Thanks for the query.
After removal of mirena
withdrawal bleeding can occur.
The tissue you mentioned could be endometrial tissue, which might have shed after removal of mirena.
As there is no continuous shedding, no need to worry.
After removal of mirena it will take some time for regularization of hormonal
So that may be responsible for this shedding.
Which will be possibly corrected soon.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429