Peyronie’s disease is characterized by a plaque, or hard lump, that forms within the penis. The plaque, a flat plate of scar tissue, develops on the top or bottom side of the penis inside a thick membrane called the tunica albuginea, which envelopes the erectile tissues. The plaque begins as a localized inflammation and develops into a hardened scar. This plaque has no relationship to the plaque that can develop in arteries.