Observations on the growth of temporalis muscle: A 3D CT imaging study

Abstract

This study investigates the hypothesis that there is, during childhood, a disproportionate age-related expansion of the origin of temporalis muscle compared to the growth of the underlying skull. Lateral projections of 50 randomly selected 3D reformatted computerized tomographic (CT) scans (yielding 100 temporalis muscles) of children aged >0.6 to 15 years scanned for conditions that did not affect the shape of their head or face were windowed to provide the optimum delineation of temporalis muscle against the underlying bone. Vertical and anterior-posterior measurements of the muscle made independently by two observers were compared with those of the skull along the same planes. The development of the anterior temporal crest was also assessed. The intraclass correlation coefficient for differences in the measurements made by each observer ranged from good to excellent. The muscle and skull measurements were used to produce a ratio of muscle-to-skull lengths in both vertical and horizontal planes. Analysis of these ratios showed a statistically significant increase in the vertical reach of temporalis with age (Pearson correlation coefficient (R) =0.7826; p < 0.05) compared to the growth of the skull along the planes chosen for the study-but less so for its horizontal reach (R = 0.5073. p < .001). There were no significant differences between right/left or male/female measurements. There was also a substantial level of agreement between both observers in their assessment of the development of the temporal crest. The mean age of children in whom a fully formed temporal crest could be identified (10.6 years) was significantly greater (p < 0.001) than that of the 38 remaining subjects (6.0 years). These results confirm that there is, in response to increased masticatory/dietary demands during childhood, a disproportionate increase in the vertical and (to a lesser extent) horizontal reach of temporalis muscle over its origin from the temporal, frontal, sphenoid, and parietal bones compared the growth of the skull. It is proposed that surgical interference with this normal process is responsible for the soft tissue component of late-developing deformity that can occur following early (at 6-18 months of age) operations for the correction of trigonocephalic head shape associated with metopic synostosis.

Late Deformity Following Fronto-Orbital Reconstructive Surgery for Metopic Synostosis: The Role of Temporalis Muscle

“…where line a intersected line c (0.46 cm; 0.28–0.65) was not significantly different between right and left sides or when compared to measurements at the same levels taken from 50 unaffected subjects 10 (mean 0.46; range 0.28–0.65; and mean: 0.46; range 0.28–0.79, respectively).…”

“…When right and left sides were combined (n = 24), the mean vertical reach (distance b) of temporalis in unoperated MS patients (32.7 mm; standard error of mean [SEM] ± 1.7 mm) was significantly less (P = 0.0017) than that for 8 age-matched children (16 sides) from the study of normal subjects 10 (mean distance: 40.4 mm, SEM ± 1.32 mm).…”

“…When right and left sides were combined (n = 50), there was a highly significant reduction ( P << 0.001) in the vertical reach of temporalis (mean 39.4 mm, SEM ± 1.3 mm) compared to that of 42 age-matched children (right plus left sides n = 84; mean 55.27 mm, SEM ± 0.9 mm) from the study of normal subjects. 10…”

“…For this analysis, ratios b/a (muscle-to-skull proportionate vertical growth) and c/d (muscle-to-skull proportionate horizontal growth) from right and left sides of all 25 post-FOR CTs were averaged to allow comparison at scanning age with results from the previous study of normal subjects. 10…”

“…(A) Distances a, b, c, and d as measured in this and a previous study. 10 (B) A normally developed temporal crest (arrowed).…”