Abstract:   Objective To analyze the magnetic resonance imaging (MRI) manifestation characteristics of radiation-induced brainstem injury in patients with nasopharyngeal carcinoma (NPC) after radiotherapy.Methods Brain MRIs from 37 patients with NPC who developed radiation-induced brainstem injury after radiotherapy were reviewed.The study analyzed imaging sequences included T1-weighted image (T1WI)，T2-weighted image (T2WI)，fluid attenuated inversion recovery (FLAIR) and enhanced scanning imaging to define the site，range，signal strength and enhanced form of the lesions with radiation-induced brainstem injury. Results Among the 37 patients，19 had lesions in pons; 1 in midbrain; 3 in medulla oblongata; 6 in pons and midbrain; 5 in pons and medulla oblongata; 3 in pons，midbrain and medulla oblongata. All lesions showed hypo-or iso-intense signal on T1WI，and hyper-intense signal on T2WI.With contrast enhanced scanning，9 cases did not show enhancement，28 cases showed marked enhancement which included 12 cases with homogenous patchy enhancement and 16 cases with heterogeneous ringed and patchy enhancement. Conclusion MRI can clearly show the lesions of radiation-induced brainstem injury in NPC patients after radiotherapy，which is available for clinical diagnosis.

Key words: Nasopharyngeal carcinoma (NPC), Radiation injury, Brainstem, Magnetic resonance imaging (MRI)