Clinical Example: Aneurysmal Bone Cysts

Aneurysmal bone cysts are uncommon benign vascular bone tumors. Their origin is unknown, but they resemble intraosseous arteriovenous malformations. They may cause cortical expansion and thinning, leading to pathologic fracture. They are more common in females than males, in young patients (less than 20 years old) and in the lower extremities, pelvis and spine. The most common treatment is curettage. One out of five will recur after curettage. After excision, treatment of the margins with cryotherapy, phenol or methacrylate may reduce recurrence. However, if there is structural weakening from circumferential cortical thinning, cytotoxic marginal treatment may may be too risky and structural bone grafting may be required.

The following two cases are each an atypical demographic: elderly, male, upper extremity. 
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Case 1
This 75 year old gentleman complained of three months of wrist pain severe enough to prevent playing golf. Plain films showed a well circumscribed lobular lucency in the capitate and STT osteoarthritis.
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MRI was interpreted as inconclusive, differential including an intraosseous cyst or giant cell tumor with cortical thinning but no suggestion of malignancy.
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Dorsal exposure of the capitate revealed extraosseous extension.
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The dorsal capitate was windowed and the tumor was removed with rongeur and curette. Margins were taken back to subcortical bone with a high speed burr.

Technical point:
The irregular texture of cancellous bone makes it difficult to visually inspect the margins, and the use of a small curette only makes this worse. Once the gross tumor is removed, the margins can be "polished" with a large high speed burr - the larger the better. This leaves a a smooth surface and reduces the chance of residual hidden pockets of tumor.
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Intraoperative fluoroscopy of the defect after marginal excision with a burr...
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and then after the defect was filled with corticocancellous iliac crest bone graft to improve structural stability:
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Pressure fit bone graft in place.
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Pathology: decalcified specimen showed empty spaces, hemorrhage, stromal elements and multinuclear osteoclasts - not to be confused with giant cells.
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Graft incorporation at 6 months postop.
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Case 2
This elderly gentleman presented with an enlaging tumor of his thumb tip.  He did not know how long it had been present. He complained that it bled frequently, was unstable, and he requested an amputation. He had no lymphadenopathy or evidence of metastatic disease on chest Xray.
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Plain films showed loss of the distal 2/3 of the distal phalanx.
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Excisional biopsy in the form of an interphalangeal disarticulation:
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Gross pathology after decalcification.
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Microscopic pathology similar to the prior case, confirming the diagnosis of aneurysmal bone cyst.
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