Image Quiz

Elbow-Swelling in a Twelve-Year-Old Boy (continued)

Answer: Aneurysmal bone cyst of the distal metaphyseal region of the left humerus with pathologic fracture.

Fig. 1-A

Fig. 1-B

Figs. 1-A and 1-B Anteroposterior (Fig. 1-A) and lateral (Fig. 1-B) plain radiographs of the left elbow and distal aspect of the left humerus, demonstrating a radiolucent lesion (arrow) involving the distal metaphysis of the humerus. Expansion and thinning of the cortical bone are present.

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Fig. 2-A

Fig. 2-B

Fig. 2-A Axial T1-weighted magnetic resonance image demonstrating the involvement of the distal metaphysis of the left humerus and the multiple fluid-filled levels (arrows).
Fig. 2-B Axial T2-weighted magnetic resonance image shows a multiloculated cystic lesion with septations (thick arrow) and fluid-fluid levels (thin arrows).

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After review of the imaging studies, an open biopsy with intraoperative frozen-section analysis was performed (Figs 3-A and 3-B). Histologic images of the sample are shown.

Fig. 3-A

Fig. 3-B

Fig. 3-A Medium-power photomicrograph of the biopsy specimen, demonstrating a large cyst-like space and the hemorrhage in the surrounding stromal tissue.
Fig. 3-B The area in the center of the photomicrograph shows blood-filled spaces in the stroma of this lesion. The walls of the spaces contain spindle cells and multinucleated cells. The septa contain hemosiderin-laden macrophages.

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This patient was evaluated with use of an open incisional biopsy with intraoperative frozen-section analysis for confirmation of diagnosis. Intralesional curettage was performed through a large cortical window that had been made through the thinnest wall of the cyst. The interior cyst wall was visualized with the aid of loupe and headlamp and was systematically cauterized with use of the electrocautery and then thinned with use of a high-speed burr. A solution of 8% phenol was applied to the cyst wall, after which grafting was performed with use of allogeneic bone graft and 5% phenol.

Discussion

Aneurysmal bone cysts are rare, benign, non-neoplastic and vascular bone lesions that are seen in patients who are between ten and twenty years of age. They can be seen in almost every skeletal site. The most common areas of occurrence are in the long bones and in the posterior elements of the spine. They tend to occur in areas of rapid bone growth. In the long bones, the lesion may be either central (as in this case) or eccentric in the metaphysis. Pain is the presenting symptom in 70% of patients. Pathologic fracture (usually microfracture) is both a common presentation and a complication¹.

The radiographic hallmarks of an aneurysmal bone cyst are a septated, eccentric expansile lesion (blow-out) of bone with a thin surrounding shell of cortical bone². Although plain radiographs usually are sufficient for evaluation of the lesion, magnetic resonance imaging findings are rather characteristic and usually allow a more specific diagnosis. These magnetic resonance imaging findings include a well-defined lesion with a narrow zone of transition, an intact rim of low-intensity signal surrounding the lesion, cystic cavities with fluid-fluid levels, and multiple internal septations. The differential diagnosis may include unicameral bone cyst, chondroblastoma, eosinophilic granuloma, and chondromyxoid fibroma. When diagnosis is still in doubt after plain-film imaging, magnetic resonance imaging is helpful in achieving the diagnosis^3,4.

After a careful history has been acquired and a physical examination has been performed, a radiographic evaluation will give the most detailed information about possible skeletal pathology. Diagnosing musculoskeletal pain in children can present a challenge. Most musculoskeletal disorders in children are benign, but it is important to distinguish benign disorders from those involving malignant tumors and/or infection.

Histologically, aneurysmal bone cysts are not true cysts but rather a sponge-like collection of blood-filled osseous septa lined with fibrous tissue. These septa contain multinucleated giant cells, fibroblasts, dilated capillaries, hemosiderin deposits, and reactive osteoid or bone¹.

Aneurysmal bone cysts are benign but locally aggressive lesions that can appear with variable local behavior. They require surgical intervention. Different surgical modalities have been reported for management of aneurysmal bone cysts. The authors have published their four-step approach for surgical treatment: intralesional curettage through a wide cortical window; cauterization of the cyst wall with use of electrocautery and additional exploration of the cyst wall for subtle crevices or pockets of residual tissue; thinning of the cyst wall with use of a high-speed burr; and administration of adjuvant therapy, such as phenol (5%) or hydrogen peroxide solution, for a recurrent or locally aggressive cyst⁵. Care must be taken to avoid injury to an open physis. Bone-grafting can consist of autograft, allograft, bone substitutes, or a combination of these⁵.

The most important step in the treatment of aneurysmal bone cyst is an accurate diagnosis and understanding of the natural history of the lesion. Intraoperative frozen-section analysis with histological confirmation of the diagnosis is the initial part of the procedure. The diagnosis will guide the physician not only in choosing the treatment but also in making the prognosis. Magnetic resonance imaging is occasionally helpful, and a histological examination for confirmation is essential.

Reports of overall postsurgical recurrence rates vary widely, ranging from 10% to 59% after various surgical removal techniques^5,6. Results with regard to age-based recurrence in children have been also reported⁵. In 1970, Biesecker et al. reported a trend for a higher recurrence rate in children who were younger than fifteen years in comparison with the rate seen in older patients⁷. Freiberg at al. reported recurrences after surgical treatment of aneurysmal bone cyst in five of seven children who were ten years or younger⁴. In 1999, Gibbs et al. reported a higher recurrence rate of aneurysmal bone cyst in children who were ten years of age or younger compared with patients who ranged in age from eleven to fifty-eight years⁶. {In 2004, the senior author (J.P.D.) reported persistence or recurrence of primary aneurysmal bone cyst in three of thirteen children who were ten years of age or younger and in five of thirty-two children who were older than ten years⁵. The recurrence rate for aneurysmal bone cyst in children who were younger than ten years was lower in that study than in previous studies, and the cure rate was 82% after the initial surgery with use of the above-mentioned technique⁵.

*The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

References

1. Dormans JP, Pill SG. Fractures through bone cysts: unicameral bone cysts, aneurysmal bone cysts, fibrous cortical defects, and nonossifying fibromas. Instr Course Lect. 2002;51:457-67.
2. Woertler K, Brinkschmidt C. Imaging features of subperiosteal aneurysmal bone cyst. Acta Radiol. 2002;43;336-9.
3. Sullivan RJ, Meyer JS, Dormans JP, Davidson RS. Diagnosing aneurysmal and unicameral bone cysts with magnetic resonance imaging. Clin Orthop Relat Res. 1999;366:186-90.
4. Freiberg AA, Loder RT, Heidelberger KP, Hensinger RN. Aneurysmal bone cyst in young children. J Pediatr Orthop. 1994;14:86-9.
5. Dormans JP, Hanna BG, Johnston DR, Khurana JS. Surgical treatment and recurrence rate of aneurysmal bone cysts in children. Clin Orthop Relat Res. 2004;421:205-11.
6. Gibbs CP Jr, Hefele MC, Peabody TD, Montaq AG, Aithal V, Simon MA. Aneurysmal bone cyst of the extremities. Factors related to local recurrence after curettage with a high-speed burr. J Bone Joint Surg Am. 1999;81:1671-8.
7. Biesecker JL, Marcove RC, Huvos AG, Mike V. Aneurysmal bone cysts. A clinicopathologic study of 66 cases. Cancer. 1970;26:615-25.