Brown tan bony and fibrous tissue 75x45x5mm.
The sections show blood-filled cyst like spaces which are arranged haphazardly within a moderately cellular stroma. Stromal cells have both spindle and epithelioid morphology and show mild nuclear pleomorphism. These are admixed with a large number of osteoclast-like multinucleated cells. Scattered mitotic figures are noted. No necrosis is seen. Irregularly shaped fragments of woven bone are present within the lesion and there is re-modelling of trabeculae of lamellar bone at the periphery of the lesion. No malignant osteoid is identified. The features are of aneurysmal bone cyst.
DIAGNOSIS: Aneurysmal bone cyst.