Delayed Migration of Onyx Embolic Agent after Preoperative Embolization of an Arteriovenous Malformation in a Pediatric Patient: A Case Report and Review of the Literature.

Introduction: Brain arteriovenous malformations (AVMs) are increasingly being treated with Onyx liquid embolic agent (Onyx, Medtronic, Inc.). The phenomenon of delayed Onyx migration is not well documented in the literature. Moreover, the clinical presentation associated with Onyx migration is not well understood.

Case presentation: A pediatric patient with a history of neonatal seizures was referred to our institution upon experiencing daily headaches with photophobia, phonophobia, and sleep disturbance. Cerebral angiography revealed an AVM of the medial left cerebellar hemisphere. Preoperative embolization with Onyx liquid embolic achieved 25% closure of the AVM nidus. Upon developing worsening headaches the following day, new perinidal parenchymal edema was revealed on MRI, and urgent angiography demonstrated delayed migration of Onyx into the venous drainage. The patient underwent emergency resection of the AVM due to the risk of hemorrhage resulting from venous outflow obstruction.

Conclusion: Our report and literature review demonstrate that while the delayed, unexpected migration of Onyx embolic material has been alluded to in a handful of papers, this phenomenon is not well documented. Future research is needed to understand the frequency of delayed Onyx migration from brain AVMs and the possible clinical presentations to look for. The sudden development of headaches and other signs of perilesional edema, in particular, should prompt repeat angiographic examination due to the possibility of delayed liquid embolic migration.