Yin-yang sign on magnetic resonance imaging in a child with left frontal arterio-venous malformation and foot drop

We report an 8-year-old girl who presented with acute right foot drop with preserved reflex following minor trauma. brain magnetic resonance imaging showed a large pial arterio-venous malformation (avm) over the left frontal paramedian convexity with a large varix draining into the superior sagittal sinus. on post-contrast t1-weighted imaging,the avm showed a swirling pattern with sharply marginated outer hypo-intense area and inner hyper-intense area reminiscent of the chinese yin-yang symbol. a partially thrombosed varix in an avm nidus was suspected which was confirmed on histopathology following resection. unilateral foot drop with preserved reflex is one of the rare clinical presentations of a frontal paramedian avm. yin-yang sign is a unique magnetic resonance imaging finding suggestive of a partially thrombosed avm. © 2013-ios press and the authors.