1. Department of Otorhinolaryngology, Head and Neck Surgery, Faculty of Medicine, Universitas Sumatera Utara, Medan, North Sumatera, Indonesia
2. Department of Anatomical Pathology, Faculty of Medicine, Universitas Airlangga, Surabaya, East Java, Indonesia
3. Department of Community Medicine, Faculty of Medicine, Universitas Sumatera Utara, Medan, North Sumatera, Indonesia