Osteoradionecrosis of the upper cervical spine: MR imaging following radiotherapy for nasopharyngeal carcinoma.

Purpose: To document the MRI appearances of radiation-induced abnormalities in the cervical spine following treatment for nasopharyngeal carcinoma (NPC).

Methods: Patients with radiation-induced abnormalities in the upper cervical spine were identified from a retrospective analysis of reports from patients undergoing MRI follow-up. Imaging and clinical records of these patients were reviewed. Symmetrical distribution of abnormalities at C1 (anterior arch+/-adjacent aspect of the lateral masses) and C2 (dens+/-body especially with a characteristic horizontal rim of marrow preservation above the inferior endplate) were considered typical for osteoradionecrosis (ORN).

Results: Abnormalities of C1/2 were identified in 9/884 (1%) patients. The MRI distribution of abnormalities was typical for ORN in four and atypical in five patients. Abnormal soft tissue was present in the atlantoaxial joint in eight patients, forming a florid mass in six. This soft tissue was in direct continuity with the posterior nasopharyngeal wall ulceration via the retropharyngeal region. The final clinical diagnosis was ORN in eight, five of whom had clinical factors which suggested infection could have played a contributory role, and osteomyelitis in one patient. All patients had undergone additional radiotherapy treatment comprising of brachytherapy (7), stereotactic radiotherapy (1) or radiotherapy boost (2) and three had undergone nasopharyngectomy.

Conclusion: ORN of the upper cervical spine following radiotherapy for NPC is more common than previously suspected and is seen in patients with additional treatment, especially brachytherapy. MRI features are often atypical and a contributory role of infection in the development of some cases of ORN is postulated.