This video provides a detailed pathological examination of Tenosynovial Giant Cell Tumors (TSGCT), covering the spectrum from the localized form (Giant Cell Tumor of Tendon Sheath, GCTTS) to the diffuse, locally aggressive form (Pigmented Villonodular Synovitis, PVNS). Lecturer Jared Gardner emphasizes the importance of recognizing the tumor by its background features—mononuclear histiocytes, foamy cells, sclerotic stroma, and hemosiderin—as the characteristic osteoclast-like giant cells are often sparse or absent. Key diagnostic features highlighted include the distinctive "hemosiderin halo" pattern (Ladybird cells), brisk mitotic activity (which should not be confused with malignancy), and the cystic/discoesive growth patterns. The lecture also addresses clinical pitfalls, such as the tumor’s occasional PET avidity and potential confusion with rhabdomyosarcoma due to morphology and immunohistochemical staining (Desmin).
Tenosynovial Giant Cell Tumors: Diagnosis Without Giant Cells
0:02 The Spectrum of TSGCT: Tenosynovial Giant Cell Tumors (TSGCT) are on a spectrum, including the small, localized Giant Cell Tumor of Tendon Sheath (GCTTS) and the more diffuse, infiltrative Pigmented Villonodular Synovitis (PVNS).
0:36 Distinction: GCTTS and PVNS look microscopically identical at high power but are distinguished by their size, growth pattern (localized vs. diffuse/infiltrative), and location (extra-articular vs. intra-articular).
1:09 Key Diagnostic Challenge (Takeaway): Pathologists must learn to recognize TSGCT even when giant cells are sparse or absent, relying on background features.
1:48 Neoplastic Cells: The actual neoplastic cells are the mononuclear histiocytes/epithelioid cells scattered in the background; the giant cells are secondary, recruited cells.
2:29 Sclerotic Stroma: A hallmark feature is the presence of the neoplastic cells embedded in a very dense, sclerotic, and hyalinized background.
2:47 GCTTS (Localized Form): Typically a small, circumscribed nodule found on the distal extremity (hands/fingers).
3:20 PVNS (Diffuse Form): More infiltrative, usually found in large joints (knee is the most common site), and associated with local aggressiveness.
4:38 Foamy Histiocytes (Xanthoma Cells): The presence of foamy histiocytes is a common and useful diagnostic clue, especially in giant cell-poor cases.
5:24 Pathological Pitfall: Mitotic Activity: TSGCT can have brisk mitotic activity (up to 10-20 mitoses per 10 HPF). This high rate does not imply malignancy in this specific tumor context.
7:31 Hemosiderin Deposition: Hemosiderin is usually abundant in both forms (giving PVNS its "pigmented" name) and is a key diagnostic clue.
8:21 The Hemosiderin Halo (Key Takeaway): The most characteristic feature is hemosiderin deposited in a "wreath" or "halo" around the eccentric nucleus of the large epithelioid histiocytic cells (often called "Ladybird cells").
10:17 Growth Pattern: Discohesive Pools: Histiocyte-like cells aggregate in clusters that become discohesive, forming cystic spaces or "swimming pools" filled with floating histiocytes.
11:46 Clinical Pitfall: PET Avidity: TSGCTs are often PET avid due to their mitotic activity, which can lead to misdiagnosis as metastatic cancer in patients with a history of malignancy.
14:09 Immunostaining Pitfall: The neoplastic cells are CD68 positive but can show Desmin expression, which, combined with the eccentric (rhabdoid) morphology and mitotic activity, risks confusion with rhabdomyosarcoma.
15:10 Clinical Prognosis: While GCTTS recurs locally but is non-destructive, PVNS is highly problematic due to a high tendency for local recurrence and destructive, locally aggressive behavior.
15:43 PVNS Architecture: When intra-articular, PVNS forms large villus or frond-like papillary projections lined by synovium, creating a shaggy gross appearance.
17:34 Infiltrative Nature: PVNS is invasive, spreading from the joint space into adjacent soft tissue, making complete surgical clearance difficult and contributing to high recurrence rates.