IS Case 352: Simple, solitary or unicameral bone cyst

Sara Ann Majewski, MD

Imaging Sciences URMC


2009 URMC Imaging Sciences
Publication Date: 2009-11-09

History

Patient is an 11-year-old male initially presenting status post trauma to the left upper extremity with clinical suspicion for fracture.

Findings

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.

Diagnosis

Simple, solitary or unicameral bone cyst

Discussion

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.

Differential diagnosis also includes aneurysmal bone cysts which have periosteal reaction. Bone abscess is differentiated by periosteal reaction and extension beyond the physis.

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.

Positive response to treatment is seen as decreased cavity size, increased sclerosis, cortical thickening and osseous remodeling on plain radiography.

References

  1. Dahnert WF. Radiology Review Manual. 6th ed., Lippincott Williams & Wilkins: New York, 2007.
  2. Greenspan A. Orthopedic Imaging: A Practical Approach. 4th ed., Lippincott Williams & Wilkins: New York, 2004.
  3. Teo E, Peh WCG. Simple bone cyst. e-Medicine. April 20, 2007. http://emedicine.medscape.com/article/395783-overview

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