Orthopaedic Oncology cases Aneurysmal Bone Cyst.2

A 20-year-old female presents to the office complaining of pain and swelling in the elbow. She denies any recent trauma and reports these symptoms have been progressing over the past year. She denies fever, chills, or recent weight changes. Xray is shown in Figure 8–2.

 

 

 

Figure 8–2

 

Which of the following x-ray findings is most consistent with this lesion?

1. Eccentric, radiolucent lesion that has expanded greater than the width of the epiphysis

2. Central lesion with loss of thin periosteal rim around the lesion

3. Most often accompanied by pathologic fracture

4. Most common location is in small bones of hands and feet, although distal femur is also common

Discussion

The correct answer is (A). Aneurysmal bone cysts are destructive, reactive bone lesions filled with multiple blood-filled cavities. They are eccentric on x-rays and cause bone remodeling which has the appearance of an expanded bone and can be beyond the width of the physis, unlike UBC. They occur most often in the distal femur, proximal tibia, pelvis, and posterior elements of the spine. Unlike giant cell tumors of bone, ABCs usually retain a thin periosteal rim. Unlike UBCs, these lesions cause pain and swelling, and pathologic fracture as a presenting symptom is relatively rare.

The following figure (Fig. 8–3A and B) show a low and high power histologic slide of the lesion. Which of the following best describes the histologic appearance of this lesion?

1. Woven bone, Aneurysmal blood vessels, osteoid producing cells

2. Sheets of small round blue cells with pleiomorphoism and nuclear atypia

3. Cavernous, blood-filled spaces without a true endothelial lining. Multinucleated giant cells within a fibrohistiocytic stroma are noted, without cellular atypia

4. Dense fibrous stroma with storiform pattern and limited nuclear atypia

 

 

 

Figure 8–3 A–B

 

Discussion

The correct answer is (C). The histologic appearance seen in Figure 8–3A and B is best described as a cavernous, blood-filled spaces without a true endothelial lining. Multinucleated giant cells within a fibrohistiocytic stroma are noted, without cellular atypia are seen. This is a classic description of Aneurysmal Bone Cyst.

The patient brings an MRI of the elbow to the office that was ordered by her primary care physician a week prior. What findings would you expect to see that would confirm your diagnosis of ABC?

1. Large soft-tissue mass extending out of the proximal radius bone

2. Skip lesions throughout the radius

3. Fluid–fluid levels

4. Extensive edema within surrounding bone and soft tissue

Discussion

The correct answer is (C). Fluid–fluid levels are commonly seen on T2-weighted MRI, as this finding represents the separation of serum and blood products within the cyst. Skip lesions are metastases of a malignant process. ABCs can remodel the cortex and into surrounding soft tissue but retain their reactive periosteal rim and will not cause a large soft-tissue mass. Edema in the surrounding tissues is not a common finding on MRI in the absence of pathologic fracture.

When imaging is encountered that suggests ABC, which malignancy must also be considered in the differential?

1. Ewing sarcoma

2. Telangiectatic osteosarcoma

3. Periosteal osteosarcoma

4. Giant cell tumor

 

Discussion

The correct answer is (B). While rare, telangiectatic osteosarcoma can mimic ABC radiographically. Histologically, a malignant tumor is seen. Cartilage tumors (enchondroma, chondrosarcoma) will show radiographic characteristics of cartilage: arc-and-ring calcification or an expansile mass on imaging and/or cartilaginous matrix on histology. Periosteal osteosarcoma has a characteristic juxtacortical cloud-like density, and will not show blood-filled spaces on histology. Ewing sarcoma is characterized by periosteal elevation in an “onion-skinning” pattern and on histology is characterized by sheets of small, round blue cells.

 

Objectives: Did you learn...?

 

 

Imaging characteristics of ABC? Histologic features of ABC?

 

 

Important differential diagnosis of telangiectatic osteosarcoma and its features? Treatment of ABC?