If high-grade dysplasia is found in a patient with chronic ulcerative
colitis and a bowel resection is performed, how likely is high grade
dysplasia (neoplasia) to recur in the remaining colon?

Hi -  The risk of high grade dysplasia and colon cancer in ulcerative
colitis has been well documented (see links in General information
below).  Prophylactic colectomy is advocated to remove all colonic
tissue to prevent further evolution of dysplasia and/or cancer.  The
amount of colon which is removed is variable between procedures (ie
some procedures spare sections of the colon near the anus in order to
provide the patient with continence).  Any leftover mucuosal tissue
from the colon has some potential to develop into dysplasia and/or
cancer.  Ileoanal anastamosis appears to have the largest number of
case reports of anal canal cancer developing post surgery (still
described as rare, however).  The studies, along with brief summaries,
which I found on the subject are listed below.  In general, it appears
that the risk ranges from 0/40 to 3/46 in the larger studies.

A Swedish study on 46 individuals with UC who had ileorectal
anastamosis performed showed 3 patients who subsequently developed
dysplasia
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2055142&dopt=Abstract

A small French study (16 patients) suggesting that dysplasia can recur
in patients with an ileocecal anastamosis:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7813864&dopt=Abstract

There are four cases of anal cancer described in patients who
underwent a colectomy with ileoanal anastamosis (small intestine
connected to the anus with the entire colon removed) prophylactically
for ulcerative colitis:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12068206&dopt=Abstract

Another case study reporting a case of anal cancer in a patient who
had an ileal-pouch anal anastamosis for UC
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12004221&dopt=Abstract

A 30-year follow-up study on patients who underwent a continent
ileostomy resection for UC and found no cases among 40 patients of
high-grade dysplasia:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12006923&dopt=Abstract

A 6-year Czech follow-up study suggesting that UC patients post
resection have the same risk as the rest of the population:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11789007&dopt=Abstract

General Information on UC and colon cancer:

A reasonable page describing ulcerative colitis, the increased risk of
colon cancer in individuals with UC (particularly if the entire colon
is involved - .5-.8% per year risk), and a discussion of the surgical
options.  High grade dysplasia is considered a reason for prophylactic
colectomy.
http://www.guideline.gov/VIEWS/summary.asp?guideline=2193&summary_type=brief_summary&view=brief_summary&sSearch_string=

A study examining the link between high-grade dysplasia and cancer,
suggesting that 1/3 of patients with UC and high-grade dysplasia will
have cancer diagnosed at the time of surgery:
http://www.eboncall.co.uk/CATs/2364.htm

Let me know if you would like any clarification or expansion of my
explanations.

synarchy

Thanks for being very specific.  You gave me the information I was looking for.

I assume the type of colectomy about which you ask your question is
indeed a near-total colectomy: to remove only the segment involved
with dysplasia would be considered  inadequate in most situations. So
the answer above correctly refers to ileo-anal anastomosis, which
means the entire colon is removed from the end of the small intestine
(ileum) to the anus. When such an operation is performed, there are
many issues to consider: the way absolutely to prevent recurrance is
to remove the entire colon, creating a permanent ileostomy (intestine
coming to the skin, contents into a bag.) To avoid that, lesser
operations are done; the more colon (rectum) that remains, the better
the chance of  tolerable bowel control and frequency of stool --  but
the greater the risk of neoplasia. With the ileoanal procedure, a
pouch is created of small bowel, and hooked to the anal canal; since
the control muscles remain (sphincters) theoretically bowel control is
good.  Actual results can vary from a few to a lot of bowel movements
per day, with anywhere from no problems with control, to some leakage
(especially at night), to enough problems that ileostomy is
preferrable. Infections in the pouch (pouchitis) are not rare. Results
of surgery are best when it's done by a surgeon with lots of
experience with the procedure. When any amount of colon remains, the
key is regular surveillance, meaning passing a scope and doing
biopsies. If and when dysplasia is seen, then the remaining colon
tissue may need to be removed.