Tumor-Like Lesions of Bone

Tumor-Like Lesions of Bone

Tumor-Like Lesions of Bone

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Intro & Fibrous Lesions - Bone's Benign Bafflers

  • Tumor-Like Lesions:
    • Non-neoplastic, reactive/developmental bone changes.
    • Key differences from true tumors: No malignant potential, often self-limiting, distinct histology (not frankly neoplastic).
  • Fibrous Dysplasia (FD):
    • Benign fibro-osseous lesion; GNAS1 gene mutation.
    • Types:
      • Monostotic (single bone), Polyostotic (multiple bones).
      • McCune-Albright Syndrome: 📌 3 P's: Polyostotic FD, Pigmentation (café-au-lait, "coast of Maine"), Precocious puberty/endocrinopathy.
    • X-ray: "Ground glass" opacity, "Shepherd's crook" deformity (femur). Fibrous dysplasia with shepherd's crook deformity
  • Non-ossifying Fibroma (NOF) / Fibrous Cortical Defect (FCD):
    • Common developmental defect; FCD < 3 cm, NOF > 3 cm.
    • Children/adolescents (long bone metaphysis).
    • Often asymptomatic, incidental; most resolve spontaneously.
    • X-ray: Eccentric, lytic, well-defined sclerotic rim, "soap bubble" look.

⭐ McCune-Albright syndrome: polyostotic fibrous dysplasia, café-au-lait spots (coast of Maine), endocrinopathies (e.g., precocious puberty).

Cystic & Histiocytic Lesions - Cavities & Characters

  • Simple Bone Cyst (SBC) / Unicameral Bone Cyst (UBC)

    • Location: Central, metaphyseal (proximal humerus/femur common).
    • Content: Fluid-filled cavity.
    • X-ray: 'Fallen leaf' sign (pathognomonic if cortical fragment seen in dependent part of cyst).

      ⭐ The 'fallen leaf' sign, a fragment of cortical bone that has fractured and settled into the dependent portion of a fluid-filled simple bone cyst, is highly suggestive of this lesion.

  • Aneurysmal Bone Cyst (ABC)

    • Location: Eccentric, expansile, lytic lesion.
    • Content: Blood-filled cavities; not a true cyst (no epithelial lining).
    • Imaging: 'Fluid-fluid levels' on MRI/CT.
    • Types: Can be primary or secondary (to GCT, chondroblastoma, etc.).
    • 📌 Mnemonic: A Bloody Cyst.
  • Eosinophilic Granuloma (EG) (Langerhans Cell Histiocytosis - LCH)

    • Age: Children & young adults.
    • X-ray: Lytic lesions.
      • Skull: 'Punched-out' lesions.
      • Spine: 'Vertebra plana' (coin-on-edge appearance).
    • Microscopy: Birbeck granules (tennis-racket shaped) on Electron Microscopy (EM) in Langerhans cells.

Metabolic, Reparative & Dx - Reactive Responders

  • Brown Tumor (Osteitis Fibrosa Cystica):
    • Pathophysiology: Hyperparathyroidism (1°/2°) causes ↑ osteoclastic bone resorption.
    • Radiology: Well-defined, lytic, expansile lesions. "Brown" from hemosiderin.
    • Common Sites: Mandible, clavicle, ribs, pelvis, long bones.

    ⭐ Not a true neoplasm. Regresses with hyperparathyroidism correction.

  • Giant Cell Reparative Granuloma (GCRG):
    • Location: Jaw bones (mandible > maxilla); small bones of hands/feet.
    • Radiology: Lytic, uni/multilocular, variable margins.
    • Histology: Fibrous stroma, giant cells (fewer vs GCT), hemorrhage, hemosiderin. Distinct from GCT. X-ray of lytic lesions in pelvis and femur
  • Diagnostic Approach (Tumor-Like Lesions):
    • Evaluation: Age, location (epiphysis, metaphysis, diaphysis). X-ray features (lytic/sclerotic, margins, matrix, periosteal reaction).
    • Further Steps:
-   Biopsy: Crucial if diagnosis uncertain or malignancy suspected after imaging.
  • General Management Principles:
    • Asymptomatic & Stable: Observation, serial imaging.
    • Symptomatic/Progressive: Curettage common. Bone graft/substitutes (PMMA) for defects.
    • Underlying Cause: Treat (e.g., parathyroidectomy for Brown Tumor; Vit D for rickets).

High‑Yield Points - ⚡ Biggest Takeaways

  • Tumor-like lesions are non-neoplastic, mimicking true bone tumors.
  • Fibrous dysplasia: Ground-glass matrix, Shepherd's crook deformity, McCune-Albright syndrome.
  • Non-ossifying fibroma (NOF): Common, eccentric lytic lesion, asymptomatic, may regress spontaneously.
  • Simple Bone Cyst (SBC): Central lytic, proximal humerus/femur, "fallen leaf" sign.
  • Aneurysmal Bone Cyst (ABC): Expansile, blood-filled, "fluid-fluid levels" on MRI.
  • Eosinophilic granuloma (LCH): Lytic lesions, vertebra plana in children, skull involvement.
  • Brown Tumor: Due to hyperparathyroidism and increased osteoclastic activity.

Practice Questions: Tumor-Like Lesions of Bone

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Radiographically, the lesion shown in the image could be:

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Flashcards: Tumor-Like Lesions of Bone

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Osteoma is a benign tumor of _____ that is seen in middle age

Hint: what overall type of structure?

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Osteoma is a benign tumor of _____ that is seen in middle age

bone

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