Study of the head and neck position in microlaryngoscopy using magnetic resonance imaging.

Several studies have critically analyzed the ideal position for laryngeal exposure during microlaryngoscopy; however, these studies have lacked the ability to evaluate the head and neck position while maintaining a direct view into the airway. Therefore, a newly established two-curve methodology was used to investigate the influence of head and neck position during microlaryngoscopy in MRI images. Fourteen normal adult volunteers were used in this magnetic resonance imaging study. The airway was divided into two curves in the sagittal plane at the center of the airway in three head and neck positions: extension-extension, neutral and flexion-extension position. The airway passage curves, point of inflection and its tangent, the line of laryngoscope, line of hyoid bone and mandible were plotted on each scan. Angles and area formed by these lines were calculated to evaluate the airway morphology changes. The flexion-extension position caused a reduction in the area between the line of laryngoscope and curves, but there was no significant difference between the three positions (p = 0.664). The flexion-extension position also resulted in the lowest angle values for α (angle between the tangent and horizon, p = 0.000), β (between the line of hyoid and horizon, p = 0.002) and δ (between the line of mandible and horizon, p = 0.004). Our study provides a better understanding of the changes in normal airway morphology during microlaryngoscopy in different positions, reinforcing the concept that flexion-extension position is the optimal position for microlaryngoscopy.