On the map at coordinates 40.698012, 8.544684 there is a crossroads between the Rizzeddu-Gioscari and Mascarello local roads (from East to West) and Scala di Gioscari (from South to North). The Scala di Gioscari local road seems to be able to continue north, to then join up with the Piandanna road. 
In reality, after about 400 m. the road stops in front of a private villa and to reach Piandanna road it is necessary to return to the crossroads and go down the Mascarello local road.