Case Series: How to Recognize, Treat Aneurysmal Bone Cyst of Clavicle

Aneurysmal bone cyst (ABC) is a benign but locally aggressive bone tumor that rarely develops in the clavicle. Only 62 cases have been reported in medical literature, many of them in broader studies that did not explicitly describe the clavicular cases.

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Massachusetts General Hospital researchers including Courtney L. Kaiser, BA, and orthopaedic oncology surgeon Santiago A. Lozano-Calderon, MD, PhD, recently published the largest known series of ABCs of the clavicle. In the Journal of Shoulder and Elbow Surgery, they report on 13 patients and provide guidance for the diagnosis and treatment of this rare condition.

The researchers reviewed all patients who were treated for an ABC of the clavicle at Mass General between 1976 and 2015. Of the 13 identified patients, seven were male. The average age at diagnosis was 17 years old. All of the ABCs were primary lesions.

As is typical, patients' presenting symptoms offered little diagnostic insight:

• Pain/tenderness (n = 10)
• Swelling (n = 10)
• Decreased range of motion (n = 3)

The radiographic appearance was also typical in all cases: a "blowout" or "soap bubble" in the periosteum. Four patients (31%) sustained a pathologic fracture of the clavicle.

Previous studies have identified the lateral end of the clavicle as the most common location for lesions. In most of the patients, the ABC affected the lateral third of the clavicle (n = 10, 77%), and the researchers speculate that developmental differences of the lateral end make it more prone to tumorigenesis.

In all patients, diagnosis of ABC was made by biopsy specimen. The researchers emphasize that biopsy is essential when an ABC is suspected at any site. ABCs share clinical and radiologic features with other lesions, most ominously telangiectatic osteosarcoma, but also giant cell tumor of bone, chondromyxoid fibroma and unicameral bone cyst. Furthermore, about a third of ABCs are secondary to other bone tumors, such as chondroblastoma, giant cell tumor, nonossifying fibroma or fibrous dysplasia.

In the current series, one of the 13 patients was lost to follow-up after diagnosis. The others were initially treated as follows:

• Curettage alone (n = 5)
• Curettage with allograft packing (n = 4)
• Curettage with autograft packing (n = 2)
• Partial resection with reconstruction (n = 1)

Seven patients (58%) had at least one recurrence, and two patients had more than one recurrence. Two patients were lost to follow-up after initial treatment. The average time to recurrence was six months (range, 1–17 months), which squares with previous case reports.

Dr. Lozano-Calderon and his colleagues explain that the best form of treatment is still being debated. For ABC in general, wide resection is associated with the lowest rate of recurrence. In this series, the patient who initially underwent resection did not have a recurrence, and the two patients who had resection after recurrence did not have a subsequent recurrence.

The clavicle is an expendable bone so wide that resection may be more feasible for aggressive ABCs of the clavicle than in other sites. This is especially true if the coracoclavicular ligaments can be preserved partially or entirely.

The authors also note that ABCs can arise after the first two decades of life. Three of the patients in this series were in their 20s, and one was 46. The latter patient was initially misdiagnosed as having arthritis of the acromioclavicular joint.

Even though ABC is rare, the authors say it should be included in the differential when assessing middle-aged and older patients with shoulder pain.

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