Prediction of different airway gradings in T1-2 laryngeal cancer with anterior vocal commissure involvement

Background: A retrospective analysis was conducted to investigate the clinical ecacy of the modied Mallampati test (MMT) combined with indirect laryngoscopy in measuring glottic exposure levels of early glottic laryngeal carcinoma (T1-2) with anterior vocal commissure involvement. Methods: One hundred eighty-two patients with early glottic laryngeal cancer were divided into two groups: one group comprised patients treated with transoral carbon dioxide laser microsurgery (TLM, 65 patients), and the other group comprised patients treated with open partial laryngectomy (OPL, 117 patients). The MMT and indirect laryngoscopy were used to re-evaluate the level of glottic exposure and to classify the patients based on these levels. The local control and disease-free survival rates of those patients were measured based on their MMT and indirect laryngoscopy classications. Results: The 5-year local control rate was signicantly different between the two groups according to the MMT (log-rank test: χ2=4.020, P=0.045, 90.9% in the OPL group vs. 71.4% in the TLM group). For patients diagnosed with grade IV tumors using indirect laryngoscopy, the 5year local control rate was signicantly different between the two groups (log-rank test: χ2=4.076, P=0.044, 91.7% in the OPL group vs. 54.7% in the TLM group). Among patients diagnosed with grade III or IV tumors using indirect laryngoscopy and with class III or IV tumors using MMT, the 5-year local control rate was signicantly different between the two groups (log-rank test: χ 2 = 8.037, P = 0.005, 97.14% in the OPL group vs. 75.47% in the TLM groups). Conclusions: The combination of the MMT and indirect laryngoscopy to evaluate dicult airways is relatively simple and is very useful for surgeons to better prepare for surgery. research has been conducted to investigate the clinical application of the Mallampati test (MMT) in combination with indirect laryngoscopy for diagnosing glottic laryngeal carcinoma (T1-2) with AVC. In this retrospective study, clinical data that were collected over the past 10 years at the First Aliated Hospital of Sun Yat-sen University and that met the inclusion criteria were analyzed to investigate the clinical application of the MMT combined with indirect laryngoscopy in evaluating the clinical ecacy of different surgical methods on glottic laryngeal carcinoma (T1-2) with AVC. Our ndings can provide guidance to physicians in preoperative assessments of patients with early glottic laryngeal cancer with AVC involvement and in choosing the appropriate treatment.

Clinical data were collected from 182 patients with early glottic laryngeal carcinoma (squamous cell carcinoma con rmed pathologically) who underwent concurrent surgery at our unit between January 2006 and January 2017. Patients were divided into the TLM group (65 patients) and the open partial laryngectomy (OPL) group (117 patients). Among them, TLM was implemented in 2010, and OPL was implemented in 2006. The baseline of patients in the open surgery group from 2006 to 2010 was no different from that of patients after 2010. (Table 1). The exclusion criteria were as follows: 1) pathological con rmation of tumors other than laryngeal squamous cell carcinoma (such as adenocarcinoma or papillary carcinoma); 2) clinical stage other than T1-2N0M0 (according to2017AJCC); 3) history of oropharyngeal surgery; and 4) severe dysfunction of major organs.

Choice of surgical methods
The decision to select laser surgery or open surgery was based on the patient's tumor size, preoperative and intraoperative exposure, preoperative imaging evaluation, the patient's preference, and the surgeons' experience.

TLM Surgical equipment
A Zeiss S88 operating microscope (German Zeiss), a Sharper-30c carbon dioxide laser and coupler (Israel Medical Company), a support laryngoscope (STORZ, Germany) and a laryngeal microsurgery instrument were used. Single indicator to assess the local control and disease-free survival rates of the two groups MMT As shown in Tables 3and 4 and Figure 1, no signi cant difference was found between the two groups in terms of the local control rates and disease-free survival rates of class I, II, or III patients according to the MMT. The 5-year local control rate of class IV patients was signi cantly different between the two groups (log-rank test: χ2=4.020, P=0.045). The local control rates of class IV patients in the OPL and TLM groups according to the MMT were 90.9% and 71.4%, respectively. The difference in disease-free survival between the two groups was similar to the difference in local control.   a Follow-up time of the study subjects did not reach the corresponding time.

