Abstract

PURPOSE:

Dysfunction 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 METHODS:

Twelve 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.

RESULTS:

T1-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 (R(2)=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).

CONCLUSIONS:

These 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.