[Incidental meningioma].

Intracranial tumors are accidentally discovered during operations for neurosurgical diseases, such as head trauma or cerebral aneurysm. Furthermore, in the autopsy specimen, intracranial tumors which had not been recognized before the patient's life are sometimes found incidentally. Those tumors are; meningioma, glioma, pituitary adenoma, and so forth. Among these instances, meningioma seems to be the most frequent. In this paper, the authors discussed five cases of asymptomatic meningiomas found unexpectedly, referred as "Incidental Meningioma." Incidental meningioma listed up here are five out of 38 clinical cases with intracranial meningioma which authors experienced during recent twelve years in our hospital. In 480 autopsy cases in our hospital in the same period, there was only one case with which incidental intracranial tumor was detected. This incidental tumor was index-finger tip sized parasagittal meningioma. This was not included in this series. These 5 clinical cases were composed of all women ranging in age from 48 to 72 years. Three of them were discovered during aneurysm surgery, the other one was found during the evacuation of acute subdural hematoma. The remaining one case (Case 5) was demonstrated intracranial meningioma unexpectedly by CT scanning. The size of those tumors were ranged from 7 to 20 mm in diameter except Case 5. In Case 5, tumor size was about 30x40 mm in diameter. The localization of those tumors were; three convexity, one pterion, and one falx meningiomas. Positive findings referable to those tumors at ancillary neuroradiological examinations, were shown only in one case (Case 2) with the exception of Case 5 retrospectively. That was abnormal calcified shadow in frontal bone at the right side in Case 2. The histological nature of them was various, but psammomatous type belonging to transitional meningioma was worthy to note, because such a type was relatively rare in our total cases. Incidental tumors seemed to be relatively rare in cases with cerebral aneurysm. In our series comprising 747 operated cases for cerebral aneurysm, there were 5 cases with incidental tumor (0.67%). Three of these 5 cases were incidental meningioma which were listed up in the paper. In all cases with incidental meningioma, except for Case 5, there were no definite feeding arteries, and they could be easily extirpated, with uneventful recovery.