Indirect laryngoscopy
As shown in Tables 3and 4 and Figure 2, there was no signi cant difference in the local control and disease-free survival rates between the two groups among grade I, II, and III patients according to indirect laryngoscopy at 5 years. However, the 5-year local control rates of patients with grade IV airways (indirect laryngoscopy) were signi cantly different between the OPL and TLM groups (log-rank test: χ2=4.076, P=0.044), with 5-year local control rates of 91.7% and 54.7%, respectively. The same pattern was observed for disease-free survival rates between the two groups.
Local control rate and disease-free survival rate based on a combination of indicators Correlation between indirect laryngoscopy and the MMT Data analysis showed that there was a moderate correlation between indirect laryngoscopy and the MMT (r=0.646, P<0.05).

Discussion
It has been reported that the incidence of DA is 6.1%-10.1%. [13,14] According to the conventional MMT grading and laryngoscope mirror grading, MMT-, IV and laryngoscope mirror III and IV were regarded to have di cult airways. Our showed that prevalence was similar between grades I and II and grades III and IV. Although incidence of airway dysfunction should have had a certain deviation, the data of our evaluation results showed such deviation didn't exist among patients population in this study.
If the patient has obvious anatomical or pathological abnormalities of the airway, it is necessary to determine whether DA exists before further surgery. Predictive studies are clinically signi cant when the structures are normal, but other factors may make glottis exposure di cult. To predict whether an airway is di cult, either a single factor model or a combination of two or more factors should be used.

MMT
MMT is widely used in DA diagnosis. In 1983, Khan et al. [15] proposed a method to classify DAs into three levels according to larynx structure.
Nasir et al. [16] expanded this classi cation to four levels, which drew much interest among researchers, but its clinical practice has been questioned since its classi cation was introduced. The MMT is a comprehensive index that is mainly based on mouth opening width, tongue size and mobility, maxillary movement, other intraoral structures and cranial and cervical joint movements. The grading of glossopharyngeal structure is closely related to the ease of endotracheal intubation under direct laryngoscopy, so it has remained the primary assessment method for anesthesiologists. Adamus et al. [17] reported that the speci city and sensitivity of the MMT are not high, limiting its clinical use. In addition, some scholars believe that its accuracy is moderately low [18,19]. Other reports, including meta-analyses, have shown divergent results. Lee et al. [20] suggested that the MMT should not be used as the sole assessment tool, a view shared by most scholars. When the MMT is used alone, there is no way to fully con rm the DA. Stud have shown that the combination of the MMT with hyperthyroidism or other airway assessments can improve the diagnostic accuracy up to 50-80% [10,21]. El-Ganzouri et al. [22] analyzed 10507 cases, with MMT class III as the boundary value, and de ned Cormack-Lehane grades 3 and 4 as tracheal intubation di culties. The sensitivity of the MMT in predicting tracheal intubation di culty was 44.7%, while its speci city was 89.0%, with a positive predictive value of 21% and a negative predictive value of 96.1% [23]. From this perspective, the MMT has clinical value. Since the current study was a retrospective analysis in nature and did not obtain the number of speci c di cult exposures during surgery, the relevant sensitivity, speci city and other indicators were not evaluated. However, our research did show a statistically signi cant difference between the two groups among class IV patients according to the MMT, indicating that although a class III or IV classi cation according to the MMT is de ned as a DA, the score may not be su cient in the single factor analysis. The results of this study suggest that the MMT is a more accurate predictor of DA among class IV patients.

Indirect laryngoscopy
The indirect laryngoscope was invented in 1854 by Spanish vocal teacher Manuel Garcia, who became the rst person to observe his own throat structure. His design was subsequently improved by Professor Ludwig Turck, while the predecessor of modern laryngoscope was designed by Johann Nepomuk Gzermak in Poland in 1858. This technology has been rapidly utilized as one of the most common and simple inspection instruments in the otolaryngology eld. In 1997, Yamamoto et al. [12] rst described airway grading using indirect laryngoscopy as follows: grade I, the entire glottis is visible; grade II, the posterior commissure is visible; grade III, only the epiglottis is visible; and grade IV, no laryngeal structures are visible. Generally, grade III or above is indicative of DA. Sanchez-Morillo et al. [23] found that indirect laryngoscopy was an independent and reliable tool to diagnose DAs when combined with 70° rigid endoscopy and direct laryngoscopy. Additionally, Yamamoto et al. [12] found that the indirect laryngoscopy classi cation is more accurate than the direct laryngoscopy prediction, indicating that indirect laryngoscopy alone has certain clinical signi cance. Therefore, the use of indirect laryngoscopy alone was assessed in this study. When the indirect laryngoscopy result was grade IV, the two treatment groups showed statistically signi cant differences in both 5-year local control and disease-free survival rates. Additionally, the 5-year local control and disease-free survival rates based on indirect laryngoscopy were lower than those based on the MMT, indicating that indirect laryngoscopy grade IV could better diagnose DA and lead to higher diagnosis accuracy, which is consistent with the results from previous reports.

