Longitudinal Magnetic Resonance Imaging Evaluation of Craniofacial Muscle Changes Following Radiotherapy in Nasopharyngeal Carcinoma

Aim: Nasopharyngeal carcinoma (NPC) is a radiosensitive head and neck malignancy typically arising in the Rosenmüller fossa. Radiotherapy (RT), while effective, is associated with adverse effects such as dysphagia and muscle atrophy. While pharyngeal constrictors have been extensively studied, the impact of RT on masticatory and suprahyoid muscles remains underexplored. This study aimed to quantitatively assess MRI-based changes in the thickness of masticatory and suprahyoid muscles in NPC patients before and 18–24 months after RT and to compare these findings with healthy controls. Material and Methods: MRI data from 31 NPC patients and 50 healthy controls were retrospectively analyzed. Muscle thickness was measured bilaterally on standardized T1- and T2-weighted sequences for the masseter, medial/lateral pterygoid, temporalis, geniohyoid, mylohyoid, digastric (anterior belly), and genioglossus muscles. Statistical analyses included paired and independent t-tests, ANOVA, and Chi-square tests (Python v3.11; p < 0.05). Results: Pre-RT patients showed significantly reduced left masseter thickness compared to controls (p = 0.0022). Post-RT, the masseter and medial pterygoid muscles demonstrated up to 30.61% atrophy (p < 0.00001). Minor, non-significant increases were seen in the lateral pterygoid and digastric muscles. Right-sided tumors showed higher ipsilateral muscle thickness. Genioglossus hypertrophy was observed in bilateral cases. Males had thicker muscles than females, and muscle thickness declined with age. Conclusion: RT leads to significant atrophy in key masticatory muscles in NPC patients. Muscle asymmetry may precede treatment and reflect tumor laterality. MRI-based assessment offers valuable insights.