Are Restylane injections the solution for a vertical forehead indentation? Is it a costly procedure? (Photo)

You likely have en coup de sabre which is a localized form of scleroderma/morphea. If it is stable (not growing or changing), then injecting fillers in the indentation can be quite effective and I have treated a number of people this way with good success. The hyperpigmentation can be treated by your dernatologist with various fading agents including ideally a modified Kligman's formulation. Most importantly, seek a highly trained physician injector (e.g. dermatologist) for optimal results and safety.

But you most likely have is an immunologic disorder within an appearance called Morphoea en coup de sabre. It is a condition where there is some slow progression and loss of fat in the forehead which continues into the scalp. In my experience, fat grafting has helped such patients a great deal, making them look much more normal and smooth. I hope this helps in good luck from New York City Plastic Surgery.