Analysis of Passive Motion of Para- and Retropharyngeal Structures During Swallowing Using Dynamic Magnetic Resonance Imaging

The purpose of this study was to analyze passive motion of the para- and retropharyngeal space (PRS) during swallowing using dynamic magnetic resonance imaging (MRI). We conducted a preliminary study involving 30 healthy volunteers who underwent dynamic MRI. Consecutive MRI axial images were obtained by examining the plane parallel to the hard palate at the level of the anterior inferior corner of C2. Anterior displacement of the posterior pharyngeal wall (PPW) was measured as a motion index of pharyngeal contraction. The displacement and internal angle of the bilateral external and internal carotid arteries (ECA and ICA) and the bilateral centroids of the PRS area, as well as the increase in PRS area, were calculated at rest and at maximum pharyngeal contraction. In most participants, the bilateral ECA, ICA, and centroids were anterointernally displaced by pharyngeal contraction. The normalized ECA displacement (r = 0.64, r ² = 0.41), normalized ICA displacement (r = 0.60, r ² = 0.37), and normalized centroid displacement (r = 0.43, r ² = 0.19) were more than moderately positively correlated with the normalized PPW displacement. The normalized PRS area increase (r = 0.35, r ² = 0.12) was weakly positively correlated with the normalized PPW displacement. These results revealed that PRS area increased as the ECA and ICA were drawn anterointernally via its passive motion by pharyngeal contraction.