1. Clinic of Neurosurgery, University Hospital “St. George”, Plovdiv, Bulgaria
2. Department of Neurosurgery, Medical University of Plovdiv, Plovdiv, Bulgaria
3. Department of Otorhinolaryngology, Medical Faculty, Medical University of Plovdiv, Plovdiv, Bulgaria
4. Department of Anatomy, Histology and Embryology, Medical Faculty, Medical University of Plovdiv, Plovdiv, Bulgaria