Mucosectomy simply means removing the mucosal layer, not sectioning the entire bowel wall. So, in this case, a 3cm cuff was reduced to 2cm and the mucosa was "stripped." Sounds simple, but far from it. Mucosectomy requires a lot of technical skill to avoid damaging the nerves at the dentate line (transition zone between the rectum and the anal canal). It is not like peeling a banana, but involves injecting fluid under the mucosa and carefully dissecting it away. If done completely, the mucosa will not grow back. But remnants left behind could potentially repopulate the cuff. Generally, if a mucosectomy is performed, a hand sewn anastomosis is required, because you need the intact rectum to use the stapler. I say generally because one member here once said she had a stapled anastomosis, but also had a mucosectomy. You also cannot have no retained cuff without a hand sewn anastomosis. But, having a hand sewn anastomosis does not mean you automatically had a mucosectomy. I am one who has rectal mucosa, but had a hand sewn anastomosis. Could be because it was about 20 years ago and the douple stapled technique was not the standard.
As to the "reach" issue, men tend to have deep and narrow pelvic outlets, and women tend to have a wide and shallow pelvic outlet. This is by design, since only women need to pass something the size of a baby's head.
The combination of a male type pelvis and a shorter mesentery may make a j-pouch impossible, or require technical "tricks" to lengthen the reach. These can include a longer cuff, vascular manipulation, or the use of an s-pouch instead of a j-pouch configuration.
I don't know if this situation was present for your son. It could be his age and just not enough room to work. I just do not know. Certainly his surgeon could tell you?
Hope this helps clarify.
Jan