Diagnosis of a growing radiation-induced skull lesion in a patient: an unusual scar.

New lesions arising from within an area of previous irradiation often present a diagnostic dilemma, with new malignancy or metastasis of particular concern. The authors report a case of reactive fibroblast proliferation emerging from a previous radiation field and presenting as a growing lesion of the frontal and parietal skull. Following complete gross resection of the skull lesion and histopathological analysis, it was discovered that this lesion consisted of dense fibroblast proliferation with areas of osteonecrosis. This unusual reactive phenomenon offers a novel differential diagnosis for a new contrast-enhancing lesion in a region of previous radiation.