Histopathologic analysis of craniofacial arteriovenous malformations following Onyx embolization

Ethylene-vinyl alcohol copolymer (Onyx) has been proposed as a suitable alternative embolic agent in the management of craniofacial arteriovenous malformations (CFAVM). Short-term efficacy studies have demonstrated promising results with good nidus penetration on post-treatment angiography. This article reports the histopathologic findings of direct vascular recanalization with Onyx at the time of surgical resection. A retrospective review of eight patients who underwent Onyx embolization followed by surgical excision for CFAVM was performed. The surgical specimens were evaluated for the presence of recanalized blood vessels in the embolic cast material and inflammatory changes. A total of 8 patients (mean age 31 years, range 15–57 years) underwent 25 CFAVM embolization and 16 surgical specimens were taken. The time period between initial Onyx embolization and surgery ranged from 12 months to 108 months. Onyx was identified in all of the 16 specimens at the time of resection. Recanalization was identified in 12 of the 16 specimens (75%). Chronic inflammatory changes were present in 13 of the 16 specimens (81.25%) ranging from mild (8) and moderate (4) to severe (1). Giant cells were present in 15 of the 16 specimens (93.75%). Staged Onyx embolization has been reported as clinically efficacious in the management of CFAVM with permanent occlusive properties. Recanalization was commonly seen in this patient cohort as early as 12 months after initial endovascular treatment. Further studies are needed to confirm these findings to evaluate the permanence of Onyx as single agent management for CFAVM.