IS Case 352: Simple, solitary or unicameral bone cyst
2009 URMC Imaging Sciences
Publication Date: 2009-11-09
There is a circumscribed, lucent lesion following the long axis of the humerus with sclerotic margins and central location in the metaphysis adjacent to the physis. There is a fracture through the lesion with a "fallen fragment of bone within the lucent lesion. As the patient grew, the lesion became sclerotic and migrated into the diaphysis.
Simple bone cysts are of unknown etiology, but may occur secondary to disrupted growth of bone via trauma or vascular abnormality. They are typically seen in patients younger than 20 years old with a male predominance. Most occur in the proximal diaphysis of the humerus or femur. They can be seen in the calcaneus, talus and ileum in more mature patients.
Plain radiography is usually diagnostic. MRI demonstrates cyst characteristics with low to intermediate T1 signal intensity and hyperintense T2 signal. CT and MRI are reserved for atypical cases. Surgical curettage demonstrates a paucity of solid tissue.
Simple bone cysts can become fractured in two-thirds of cases and are usually asymptomatic unless fracture occurs. The "fallen fragment" sign occurs when a fragment of cortex is seen inside the empty or fluid-filled lesion, but occurs in few cases. This sign differentiates simple bone cyst from other similar appearing fibrous or cartilaginous lesions.
Simple bone cysts can heal after fracture and spontaneously regress. When treated, curettage with grafting of bone fragments is usually utilized. With this surgery, there is risk of recurrence and the growth plate injury. Other treatments include cryotherapy, intramedullary nailing, methylprednisolone injection, injection of bone marrow or combinations of any of the previously mentioned methods.
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