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< Back Dr. Sefa Giray BATIBAY Basic Tumor Biology Musculoskeletal tumours are diverse, historically classified by morphology and histology. WHO classification is the gold standard. Advances in molecular biology, cytogenetics, and sequencing improved diagnostic precision (e.g., EWS-FLI1 in Ewing sarcoma, USP6 rearrangement in ABC). Tissue of Origin Most arise from mesenchymal tissue (bone, cartilage, fibrous tissue, fat, muscle). Some from neuroectodermal cells (nerve sheath tumours, PNET). Others are secondary (metastatic carcinomas, hematologic malignancies). Benign vs Malignant Benign: No metastatic potential but may be locally aggressive (e.g., GCT, ABC). Malignant: Sarcomas (osteosarcoma, Ewing sarcoma, chondrosarcoma, soft tissue sarcomas). Borderline/atypical lesions exist (e.g., atypical lipomatous tumour). Key Biological Features Oncogenes & tumour suppressor genes: TP53, RB1, IDH mutations. Translocations: EWS-FLI1 in Ewing’s, SYT-SSX in synovial sarcoma. Microenvironment: Angiogenesis, immune evasion, stromal interactions. Invasion: Matrix metalloproteinases facilitate spread. Clinical Relevance Guides diagnosis (histology + immunohistochemistry + molecular testing). Determines prognosis (grading, staging systems). Provides therapeutic targets (e.g., checkpoint inhibitors, IDH inhibitors). Emphasises importance of biopsy strategy (always after imaging, in referral centres). Research Focus Integration of genomics and molecular diagnostics for accurate classification. Development of targeted therapies for sarcomas. Collaborative research networks (e.g., NCRI Sarcoma Clinical Studies Group in the UK). References WHO Classification of Soft Tissue and Bone Tumours, 2020 Rankin KS. Basic science of musculoskeletal tumours. MPorth, 2017 Hanahan D, Weinberg RA. Hallmarks of Cancer. Cell, 2011 Well differentiated liposarcoma Myxoid liposarcoma pathology Schwannoma pathology Previous Next

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< Back Dr. Osman Emre Aycan Aneurysmal Bone Cyst (ABC) Aneurysmal bone cyst (ABC) is a benign but locally aggressive, expansile osteolytic lesion composed of blood-filled cavities separated by fibrous septa. It primarily affects children and young adults, typically in the first two decades of life, with no clear sex predilection. Although non-malignant, it can cause significant pain, swelling, and pathological fractures due to rapid growth and cortical thinning. Epidemiology Accounts for approximately 1–2% of all primary bone tumors . Most common sites: long bones (femur, tibia, humerus) and posterior elements of the spine . Less frequently seen in the pelvis, clavicle, or small bones of the hands and feet. Pathophysiology The exact etiology remains unclear, but two forms are recognized: Primary ABC – arises de novo, often associated with a translocation involving the USP6 gene (17p13) , leading to osteolytic activity and vascular proliferation. Secondary ABC – develops in association with another lesion such as giant cell tumor, chondroblastoma, osteoblastoma, or fibrous dysplasia . The lesion consists of multiple blood-filled spaces without endothelial lining , separated by septa containing fibroblasts, osteoclast-type giant cells, and reactive bone. Clinical Presentation Progressive pain, swelling, and restricted motion near the affected site. Palpable mass may be present. Pathologic fracture is a common first presentation in long bones. Neurological deficits can occur when lesions arise in the spine due to canal compression. Imaging Features Radiographs: Expansile, lytic lesion with “blow-out” or balloon-like appearance . Thin cortical shell and possible septations. May show fluid–fluid levels if internal hemorrhage is present. MRI: Multiple fluid–fluid levels due to different blood degradation stages. Surrounding bone marrow edema and soft tissue extension are possible. Contrast enhancement in septa but not in cystic cavities. CT: Useful for cortical evaluation and surgical planning. Histopathology Multiple cystic spaces filled with blood, lacking endothelial lining . Septa contain fibroblasts, osteoid tissue, and multinucleated giant cells. No