Seroma following lumpectomy in breast cancer:

   
The ultrasound video clip of the breast above, shows a typical seroma of the breast following lumpectomy (removal of breast lump) and is a common sequel to such breast surgeries. The presence of particulate matter in the cystic collection (fluid) in the dead space left following breast lump removal, is an indicator of the presence of hemorrhage into the cavity. Most surgeons are of the opinion that larger seromas are formed following removal of large breast lumps and particularly following axillary lymph node dissection.
    In the ultrasound video clip above note the motion of significant particles within the serous fluid. Presence of particles, mural nodules, septae are all evidence of hemorrhage following breast lumpectomy. The color Doppler ultrasound image below shows the absence of significant vascularity around the walls of the seroma, implying lack of wound/ wall infection or inflammation.

In the absence of history of breast surgery, such cystic lesions can confound the sonologist and lead to error in the diagnosis of breast seroma.
More information and ultrasound images of this case can be had at:
http://www.ultrasound-images.com/breast.htm#Breast_seroma_following_lumpectomy_for_breast_carcinoma

Breast ultrasound (google books)
(an excellent description of sonography of breast seroma)

Study of breast seroma