Aneurysmal bone cyst, unspecified lower leg

This code signifies a benign, fluid-filled lesion within the bone of an unspecified lower leg, characterized by blood-filled spaces separated by fibrous septa. It represents a non-neoplastic bone tumor that can cause pain, swelling, and pathological fractures.

Use this code when documentation confirms an aneurysmal bone cyst located in the lower leg, and the specific laterality (right or left) is not documented. This diagnosis is typically supported by imaging studies such as X-rays, MRI, or CT scans, often followed by biopsy for definitive confirmation.

• Ensure the documentation explicitly states "aneurysmal bone cyst" and specifies the lower leg as the anatomical site.
• If laterality (right or left lower leg) is documented, use the more specific codes M85.561 or M85.562.
• Do not confuse with simple bone cysts (M85.6x) or other benign bone tumors.