An arteriovenous malformation at the junction of left parietal and occipital lobes as a nidus measuring just over 3 cm diameter. Principal blood supply is from enlarged parietal and posterior temporal branches of the left MCA with some contribution from left PCA branches. No right sided supply and no external carotid supply. Venous drainage is via a large vein draining to the superior sagittal sinus and a smaller superficial vein draining to the left sigmoid sinus. No arterial flow related aneurysms. Conclusion: Left parieto occipital AVM ( Spetzler Martin Grade 3).