Introduction: Transoral endoscopic surgeries provide excellent oncologic outcomes while preserving speech and swallowing ability. During transoral surgery, a straight plate tongue depressor such as the FKWO retractor is used to achieve laryngopharyngeal exposure and allow the use of straight instruments. It is more difficult to expose the surgical field with straight tools such as the FKWO retractor and rigid laryngoscope than with curved tools. In some patients, the entire hypopharynx is not visualized with straight tools. Inadequate hypopharyngeal exposure may lead to incomplete tumor resection. Predictors of difficult hypopharyngeal exposure during transoral surgery have not been reported. The aim of this study was to evaluate the parameters in the preoperative assessment that affect hypopharyngeal exposure.
Methods: Between April 2015 and March 2017, 51 patients underwent transoral surgery. Before surgery, parameters regarding the patient’s neck and face such as modified Mallampati index, thyroid mental disease (TMD), and ability to fully open the mouth were evaluated. General parameters such as age, weight, height, and body mass index (BMI) were also evaluated. Cephalometry and cervical spine radiography were performed preoperatively to evaluate the size of the submandibular bone, mouth opening, and cervical spine extension. Mandibular bone parameters such as intergonion distance, mental-gonion distance, articulare-gonion distance, and aperture angle were measured. At the time of transoral surgery, the FKWO retractor was inserted to expose the hypopharynx and a flexible endoscope with angulation in 4 directions was used to visualize the hypopharynx. Patients were divided into two groups according to hypopharyngeal exposure. Patients with exposure of the hypopharynx that was insufficient to perform transoral surgery were classified into the difficult hypopharyngeal exposure group (DHE). Others were classified into the non-difficult hypopharyngeal exposure group (non-DHE). Parameters were enrolled to evaluate the relationship between these parameters and DHE status.
Results: This study included 51 patients, 37 in the non-DHE group and 14 in the DHE group. There were no significant differences between the non-DHE and DHE groups in age, height, weight, and BMI. On radiographic evaluation, there was a significant difference in the degree of cervical kyphosis between non-DHE and DHE patients (56.4 ± 1.9° vs. 38.7 ± 3.5°). Receiver operating characteristic curve analysis showed that with a cervical kyphosis degree cut-off value of 46.6°, predicted sensitivity and specificity for detecting the risk of DHE were 78.57% and 80.56%, respectively. On the other hand, there were no significant differences in ability to fully open the mouth or Mallampati index between non-DHE and DHE patients. On cephalometric evaluation, there were no significant differences between non-DHE and DHE patients in intergonion distance, mental-gonion distance, articulare-gonion distance, and thyroid mental distance. A significantly higher proportion of DHE patients had a history of radiotherapy compared with non-DHE patients.
Conclusion: Patients with limited cervical extension and a history of previous radiotherapy might have difficult hypopharyngeal exposure during transoral surgery. This is the first report to suggest a classification system for hypopharyngeal exposure during transoral surgery. A baseline for estimating DHE will be useful in surgical decision-making for otolaryngologists.