Combination of the MMT and indirect laryngoscopy to evaluate DAs
In clinical practice, the combination of multiple methods can diagnose DAs more accurately and reliably. For example, Merah et al. [21] combined the MMT, intercondylar distance, chest-to-twist distance, mandible length and upper and lower incisor distance to diagnose DAs. The joint diagnostic value of this combined method was the highest, but multiple shortcomings limited the application of this method. One of the shortcomings is that this combined approach is not easy to implement in practice. Therefore, our study was designed to elucidate DA patients with different exposure levels based on two assessment tools and to analyze the survival rate of patients with laryngeal cancer with AVC based on these tools. Our research found that patients with DAs (class III/IV) who underwent TLM had a lower local control rate than those who underwent OPL. Because this difference was statistically signi cant, combining the MMT with indirect laryngoscopy can re ect to some extent the exposure di culties that affect prognosis. This study has clinical signi cance when the anatomy looks normal, but there may be di culties in glottic exposure. After all, patients with MMT grade III or indirect laryngoscopy class III airways account for the majority of patients with laryngeal cancer with AVC. Our research showed that class III/IV and grade III/IV classi cations are more meaningful when combined. In addition, these two methods are relatively simple to implement and should be used more often in clinical practice.
Strategy for di cult glottic exposure Ohno et al. [24] reported that laryngoscopy and body posture are important for AVC exposure. Some scholars have found that assessing glottic exposure requires information on sex and thyroid mandibular angle (TMA). If the patient is female and the TMA is greater than 120°, the positive local control rate can reach as high as 94.6% [25,26]. In predicting di cult airway exposure, Piazza et al. determined the classi cation based on AVC exposure under laryngoscopy with different lens size and positions, and found that laryngoscopy with different lens size and positions had a predictive effect on classifying di cult AVC exposure [27].For patients who have early glottic laryngeal cancer with AVC involvement and undergo laser surgery, the AVC exposure eld requirements are higher. In addition to adequate preoperative assessment, surgical techniques and surgeon experience also affect surgical outcomes [28]. In laser surgery, we used STEINER tubular laryngoscope with channel (KARL STORZ, No. 8661CN) to expose the lesion. If the anterior joint part was not well exposed, STINER laryngoscope (No. 8661DN) ) with a slightly smaller tube was used. In cases of poor glottic exposure, the smaller STORZ mirror can be replaced with a more rigid endoscope (30°, 45°, or 70°) to fully expose the lesion [29]. For posterior joint or hypopharyngeal lesions, we used LINDHOLMR surgical laryngoscope (KARL STORZ) with a wider distal end and a larger. If the target area is still insu ciently exposed, the thyroid cartilage can be pressed to shift the vocal cords before initial exposure or after the rst 1/3 of the area is exposed. The goal is to remove the lesion under direct vision during surgery. If the MMT or indirect laryngoscopy is used alone, although there is a certain correlation between these classi cations and DAs, surgeons should be aware of the possibility of false negative results and the inability to diagnose DAs or the possibility of unnecessary treatment when false positive results occur. It is important to balance the pros and cons and make optimal decisions for patients. For laryngeal cancer with AVC involvement, whether it is DA or another impeding factor, it is necessary to comprehensively evaluate all aspects. However, there is no indicator or method that can be used to identify appropriate exposure. Therefore, if there is still poor exposure after trying different approaches during surgery, the surgeon must be willing to adjust the treatment strategies in a timely manner.

Research limitations
Since this was a retrospective study, not a prospective study,more study is needed to clarify the correlation between preoperative judgment and postoperative prediction. There were some missing data regarding related factors, which may lead to false positive results. Second, further follow-up and long-term comparison of the local control and disease-free survival rates of TLM and OPL groups are needed. Additional postoperative patient survival data, including MMT scores, upper and lower incisor spacing, hyperthyroidism spacing, mandibular advancement amplitude, head and neck movement amplitude, laryngoscopic exposure grade and BMI, need to be further analyzed.

Conclusions
For T1-2 laryngeal cancer with AVC involvement,The combination of the MMT and indirect laryngoscopy to evaluate DAs is relatively simple and can be used in clinical practice.

Declarations
Ethics approval and consent to participate