Solitary bone cyst, unspecified site

This code identifies a benign, fluid-filled lesion within a bone that is not further specified by anatomical location. These cysts are typically asymptomatic and often discovered incidentally on imaging studies. They represent a localized area of bone destruction and replacement by fibrous tissue and fluid.

Assign this code when documentation confirms a diagnosis of a solitary bone cyst without specifying the affected bone. This is appropriate when the physician's notes indicate "solitary bone cyst" or "unicameral bone cyst" but do not provide a more precise anatomical site. Ensure the documentation clearly states the cyst is solitary, as opposed to multiple.

• Avoid using this code if a more specific anatomical site (e.g., humerus, femur) is documented; instead, use the appropriate M85.4- subcategory.
• Do not confuse with aneurysmal bone cysts (M85.5-), which are distinct entities with different pathological characteristics.
• This code should be used when the site is truly unspecified, not merely unknown at the time of initial coding.