This was discussed at some length earlier, but I don't remember where or when.
But the essence of the story is that in 1908, the B&O was attempting to replace its original (1885) Susquehanna bridge with the present structure, while still maintaining traffic over it. Unfortunately a coal train derailed Sept. 23, 1908, and demolished one span, requiring detours over the nearby and paralleling PRR. A connection was hastily built on the west side of the river between Swan Creek on the B&O and PRR's Oakington station and, as you mention, on the east end at Perryville/Aiken. The Swan Creek-Oakington connection was particularly awkward because it was laid out in reverse -- that is, B&O trains from either direction had to reverse and back through the connection.
I believe that this operation lasted until the B&O's bridge reconstruction job was finished January 6, 1910, but am not sure. In any event, the Swan Creek connection did not last long after that, sincve it served no purpose other than the emergency detour. Likely it didn't last long enough to show up on any topo maps. I've never tried to scout the ground around there, but I'm not sure you can find any remnants of it now. At least there is nothing visible from the Amtrak NEC line or Route 40.