This photo shows secondary cranial fracturing that occurred due to a gunshot.  "The cerebrospinal fluid surrounding the brain absorbs the force of the blast distributing shock waves throughout the endocranium. The resulting pressure causes this kind of fracturing from the inside out" (OsteoInteractive).

Photo courtesy of OsteoInteractive at http://www-medlib.med.utah.edu/kw/osteo/index2.html