Galactoceles (and the lactating breast in general) can be nightmare lesions for sonologists. The wide variation in appearance can be very confusing and to further complicate issues, no one wants to conservatively manage or downplay an enlarging breast lesion in a lactating patient.
As a general rule, very careful follow up imaging should be used almost without exception and this is one place in radiology where I even say in the report that follow up should be done at the same site and even on the same ultrasound machine if possible. Without exception, the radiologist should view these images in real-time.
Most of these lesions clear up with conservative management, as in this case. The fistula is messy, but otherwise the lesions are rarely difficult to manage.
The teaching point is this is a complication of intervention on a galactocele, but its very rare. I have seen 2 in more than 2 decades of breast imaging.
Don't assume that lesions that develop in the lactating breast are all galactoceles. If the lesion enlarges, stick a needle in it. Meticulous careful follow up is mandatory.