Fluid accumlation in breast follwing breast ca and lumpectomy. shows up on cxr 4 months after lumpectom. size is 5 x 7 cm. why?

Resifual hematoma: When a lump ectomy is performed a good dissection goes along a radial incision from near nipple outward, Skin flaps are raised and a wedge of breast tissue extends from just below skin to pectoralis fascia. Cloure is accomplished in layers (3) to close the defect created. If not closed tightly a hematoma can arise and partially solidify showing up on follow up mammo and CRX.

Probably a seroma: What you are describing is probably a seroma - a pocket of fluid in the space where the tissue used to be prior to tumor removal. Sometimes the tissue doesn't fill in the gap and fluid accumulates. It may decrease over time, but if it bothers you you can see your surgeon to have the fluid aspirated.

Possibly seroma: This is probably fluid collection or seroma in the resection cavity, especially if you also received radiation therapy. However, CXR is not the imaging modality of choice to diagnose this condition. I would suggest to see your breast surgeon, get an ultrasound to confirm the diagnosis and if there are symptoms or other indications an aspiration may be considered.