So the findings is the “dense” venous structure right? Well that is classic for a DVA (developmental venous anomaly). It doesn’t necessarily have to be thrombosed to be seen, just like the dural venous sinuses right. DVAs can be associated with the other finding which is the cortical small hyperdensity in the left frontal lobe - ie a small cavernous malformation.

Answer: Left frontal cavernous malformation with associated Developmental venous anomaly (aka cav mal + DVA = mixed vascular malformation (MVM))

reference: http://radiopaedia.org/articles/developmental-venous-anomaly