A Honor Society of Nursing (STTI) answered. External hernias are caused by part of an organ pushing through an opening or weakness in the abdomen wall. An internal hernia is caused by part of an organ pushing into an opening or weakness in the wall of another organ within the same cavity.External hernias are also brought about by pressure or strain placed on openings or weak spots on the abdominal wall.n internal hernia is caused by part of an organ pushing into an opening or weakness in the wall of another organ within the same cavity.