Differential diagnosis of expansile diaphyseal lesion of a long bone includes:

Benign Lesions:

• Aneurysmal Bone Cyst (ABC): Expansile, often with fluid-fluid levels.
• Simple Bone Cyst: Central, well-defined lucent lesion.
• Giant Cell Tumor: Usually extends to epiphysis, expansile.
• Fibrous Dysplasia: Ground-glass matrix, fusiform expansion.
• Non-ossifying Fibroma: Eccentric, well-defined, metaphyseal.

Malignant Lesions:

• Telangiectatic Osteosarcoma: Lytic, expansile, mimics ABC.
• Osteosarcoma: Mixed lytic-sclerotic with aggressive periosteal reaction.
• Ewing Sarcoma: Permeative, often diaphyseal, soft tissue mass.
• Metastasis: Rare in diaphysis, expansile in renal, thyroid origin.

Others:

• Plasmacytoma/Multiple Myeloma: Expansile lytic lesion.
• Lymphoma: Variable appearance, may present expansile.
• Infection (e.g., Brodie’s abscess): Can appear expansile with surrounding sclerosis.

Key features like location, patient age, lesion margins, matrix mineralization, periosteal reaction, presence of soft tissue mass, and systemic signs help narrow the diagnosis.

This differential list aids in approaching an expansile diaphyseal lesion of long bones on imaging.Differential diagnosis of expansile diaphyseal lesion of a long bone includes:

• Benign lesions:
  • Aneurysmal bone cyst (ABC)
  • Simple bone cyst
  • Fibrous dysplasia
  • Non-ossifying fibroma
  • Giant cell tumor (may extend into diaphysis)
• Malignant lesions:
  • Telangiectatic osteosarcoma
  • Ewing sarcoma
  • Osteosarcoma (may be expansile)
  • Metastasis (renal cell carcinoma, thyroid, hepatocellular carcinoma)
  • Plasmacytoma