I read Tracy's post with interest as I, just last week, had a mom come in for
a 48 hr. follow-up visit with this same condition.
<< She has what she
 describes as an extra breast under her arm. There is no supernumerary nipple.
>>  In all my years of helping moms, I hadn't seen this before.  This mom was
breastfeeding (they aren't all, hospital checks for all moms) and stated that
this swelling began when her milk started coming in.  When she showed it to
me, I was shocked, it was, as Tracy described, with well-defined borders,
looking for all the world like a small breast, but with no nipple.  I
consulted our residents before sending her home, since I'd not dealt with it
before.  They were not concerned.  Personally, I'd like to know more about it.
I didn't know what to tell her about when it would resolve (or if or to what
degree) and I have an inquiring mind, I'd just like to know!  So those of you
with experience or info on this, please pass on to the list.  I have heard of
"auxiliary breasts" but thought they had nipples!  TIA.

Marsha Puckett RN, IBCLC in wonderfully warm and colorful central Indiana