[Distinctions of petroclival meningioma with perifocal edema on adjacent brain stem]

Although the most frequent benign tumor of the central nervous system, meningioma may be associated with extensive peritumoral edema. Whereas, peritumoral edema in the brain stem along the tumor in the infratentorial region has not been given sufficient recognition. Among 44 meningiomas attached to the petrous bone, 25 cerebellopontine angle meningiomas and 17 petroclival meningiomas, peritumoral edema in the brain stem along the tumor were clearly demonstrated on T2 weighted images of MRI in three petroclival meningiomas (6.8% of all clival and 17.6% of petroclival meningiomas). Attempts were made to surgically remove all of these tumors. However, during surgery an arachnoid/pial layer between the tumor and brain stem was destroyed completely and small perforating arteries were found to be encased in the tumor at the level of the associated edema. So surgical dissection of the tumors from the brain stem was quite difficult. By attempting radical removal of the tumor in the first case, even meticulous dissections caused direct surgical damage in the brain stem due to the obliteration of small perforating vessels. In the second case, a thin layer of the tumor remnant beside the brain stem was left intentionally, but a severe damage of the brain stem also occurred due to the obliteration of small perforating vessels. In the third case, only bulk reduction of the tumor was attempted to minimize the mass effect to the brain stem and the tumor located beside the brain stem with edema and encasing the cranial nerves and the perforating arteries from the vertebrobasilar artery was left untouched. This surgical attempt caused a transient worsening of a swallowing disturbance, but was not associated with the brain stem damage in this case. In meningiomas attached to the clivus, existence of associated peritumoral edema in the adjacent brain stem on T2 weighted images on MRI may be caused by the destruction of a arachnoid/pial layer and the encasement of small perforating vessels. The attempt at tumor dissection from the brain stem at the level of the edema was very difficult and led to serious surgical complications due to direct damage to the brain stem. In such cases, the surgery should aim at achieving a simple bulk reduction and the tumor beside the brain stem with edema should be left untouched.