Pitfalls of Preoperative Embolization for Meningiomas: A Case Report on Occult Anastomosis Between the Middle and Posterior Meningeal Arteries

Preoperative embolization facilitates meningioma resection by reducing intraoperative bleeding. The middle meningeal artery (MMA) is frequently targeted; however, the presence of occult anastomoses between the MMA and the posterior meningeal artery (PMA) and their potential involvement in ischemic complications remain poorly understood. A 61-year-old woman with no prior medical history was incidentally found to have a right parietal extra-axial tumor on magnetic resonance imaging (MRI). She was neurologically intact upon admission, but perifocal cerebral edema was observed surrounding the tumor, which measured approximately 33 mm × 27 mm × 22 mm. Given the patient's condition and life expectancy, tumor resection was planned, preceded by preoperative embolization to minimize intraoperative bleeding. Angiography identified the parieto-occipital branch of the right MMA as the primary feeder, and superselective angiography showed no evidence of anastomoses. Microparticles were injected into the MMA; however, immediately afterward, the patient became comatose and exhibited transient dysarthria. Postembolization angiography revealed retrograde visualization of the vertebrobasilar system through previously undetected MMA-PMA anastomoses. Subsequent MRI confirmed extensive ischemic lesions in the posterior lobes, hippocampus, cerebellum, and thalamus. The patient later developed right hemiparesis, clumsiness, dysarthria, and memory impairment, necessitating rehabilitation. While motor symptoms resolved within 10 days, memory disturbance persisted but improved with therapy. This case highlights the risk of ischemic complications due to occult MMA-PMA anastomoses, which may become functionally significant only during embolization, even if undetectable on preprocedural superselective angiography. This dynamic vascular response underscores the need for heightened vigilance in preoperative embolization planning. Clinicians should consider the possibility of latent anastomoses emerging intraoperatively, necessitating careful embolic agent selection and procedural modifications to minimize complications. Recognizing this risk may enhance patient safety and optimize embolization strategies for meningioma treatment.