It is not a question of wether you need a 50 ohm impedance somewhere or not. If you have a trace, no matter where in the chain it is, and the length of that trace is more than a couple of millimeters it should have 50 ohm impedance.
Please understand that this i not a 50 ohm resistive element, but rather a characteristic of the trace itself. You can read more here: Wikipedia_Characteristic_Impedance.
/Fredrik