an incision parallel and a few millimeters posterior to the retroauricular fold, made to gain access to the mastoid cortex.
post·au·ric·u·lar in·ci·sion
(pōst'awr-ik'yū-lăr in-sizh'ŭn) An incision parallel and a few millimeters posterior to the retroauricular fold, made to gain access to the mastoid cortex.