Aneurysmal bone cyst, multiple sites

This code represents an aneurysmal bone cyst (ABC) affecting multiple anatomical locations. An ABC is a benign, expansile, osteolytic bone lesion characterized by blood-filled spaces separated by fibrous septa and osteoclast-like giant cells. While typically solitary, this specific code indicates the presence of these cysts in more than one bone or site.

Use this code when documentation clearly indicates the diagnosis of an aneurysmal bone cyst impacting multiple distinct skeletal sites. This applies to cases where imaging (e.g., X-ray, MRI) and/or biopsy confirm the presence of ABCs in various bones. Documentation should specify the "multiple sites" to support this code.

• Ensure documentation explicitly states "multiple sites" or lists several distinct anatomical locations affected by the aneurysmal bone cyst.
• Do not use this code for a solitary aneurysmal bone cyst, even if it is large or complex; site-specific codes (M85.50-M85.58) would be more appropriate.
• Consider sequencing this code as a primary diagnosis if it is the reason for the encounter, or as a secondary diagnosis if it is a co-morbidity being managed.