Anatomical changes in the pharyngeal constrictors after chemo-irradiation of head and neck cancer and their dose–effect relationships: MRI-based study

PurposeDysfunction of pharyngeal constrictors (PCs) after chemo-irradiation of head and neck (HN) cancer has been proposed as major cause of dysphagia. We conducted prospective MRI study to evaluate anatomical changes in the PCs after chemo-irradiation, to gain insight of the mechanism of their dysfunction and their dose–effect relationships. The PCs were compared to the sternocleidomastoid muscles (SCMs), which receive high doses but do not relate to swallowing.Patients and methodsTwelve patients with stage III–IV HN cancer underwent MRI before and 3 months after completing chemo-irradiation. T1- and T2-weighted signals and muscle thickness were evaluated for PCs (superior, middle, and inferior), and SCMs. Mean muscle doses were determined after registration with the planning CT.ResultsT1-weighted signals decreased in both PCs and SCMs receiving >50 Gy (p < 0.03), but not in muscles receiving lower doses. T2-weighted signals in the PCs increased significantly as the dose increased (R2 = 0.34, p = 0.01). The T2 signal changes in the PCs were significantly higher than the T2 changes in the SCMs (p < 0.001). Increased thickness was noted in all PCs, with muscles receiving >50 Gy gaining significantly more thickness than PCs receiving lesser doses (p = 0.02). In contrast, the SCM thickness decreased post-therapy (p = 0.002).ConclusionsThese MRI-based findings, notably the differences between PCs and SCMs, suggest that underlying causes of PC dysfunction are inflammation and edema, likely consequential to acute mucositis affecting the submucosa-lying PCs. These results support reducing mean PC doses to ⩽50 Gy, as well as reducing acute mucositis, to improve long-term dysphagia.