Elderly Dog with bony lump on one side of his head......?

My 11 and a half yr old Border Collie has a hard bony lump on one side of his head which has appeared recently. For some while now his head seems to have been getting bonier and almost feels as if it is changing shape. He doesn't seem to be in any distress and is behaving normally. I've made a vet's appointment for him next week but just wondered if anyone else had encountered this in an ageing dog? Many thanks.