Factor the Expression Completely $x ^ { 2 } \left( x ^ { 2 } - 4 \right) - 16 \left( x ^ { 2 } - 4 \right)$

Factor the expression completely. $x ^ { 2 } \left( x ^ { 2 } - 4 \right) - 16 \left( x ^ { 2 } - 4 \right)$