Hi OMB, I was re-reading over some studies I found online and I noticed this bit that you may find consoling. It is describing the type of surgery you had, an internal flap, which they refer to as a Martin's Anoplasty. If you notice, at the end of the excerpt, they say that the external part of the wound is left open. This could be the portion that you are noticing as the sensitive patch on the outside. It is also possibly what the ER surgeon saw as the open wound.
"This is a modification of Martin’s anoplasty (Figure (Figure1A1A)[1,23,24]. A midlevel stenosis is corrected by excision of the scar tissue. An undermining of the proximal rectal and anal mucosa through a transverse incision at the dentate line is performed. An internal sphincterotomy is performed if a functional component is present. The resulting flap is advanced to the distal edge of the internal sphincter near the anal verge. The vascular supply is maintained through the submucosal plexuses. The external part of the wound is left open to minimize ectropion formation."
There is a graphic too, that I can't seem to post. The link to the article is below. The graphic is down under the surgery section, labeled Figure 1. You procedure, called Martin's Anoplasty is in Column A.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2675080/