distinguish UBC from aneurysmal bone cyst (ABC) Orthopedic Oncology cases 1

A 10-year-old male presents to the emergency room complaining of right shoulder pain after falling during a soccer game. He denies history of pain in the shoulder or arm prior to the injury. X-rays taken in the emergency room are shown in Figure 8–1A and B.

 

 

 

Figure 8–1 A–B

 

Which of the following is true of the lesion shown in the x-ray image?

1. Most common location is mid-diaphyseal in long bones

2. It is commonly filled with blood

3. It is usually associated with a soft-tissue mass

4. The natural history of this lesion is to fill in with bone as patient reaches skeletal maturity

Discussion

The correct answer is (D). The lesion shown in the x-rays is a unicameral bone cyst (UBC), which is a common, serous fluid-filled bone lesion that usually occurs in patients younger than 20 years of age. The natural history is that these lesions fill in with bone over time and may be asymptomatic unless the patient develops pathologic fracture. Unlike aneurysmal bone cysts, which are often filled with blood, a UBC rarely includes blood unless fracture is present. Cortical thinning may be seen on x-ray, but bone remodeling does not exceed the width of the physis and these lesions do not have associated soft-tissue masses.

What is the most appropriate emergency room management of this patient?

1. Admission to the hospital for immediate surgical treatment

2. Sling and nonweight bearing on the extremity now, with potential surgical management once fracture is healed

3. CT and MRI to evaluate extent of soft-tissue mass

4. Bone biopsy to document osteomyelitis and obtain culture, and IV antibiotics

 

Discussion

The correct answer is (B). Unicameral bone cysts with pathologic fracture do not routinely require cross-sectional imaging, as their radiographic characteristics allow them to be easily diagnosed on plain radiograph. A minimally displaced fracture such as this generally does not require surgical stabilization in the acute period. This fracture should be allowed to heal prior to treatment of the lesion. The x-ray shows characteristics more consistent with UBC than osteomyelitis.

In the absence of pathologic fracture, what is the first line of surgical treatment?

1. Curettage with bone grafting

2. Internal fixation

3. Aspiration and injection with methyl prednisolone acetate

4. Wide resection and reconstruction with humeral endoprosthetic implant

 

Discussion

The correct answer is (C). The initial surgical treatment of UBC is with aspiration and injection with methylprednisolone acetate. Internal fixation is generally not indicated except in high stress areas likely to undergo pathologic fracture. Curettage and bone grafting can be used in cases in which aspiration and injection fails. Wide resection and reconstruction is reserved for malignant tumors.

If found in the proximal femur, management of this lesion with or without pathologic fracture would consist of:

1. Wide resection and proximal femur reconstruction

2. Wide resection, reconstruction, and postoperative radiation

3. Curettage, bone grafting, and internal fixation

4. Percutaneous screw fixation alone

 

Discussion

The correct answer is (C). When a UBC is found in the proximal femur, curettage, bone grafting, and internal fixation are recommended to prevent pathologic fracture. In other locations where the risk of pathologic fracture is lower, standard treatment is generally intralesional injection of methylprednisolone acetate. Wide resection and radiation therapy are not necessary, as UBC is a benign lesion.

 

Objectives: Did you learn...?

 

Characteristic features of simple, or unicameral, bone cysts, and features that distinguish UBC from aneurysmal bone cyst (ABC)?

 

 

Acute and overall management of simple bone cysts? Indications of surgery for simple bone cysts?