techniques to bring attention to one part of a line drawing?

[bik]

What if you just changed the color of the black lines – make the lines in that area red or whatever color would stand out and be appropriate?

You could make a circular selection of the area, copy and paste to get a new layer, and make the new layer have a Layer Style > Color Overlay. The "white" areas would need to be knocked out/transparent so that the color overlay would just be the lines.