The Effects of Glossectomy and Palatal Dimension on Activity of the Tongue Muscles: A Quantitative MRI Analysis

Abstract

Purpose: The purpose of this study was to compare the tongue muscle activity of glossectomy patients and normal controls and to determine which of the following factors - palate height, palate width, and tumor size (T1 vs. T2) - might influence muscle activity after glossectomy. Methods: Muscle shortening within the hemi-tongue of 12 controls and 9 glossectomy patients was measured during the elevation and retraction of the tongue from /s/ into the /uk/ of the word "a souk" using cine-MRI and tagged-MRI. The muscle length measurements were performed on the following five tongue muscle segments: 1) genioglossus posterior (GGp), 2) geniohyoid (GH), 3) transverse anterior (Ta), 4) transverse middle (Tm), and 5) transverse posterior (Tp). Results: The controls demonstrated significant asymmetric Ta and Tp muscle shortening with the larger side shortening more than the smaller side. The patients showed relatively symmetric muscle shortening on the native and the resected sides. High palate subjects showed greater GH shortening, while wide palate subjects showed greater GH and Ta shortening. No significant interaction was found between the effects of palate dimension and glossectomy on muscle shortening. A significant positive correlation between shortening was found in five pairs of muscles in controls' both sides and in one pair (Ta and Tm) in patients' native side. The T2 patients showed less shortening than T1 patients on both the native and the resected sides for Ta and Tm. Conclusion: There were no statistically significant differences in muscle shortening between the controls and the patients, suggesting that patients were unable to adapt to an easier, asymmetric muscle activity as in controls during multiple repetitions of speech task. The effects of palate height and width were independent of the surgical effects. In controls, the muscles functioned synergistically in order to elevate the tongue by decreasing its length and width. In patients, the Ta and Tm worked in concert to decrease tongue width and create a compensatory behavior during tongue elevation. The lesser muscle shortening in T2 than T1 patients suggested greater impairment and limited muscle activity in T2 patients.