Cerebral Arteriovenous Malformation Deep Draining Veins Not Observed on Preoperative Angiography Identified on Postoperative Angiography.

Postoperative digital subtraction angiography (DSA) is the gold standard for establishing a cure of an arteriovenous malformation (AVM) after treatment. The incidence of residual AVM identified on postoperative DSA ranges from 1.8 to 11%. Although this is important for finalizing the treatment of AVMs, postoperative DSA rarely shows new findings that were not previously identified on preoperative imaging. We present a unique case where we identified residual AVM nidus on immediate postoperative DSA that drained into two deep veins that were not evident on preoperative DSA and increased the AVM grade from Spetzler-Martin grade II to III. To our knowledge, this finding has not been previously reported in the literature. We resected the residual AVM nidus identified on postoperative DSA, leading to an angiographic cure. The patient demonstrated a postoperative right-sided supplementary motor area syndrome that resolved over time with therapy. She made a complete functional recovery by her one-month follow-up appointment.