Fragments of thickened, irregular cystic structure composed of dense, hyalinized fibrocollagenous and fibrofatty tissue. The synovial lining is markedly ulcerated, with the luminal surface extensively covered by an organizing fibrinous exudate and clotted blood. The underlying stroma exhibits florid granulation tissue containing proliferating capillaries, reactive fibroblasts, and a chronic inflammatory infiltrate of neutrophils, lymphocytes, plasma cells, and histiocytes. Areas of interstitial hemorrhage are seen. No evidence of specific granulomas. No evidence of atypia or malignancy.
Right knee mass at the anterior medial aspect, identified on ultrasound as a 2x3x4 cm turbid fluid collection with surrounding soft tissue edema (suggestive of a hematoma or abscess), for which an excisional biopsy of the subpatellar bursa was done.
The specimen consists of two soft tissue masses. The first mass measures 5 x 3.5 x 2.8 cm and shows a cyst measuring 4 x 3 cm, which is filled with yellowish fluid. The second mass measures 2.3 x 1.8 x 1.5 cm and is grey in color.
Right knee mass (sub-patellar bursa), excisional biopsy: