Duff McKagan , the bassist of Guns n' Roses, apparently underwent sinus surgery back in December 2010. According to media reports , his sinus cavities developed significant scar tissue due to years of cocaine abuse. Sinus surgery due to scar tissue is a relatively rare indication for surgery, but required if they block sinus cavities leading to recurrent sinus infections. Cocaine abuse more typically causes other sino-nasal abnormalities especially septal perforation. Exactly w…