Purpose To discuss the relationship between radiation bone injuries and a splitting of the cortical bone in the radiation field.
Patients and methods Between January 1993 and September 1998, 53 patients with head and neck cancer received radiotherapy. The study cohort consisted of 23 patients who were followed with computed tomographic scans more than one year after radiotherapy. We evaluated clinical and computed tomographic features. Computed tomographic scanning was performed with a section thickness of 3 or 4mm. Bone images were obtained with identical window width (4000 Haunsfield units) and window level (1000 Haunsfield units). Splitting of the cortical bone was defined as disappearance of bone density in the cortical bone, showing a linear shape running parallel to the surface of the cortex.
Results Splitting appeared in 9 sites in 8 patients. All patients fulfilled UICC criteria for classifying oral cancer. Most of the patients received external irradiation with a total radiation dose of 50 or 60Gy. In all cases, splitting was found in the mandibular cortex at the site of muscle attachment, that was included in the radiation field. Appearance of bone changes in chronological order were periosteal reaction, splitting and bone necrosis.
Conclusion We speculate that splitting results from injuries to bone structure cells caused by blood flow disturbance after surgery and radiotherapy. It is suggested that such splitting can be a predictor of osteoradionecrosis.