Working Diagnosis:
Pathological hip fracture due to aneurysmal bone cyst

Treatment:
Under regional spinal anesthesia, the patient underwent a bipolar arthroplasty of the right hip and an open biopsy of the right femoral head.

Pathology sections showed a perforation of small stromal cells associated with scattered giant cells that have features highly suggestive of an aneurysmal bone cyst. Case Photo #2

Outcome:
On post surgical date two, the patient's oxygen saturation reduced to 84% and he became tachycardic in the 120s. Despite the use of heparin for deep venous thrombosis prophylaxis, there was concern for a pulmonary embolism. A computer tomography angiogram of the chest was inconclusive, and a ventilation-perfusion (VQ) scan illustrated low probability of a pulmonary embolism. Treatment dose Lovenox was started since the Well's Score of six suggested moderate probability. Upon clinical improvement, the patient underwent inpatient physical therapy for balance, gait, and stair mobility training. The patient was discharged with Rivaroxiban, and he was given instructions to avoid flexion and adduction for the first three months after surgery with no limitations thereafter. Outpatient follow-up included interval evaluation with his orthopedic surgeon for 1 to 2 years and outpatient physical therapy to continue gait training and general lower extremity strength exercises.

Author's Comments:
The World Health Organization describes an aneurysmal bone cyst as "an expanding osteolytic lesion consisting of blood-filled spaces of variable size separated by trabeculae or osteoid tissue and osteoclast giant cells." This benign tumor predominantly affects patients in the second decade of life and is most commonly found in the metaphysis of long tubular bones, followed by the spine and flat bones. Aneurysmal bone cysts are rare, constituting 1 to 6% of all primary bone tumors. In fact, incidence estimates are 0.14 per 100,000 people, although this may falsely be low due to spontaneous regression and clinically silent cases. The etiology has not been conclusively identified, but there is an association with a chromosomal aberration translocation 16 and 17. Currently, intralesional curettage with bone grafting is the first line of treatment. Other treatment options include: cryotherapy, sclerotherapy, radionuclide ablation, arterial embolization, and en bloc resection. Recurrence rates of treated aneurysmal bone cysts are minimal, and the risks and benefits of each procedure must be tailored to the goals of each patient.

Editor's Comments:
Benign pediatric-adolescent bone tumors are classified according to the matrix or substance that they form. The 4 main classifications include cartilage, cystic/vascular, fibrous and osteoid. They are further categorized according to their proclivity for expansion: static versus aggressive.

First described by Jaffe and Lichtenstein in 1942, aneurysmal bone cysts (ABCs) are considered locally aggressive or expansile vascular lesions that have a slight predilection for females. They tend to be solitary and grow until treated, and they may be either a primary or secondary etiology. The latter accounts for approximately 30% of occurrences and may be associated with a chondroblastoma, chondromyxoid fibroma, fibrous dysplasia, giant cell tumor, or osteoblastoma. (5,10) Although aneurysmal bone cysts may develop in any bone, they are most commonly found in the distal femur, lumbar posterior spinal elements, and proximal tibia. Thus, aneurysmal bone cysts are not only rare as detailed above but uncommonly present as hip pain when they do occur.

When considering this case, it is important to note the insidious onset followed by an acute atraumatic injury. Prior to his pathologic fracture, the aneurysmal cyst may have been identified on standard radiographs of the hip and pelvis as a well-circumscribed osteolytic lesion with thin sclerotic rim, "soap bubble" appearance and possible periosteal reaction. Advanced imaging with magnetic resonance imaging and computed tomography may help to further define the pathology and its presentation.

Historically, the rates of recurrence following intralesional curettage alone were quite high, up to 60%. (8) Advancements in surgical technique, including cauterization, dilute phenolization, and extended curettage with a high-speed burr of the cyst wall, have drastically reduced this rate to about 10%. (3) Recurrence typically occurs within 6 months, but it may have a delayed presentation. En-bloc resection provides the lowest recurrence rate with potential to be curative. Novel treatment with denosumab, a human monoclonal antibody, has been reported and may be considered when treating areas not easily accessible or amenable to surgery.

Despite the patient's young age, relative good health, and use of prophylactic heparin therapy, he experienced an acute desaturation in the post-operative period. Th which may have been secondary to a thrombosis versus fat embolism. Although the work-up was inconclusive for a pulmonary embolism which may have been related to either a migrated deep vein thrombosis or fat embolism, this event highlights the importance of a thorough well-informed consent that addresses even the unlikely but potentially serious complication.

References:
1. Biermann JS, Ed. Stanitski CL. Common Benign Lesions of Bone in Children and Adolescents. Journal of Pediatric Orthopedics. 2002;22:268-273.

2. Copley L, Dormans JP. Benign Pediatric Bone Tumors. Common Orthopedic Problems. 1996;43(4):949-965.

3. Gibbs CP Jr, Hefele MC, Peabody TD, Montag 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;81:1671-1678.

4. Jaffe HL. Solitary unicameral bone cyst: With emphasis on the roentgen picture. the pathologic appearance, and the pathogenesis. Arch Surg. 1942;44:1004-1025.

5. Mascard E, Gomez-Brouchet A, Lambot K. Bone cysts: unicameral and aneurysmal bone cyst. Orthop Traumatol Surg Res. 2015;101:S119-S127.

6. Parashari UC, Khanduri S, Upadhyay D, Bhadury S, Singhal S. Radiologic and pathologic correlation of aneurysmal bone cysts at unusual sites. J Can Res Ther. 2012;8:103-105.

7. Rapp TB, Ward JP, Alaia MJ. Aneurysmal Bone Cyst. Journal of the American Academy of Orthopedic Surgeons. 2012;20(4):233-241.

8. Ravindra VM, Eli IM, Schmidt MH, Brockmeyer DL. Review of Pathology and Surgical Decision Making. Neurosurg Focus. 2016;41(2):1-14.

9. Schreuder HW, Veth RP, Pruszczynski M, Lemmens JA, Koops HS, Molenaar WM. Aneurysmal bone cysts treated by curettage, cryotherapy and bone grafting. J Bone Joint Surg BR. 1997;79:20-25.

10. Sharma M, Velho V, Kharosekar H. Primary aneurysmal bone cyst of the petrous temporal bone: A case report and review of the literature. Asian J Neurosurg. 2016;11(4):444-450.

Return To The Case Studies List.