Intracranial meningiomas following low-dose irradiation to the head.

Earlier reports have suggested that low-dose ionizing irradiation might be involved in induction of intracranial meningiomas. One of the problems in evaluating irradiation-induced neoplasms is the belief that these tumors have no distinguishing features to indicate their etiology. In an attempt to identify such features in meningiomas following irradiation, a group of 42 post-irradiation meningiomas (PIM's) has been compared with a group of 84 non-PIM control meningiomas. These 42 PIM's included all the intracranial meningiomas diagnosed at the Hadassah University Hospital during the years 1952 to 1981 in individuals treated in childhood with low-dose x-ray therapy for tinea capitis. Although the individual PIM does not seem to differ from a "spontaneous" meningioma, this study indicates that PIM's as a group have distinct characteristics, namely, their location at the site of maximal irradiation, and features suggesting rapid growth and aggressive biological behavior. There was a significantly higher number of calvarial tumors (p less than 0.001), a high proportion of multiple meningiomas, a higher recurrence rate following apparent complete excision (p less than 0.02), and an increased number of histologically malignant meningiomas (p less than 0.01). The demonstration of features that distinguish PIM's from meningiomas of other etiology supports the suggestion that low-dose ionizing irradiation was involved in the pathogenesis of these tumors.