malignant cells are present. Differential Diagnosis Lesion Distinguishing Features Telangiectatic Osteosarcoma Malignant cells, atypia, and osteoid production Giant Cell Tumor (GCT) Occurs after skeletal maturity, lacks fluid–fluid levels Chondroblastoma Epiphyseal location, presence of calcifications Fibrous Dysplasia Ground-glass matrix, lacks hemorrhagic cavities Simple Bone Cyst Single cavity, no septations, usually in metaphysis Treatment Management depends on lesion size, location, and aggressiveness: Extended curettage and high-speed burring – mainstay for most cases. Adjuvant therapies to reduce recurrence:Argon beam coagulation, phenol, or liquid nitrogen. Filling of cavity with bone graft or bone cement . Selective arterial embolization (SAE) – used for spinal or pelvic lesions or as preoperative adjunct. Percutaneous sclerotherapy (e.g., doxycycline or polidocanol) is increasingly used as a minimally invasive alternative. En bloc resection reserved for recurrent or inaccessible lesions. Prognosis Recurrence rate: 10–30%, usually within the first two years post-treatment. Risk factors for recurrence include younger age , open physes , and incomplete excision . Long-term prognosis is excellent with appropriate treatment; malignant transformation is exceedingly rare. Key Points ABC is a benign, vascular, expansile bone lesion with locally destructive potential. USP6 translocation confirms diagnosis in ambiguous cases. Fluid–fluid levels on MRI are suggestive but not pathognomonic. Minimally invasive approaches (e.g., sclerotherapy, embolization ) show recurrence rates comparable to surgery in recent studies. Extended curettage with adjuvant remains the gold standard for accessible lesions in long bones. Recurrent cases may benefit from a combined strategy (embolization → curettage → bone graft). References Oliveira AM et al. USP6 Gene Rearrangement in Aneurysmal Bone Cyst. Am J Pathol. 2021;191(7):1210–1220. Mascard E, Gomez-Brouchet A, Lambot K. Aneurysmal Bone Cyst: Clinical and Therapeutic Update. Orthop Traumatol Surg Res. 2015;101(1 Suppl)–S19. Park HY et al. Treatment of Aneurysmal Bone Cysts: A Review of Current Concepts. J Bone Joint Surg Am. 2020;102(4):280–289. Rastogi S et al. Percutaneous Doxycycline Sclerotherapy in Aneurysmal Bone Cyst. J Orthop Surg. 2019;27(3):2309499019878422. Rapp TB et al. Aneurysmal Bone Cyst: A Review of Pathophysiology and Current Management. J Am Acad Orthop Surg. 2012;20(4):233–241. Treatment Modality Description / Technique Recurrence Rate Advantages Limitations / Complications Extended Curettage + Adjuvant (Phenol / Argon / Cryotherapy) Thorough curettage of lesion cavity with mechanical and chemical adjuvant use 10–25% Effective local control, joint preservation Risk of growth plate injury or fracture Curettage + Bone Graft / Bone Cement Filling Cavity filled after curettage to provide stability 15–20% Restores bone strength, simple procedure Possible graft resorption, infection En Bloc Resection Complete excision with margin of healthy bone <10% Lowest recurrence rate Loss of function, reconstructive need Selective Arterial Embolization (SAE) Preoperative or definitive occlusion of feeding vessels 10–20% Minimally invasive, useful in spine/pelvis Risk of incomplete occlusion, recurrence Percutaneous Sclerotherapy (Doxycycline / Polidocanol) Chemical ablation via multiple percutaneous injections 5–15% Outpatient, minimal morbidity, excellent cosmetic results Requires multiple sessions, rare skin necrosis Radiotherapy (rarely used) Reserved for inoperable or recurrent cases Variable (~20%) Non-surgical alternative Radiation-induced sarcoma risk, growth disturbance Treatment Options and Recurrence Rates in Aneurysmal Bone Cyst (ABC) Axial and coronal MRI images of the sacrum demonstrate an expansile, multiloculated cystic lesion centered at the S1 level. The lesion shows multiple fluid–fluid levels with low-to-intermediate signal on T1-weighted, high signal on T2-weighted images, and thin peripheral and septal enhancement after gadolinium administration. Imaging features are characteristic of a benign aneurysmal bone cyst without evidence of solid enhancement or soft-tissue invasion. Previous Next