Clinical presentation:
Female aged 49 years, sudden onset of pain in the left elbow, after a fall.

There is a pathological fracture of the olecranon of the left ulna, through a lytic lesion in the bone. The cyst-like lesion lies immediately adjacent to the elbow joint and has a well-defined margin. The endosteal margin has a narrow zone of transition between normal and abnormal bone. There is no indication of a lamellar periosteal reaction. The skeleton is mature. Anterior soft tissue density is probably an elbow joint effusion.