About Six Months Ago I Tripped And Fell And Hit

About six months ago I tripped and fell and hit my forehead very hard. It was swollen and painful. A CT scan and MRI found nothing conclusive, though the MRI did indicate that I had an arachnoid cyst on my brain which was not connected to the impact at all. The swelling and black eye was gone in about two weeks and while it remained sensitive it caused no issues. However, this last week, the location of the impact has now developed a large lump on my forehead. Is this anything to be concerned with? It is sensitive and painful to the touch, but I don't seem to have any other issues.