Surgical anatomy of the floor of the oral cavity and the cervical spaces as a rationale for trans-oral, minimal-invasive endoscopic surgical procedures: results of anatomical studies.

Over the past 10 years, several minimally invasive procedures for thyroid surgery have been developed. Because of extensive dissection in the thoracic and neck region, the name "minimal-invasive" is misleading. The aim of this study was to define a new trans-oral access to the cervical spaces especially to the thyroid on the basis of natural orifice surgery. Three embalmed human specimens were dissected for complete review of the anatomical situation in the cervical region. In additional five fresh frozen human specimens after an experimental trans-oral endoscopic minimally invasive thyroidectomy the anatomical structures of the floor of the oral cavity as well as the anterior neck region were evaluated. It was possible to create a working space under the platysma muscle with respect to the surgical planes of the neck and fascial layers. Within this area, the pretracheal region can be reached and the thyroid gland can be visualized and resected. To access the working space, a trocar for endoscopic view is placed medially in the floor of the oral cavity sublingually. The trocar passes the muscles of the floor of the oral cavity easily without relation to relevant anatomical structures. A first exclusively sublingual approach had to be abandoned because triangulation of the instruments could not be reached. Therefore, the approach was modified by positioning the working trocars in the oral vestibule bilaterally. By this way, a road map for accessing all anterior cervical regions directly under the platysma muscle could be established and anatomical landmarks and areas of possible collateral damage could have been defined. This combined sublingual and bi-vestibular trans-oral endoscopic approach enables an easy access to all structures and spaces of the anterior neck region with respect to anatomical preformed layers neck, even to the thyroid as one of the more distant structures.