• Treebeard for one
• Otitis-treating MD
• Fictional tree person
• M.D. who may examine the sinuses
• Three-in-one M.D
• M.D. concerned with tonsils
• Fictional creature whose name is Old English for 'giant'
• Suffix with "absorb"
• Otolaryngology doc