A 28-year-old woman presents with a 6-month history of progressive swelling and pain over the distal femur. Plain radiographs show a lytic lesion in the epiphyseal region with a soap-bubble appearance. Which investigation is most appropriate to confirm the diagnosis of giant cell tumor of bone?

Explanation

## Diagnosis of Giant Cell Tumor of Bone ### Role of Core Needle Biopsy **Key Point:** Histopathological examination via core needle biopsy is the gold standard and most specific investigation for confirming giant cell tumor (GCT) of bone. **High-Yield:** GCT diagnosis cannot be reliably made on imaging alone. The characteristic histological finding is the presence of multinucleated giant cells admixed with mononuclear stromal cells and hemosiderin deposits. ### Imaging Findings (Non-Specific) | Imaging Modality | Findings | Utility | |---|---|---| | **Plain X-ray** | Eccentric lytic lesion in epiphysis/metadiaphysis; soap-bubble or honeycomb pattern | Initial screening; shows location and bone destruction | | **CT** | Better cortical detail; shows matrix mineralization | Surgical planning; NOT diagnostic | | **MRI** | T1: intermediate signal; T2: mixed signal with hemosiderin; fluid-fluid levels | Best for soft tissue extent and surgical planning; NOT diagnostic | | **Bone scan** | Increased uptake | Non-specific; indicates osteoblastic activity | ### Why Biopsy is Essential **Clinical Pearl:** The radiological "soap-bubble" appearance, while classic, is not pathognomonic. Differential diagnoses (aneurysmal bone cyst, chondroblastoma, osteoblastoma) can mimic GCT on imaging alone. 1. Confirms multinucleated giant cells (diagnostic hallmark) 2. Rules out mimics (ABC, chondroblastoma, osteomyelitis) 3. Guides treatment decisions (curettage vs. wide resection) 4. Core needle biopsy is preferred over open biopsy to avoid tumor seeding **Mnemonic: GCT Diagnosis — BIOPSY FIRST** — Before Imaging, Open surgery, Prognosis — Start with histology. [cite:Rockwood & Green's Fractures in Adults Ch 29]