This video provides a detailed microscopic analysis and discussion of a case diagnosed as Giant Cell Tumor of the Tendon Sheath (GCTTS), also known as localized tenosynovial giant cell tumor. The speaker initially identifies the tumor by the presence of dense collagen and characteristic multi-nucleated, osteoclast-like giant cells. The lecture clarifies that GCTTS is primarily a deep soft tissue entity, usually arising from the tenosynovium. A key takeaway is the distinction between the giant cells (which are reactive) and the true neoplastic cell—a mononuclear histiocyte with abundant, eccentric cytoplasm. Crucially, the video focuses on the near-pathognomonic finding of hemosiderin rings or halos encircling the tumor cells, which are colloquially referred to as "ladybird cells."
Giant Cell Tumor of the Tendon Sheath (GCTTS) - Localized Type
(0:04) Initial Assessment: The case presents as a purple, multiloculated lobule with a background of dense collagenous tissue.
(0:28) Key Histological Finding: The presence of multi-nucleated, osteoclast-like giant cells strongly suggests a differential diagnosis of Giant Cell Tumor of the Tendon Sheath (GCTTS).
(0:47) Clinical Context: GCTTS (or localized tenosynovial giant cell tumor) is usually a deep soft tissue entity, typically attached to the tendon sheath on the hands, fingers, feet, or toes. It rarely involves the dermis; therefore, if a test slide shows this morphology attached to dense connective tissue without overlying skin, GCTTS is the expected answer.
(2:23) Identifying the Neoplastic Cell: The osteoclast-like giant cells are not the neoplastic component; they are reactive. The true neoplastic cell is the mononuclear histiocyte, characterized by abundant cytoplasm and an eccentric nucleus, giving it a plasmatoid or rhabdoid appearance. These cells can be mitotically active.
(2:50) Other Features: The tumor architecture includes dense collagen, variable inflammation, areas of discohesion (cells appearing to fall apart), and often foamy histiocytes (xanthoma cells).
(3:16) Hemosiderin Importance: Hemosiderin is usually present, sometimes abundantly, and serves as a vital diagnostic clue.
(3:40) Pathognomonic Feature (Ladybird Cells): Hemosiderin frequently creates distinctive rings or halos around the periphery of the tumor histiocytes. This feature is also referred to as "ladybird cells" (due to a potential resemblance to a ladybug) and is considered nearly pathognomonic for GCTTS.