1. American Tinnitus Association. Information about tinnitus. Portland (OR): Tinnitus Today; 1979.
2. Medical evaluation;Shulman,1991
3. Dorland's pocket medical dictionary. 22nd edition. W.B. Saunders Co: Philadelphia: London Toronto. p. 510.
4. Oxford textbook of palliative medicine. 3rd edition. Doyle D, Hanks G, Cherny, Calman K, editors.
5. Bulletin of the American College of Surgeons, vol. 90, No.8, 2005.