Clinical Outcome of Retropharyngeal Lymph Node Metastasis from Head and Neck Squamous Cell CarcinomaSusumu Nakahara,Kana Adachi,Osamu Suzuki,Yoshifumi Yamamoto,Yukinori Takenaka,Toshimichi Yasui,Atsushi Hanamoto,Takahito Fukusumi,Takahiro Michiba,Yuji Seo,Fumiaki Isohashi,Yasuo Yoshioka,Kazuhiko Ogawa,Hidenori Inohara