There is a reason why the new abscess is remote from the old external opening, as this is probably the site of a new fistula.

Which imaging modality do you use to follow up these patients? MRI has been shown to be the most accurate and the use of this might delineate tract anatomy better and inform you of the extent of the trapped sepsis.

New abscess may be an ano rectal abscess independent from previous fistula or it may be the extension from previous fistulous track, may be in anatomical spaces like Ischeo rectal, Pelvi rectal or post anal space etc. though it always advisable to get an MRI done to understand the disease in such cases but as for as drainage is concerned we always prefer separate incision.Use of seton/Ksharsutra may help.

I agree with an accurate study of pelvic area by a dedicated MRI. Also, EUS may be of help. After having obtained a detailed picture, the best method of drainage may be chosen (seton is preferred). Once abscess has been removed, anti-TNF alpha therapy may be of help being fistulizinc Crohn's disease an indication to this treatment.

I also prefer MRI imaging followed by drainage via seton. In complex fistulas you can leave the seton for several months. The major aim is to avoid surgery near the sphincter, as many patients will undergo multiple operations and the preservation of sphincter function is crucial for their QoL.