[MR imaging of osteoradionecrosis of the mandibula following radiotherapy for head and neck cancers].

Magnetic resonance (MR) images of 13 patients with osteoradionecrosis of the mandibula were analyzed. Abnormalities were noted in all patients and could be classified into three groups. In nine patients, MR signals were homogeneously low in intensity on both T1 weighted images (T1WI) and T2 weighted images (T2WI), suggesting fibrosis of bone marrow. These nine patients had suffered radiologically and/or clinically overt osteoradionecrosis more than ten months previously, and inflammatory symptoms had settled down by the time of MR study. Two patients showed low signal intensity on T1WI and an area of inhomogeneous high intensity in a diffuse area of low signal intensity on T2WI, suggesting acute inflammation in the irradiated fibrous bone marrow. Both patients suffered pathologic fracture due to osteoradionecrosis and showed severe inflammatory symptoms at the time MR study. In one of the two patients, these pathologic changes were confirmed in surgically excised mandibulectomy specimens. The other two patients showed homogeneous low signal intensity on T1WI and high signal intensity on T2WI, a finding that may be due to slight inflammation. However, in one of the two patients, this signal feature possibly indicated loose fibrosis with marked cellularity.