Two patients underwent uneventful total removal of convexity or trigone meningioma, but subsequently edema enlarged causing symptoms 3-4 weeks later. Gradual improvement was obtained by steroid administration in 1 patient and re-craniotomy in 1 patient. The histological findings in Case 1 were not confirmed, but inflammatory reaction against residual microfibrillar collagen hemostat (MCH) may have developed. The specimen from around the cyst in Case 2 showed moderate staining for vascular endothelial growth factor (VEGF). VEGF secreted by the tumor might have resulted in spread of inflammation due to MCH in the brain parenchyma. Furthermore, inflammatory reactions may have obstructed or formed a one-way communication in the inferior horn and residual cavity, resulting in malabsorption of cerebrospinal fluid. Postoperative edema with the timing in these cases is difficult to anticipate. However, the risk of this phenomenon can probably be minimized by ensuring that MCH is removed as effectively as possible after use, or by refraining from use in the brain parenchyma and by taking care to connect the residual cavity to the ventricular system, particularly if the tumor contacts a cerebral ventricle.